tag:theconversation.com,2011:/us/topics/carbon-cycle-1465/articlesCarbon cycle – The Conversation2024-03-20T19:03:42Ztag:theconversation.com,2011:article/2243352024-03-20T19:03:42Z2024-03-20T19:03:42ZTasmania’s tall eucalypt forests will be wiped out by heatwaves unless we step in to help them<figure><img src="https://images.theconversation.com/files/582418/original/file-20240318-26-dug8wt.jpg?ixlib=rb-1.1.0&rect=22%2C0%2C4898%2C3253&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Nicolas Rakotopare</span></span></figcaption></figure><p>Tasmania’s tall eucalypt forests are globally significant. They <a href="https://www.sciencedirect.com/science/article/abs/pii/S037811270900872X">accumulate carbon faster</a> than any other natural forest ecosystem in the world. </p>
<p>But climate change is making it harder for these forests to remove carbon from the atmosphere and store it in wood. During heatwaves, they <a href="https://www.nature.com/articles/s41598-022-06674-x">stop removing carbon</a> altogether and release it instead.</p>
<p>What will happen as <a href="https://climatefutures.org.au/extreme-events-technical-report/">heatwaves occur more frequently</a>? Tasmania’s tall eucalypt forests will become carbon sources more and more of the time. As temperatures continue to rise, the forests will reach a “<a href="https://www.science.org/doi/full/10.1126/sciadv.aay1052">tipping point</a>”. When this happens the forests will no longer be able to store carbon and mass tree deaths will occur. </p>
<p>My <a href="https://bit.ly/Giants-Under-Threat_Report-2024">new report</a> released today makes recommendations about preparing for this. There are serious implications for greenhouse gas emissions, conservation and wood production. We cannot ignore the risks of a warming climate. There is a lot we can do now to prepare and make future forests more resilient. </p>
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Read more:
<a href="https://theconversation.com/in-heatwave-conditions-tasmanias-tall-eucalypt-forests-no-longer-absorb-carbon-176979">In heatwave conditions, Tasmania’s tall eucalypt forests no longer absorb carbon</a>
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<h2>Forests of immense value</h2>
<p>The <a href="https://whc.unesco.org/en/list/181/">Tasmania Wilderness World Heritage Area</a> is <a href="https://whc.unesco.org/en/news/2344">ranked number one</a> of all UNESCO sites globally for taking carbon out of the atmosphere and storing it. That’s because western Tasmania’s <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/geb.12171">high rainfall and cool temperatures are ideal for forest growth</a>.</p>
<p>These tall eucalypt forests contribute greatly to Tasmania’s claim to net-zero emissions in its <a href="https://recfit.tas.gov.au/__data/assets/pdf_file/0006/440592/Tasmanian_Greenhouse_Gas_Emissions_Report_2023.pdf">greenhouse gas accounts</a>.</p>
<p>The forests have produced most of the high-quality sawlogs supplying Tasmania’s sawmilling industry for more than a century.</p>
<p>They also provide unique and long-lasting habitat for wildlife. Large logs support diverse communities of insects and fungi.</p>
<p>The forest supports unique <a href="https://tahuneadventures.com.au/">tourism experiences</a> and an emerging opportunity for “<a href="https://www.bigtreestate.com/">big tree tourism</a>”.</p>
<p>Tall eucalypt forests are dominated by one or two or three species of <em>Eucalyptus</em>: </p>
<ul>
<li><em>E. obliqua</em> (messmate or stringy bark)</li>
<li><em>E. regnans</em> (swamp gum or mountain ash) </li>
<li><em>E. delegatensis</em> (alpine ash or gum-top stringybark). </li>
</ul>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/582466/original/file-20240318-24-2fq2cg.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/582466/original/file-20240318-24-2fq2cg.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/582466/original/file-20240318-24-2fq2cg.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=831&fit=crop&dpr=1 600w, https://images.theconversation.com/files/582466/original/file-20240318-24-2fq2cg.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=831&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/582466/original/file-20240318-24-2fq2cg.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=831&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/582466/original/file-20240318-24-2fq2cg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1044&fit=crop&dpr=1 754w, https://images.theconversation.com/files/582466/original/file-20240318-24-2fq2cg.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1044&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/582466/original/file-20240318-24-2fq2cg.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1044&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Stringybark flowers <em>(Eucalyptus obliqua)</em></span>
<span class="attribution"><span class="source">Tim Wardlaw</span></span>
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</figure>
<h2>Preparing for tipping points</h2>
<p>As temperatures continue to rise, many ecosystems are predicted to reach a <a href="https://www.science.org/doi/full/10.1126/sciadv.aay1052">tipping point</a>. This is the point at which the ecosystem can no longer function and is eventually replaced by a different ecosystem.</p>
<p>Many plant-based ecosystems, mostly in the tropics, are expected to reach a tipping point within three decades. Tasmania’s tall eucalypt forests may be among them because they share <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0084378">similarities with tropical rainforest</a>. </p>
<p>World Heritage values would be jeopardised, huge amounts of stored carbon would be released, and biodiversity dependent on the tall trees would be threatened. So there is an urgent need to begin preparing now for a future tipping point in these forests. </p>
<p>The main ambition of the measures outlined in my <a href="https://bit.ly/Giants-Under-Threat_Report-2024">report released today</a> is to restore forested areas after the original forest is lost – or damaged irreversibly. The new forests would be grown from the same species of eucalypts but the seed sown would regenerate forests better suited to the new climate than the original forest.</p>
<p>To achieve this ambition, we need to decide what features of tall eucalypt forests we want to retain in future forests. Capacity for rapid growth after disturbance would be high on the list of those features. </p>
<p>We also need to know what features need to change to make the forests better suited to a new climate. Increasing the optimum temperature for carbon uptake is the top priority. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/582465/original/file-20240318-16-1k5k0h.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Peering inside the forest, looking through ferns and sedges at ground level and trees of various heights beneath the canopy" src="https://images.theconversation.com/files/582465/original/file-20240318-16-1k5k0h.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/582465/original/file-20240318-16-1k5k0h.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=409&fit=crop&dpr=1 600w, https://images.theconversation.com/files/582465/original/file-20240318-16-1k5k0h.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=409&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/582465/original/file-20240318-16-1k5k0h.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=409&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/582465/original/file-20240318-16-1k5k0h.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=514&fit=crop&dpr=1 754w, https://images.theconversation.com/files/582465/original/file-20240318-16-1k5k0h.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=514&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/582465/original/file-20240318-16-1k5k0h.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=514&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Beneath the canopy of the tallest trees there is a mid-layer of trees and a lower layer of ferns and sedges.</span>
<span class="attribution"><span class="source">Tim Wardlaw</span></span>
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</figure>
<h2>Producing climate-ready seed for sowing</h2>
<p>In new research, soon to be published, I reviewed several studies that compared the features of Tasmanian tall eucalypt forests with other forests on the Australian mainland. </p>
<p>I wanted to understand why Tasmania’s forests were so sensitive to heatwaves and what, if anything, could be done to lessen their impact. I found the poor response to heatwaves had more to do with the local conditions than anything else. The forests are accustomed to high rainfall and a narrow temperature range. </p>
<p>Could we speed up natural selection to help Tasmania’s tall eucalypt forests adapt to a new, warmer climate? </p>
<p>Previous research has shown forests can be managed to speed up natural selection and <a href="https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecm.1333">produce seed better suited to new climates</a>. But this is only feasible in forests managed for wood production. </p>
<p>We need to find out whether natural selection can increase the optimum temperature for carbon uptake by the forest, and if so, by how much. </p>
<p>We need to ensure the right policy settings are in place. A policy to end logging of native forests, for example, would rule out speeding up natural selection.</p>
<p>And we need to think and plan what to do if tall eucalypt forests in reserves are lost or irreparably damaged. Should we try to restore new generations of tall eucalypt forests, and if so, how?</p>
<p>Finally, community support is required. People need to understand what we are trying to achieve. They can also bring new ideas about how to make tall eucalypt forests more resilient. </p>
<p>Timely, accurate, trusted, and accessible information will be crucial. Ongoing <a href="https://www.tern.org.au/tern-ecosystem-processes/warra-tall-eucalypt-supersite/">monitoring</a> of the tall eucalypt forest in the upper reaches of Tasmania’s Huon Valley can provide much of this information.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/582464/original/file-20240318-18-dzlsif.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Aerial view of the Warra landscape looking looking south from the Warra flux tower above the canopy" src="https://images.theconversation.com/files/582464/original/file-20240318-18-dzlsif.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/582464/original/file-20240318-18-dzlsif.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/582464/original/file-20240318-18-dzlsif.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/582464/original/file-20240318-18-dzlsif.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/582464/original/file-20240318-18-dzlsif.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/582464/original/file-20240318-18-dzlsif.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/582464/original/file-20240318-18-dzlsif.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Warra Supersite in the upper reaches of the Huon Valley is one of 16 intensive ecosystem monitoring field stations in Australia’s Terrestrial Ecosystem Research Network.</span>
<span class="attribution"><span class="source">Michael Brown, ComStar Systems</span></span>
</figcaption>
</figure>
<h2>Future forests</h2>
<p>Clearly, humanity must cut greenhouse gas emissions and limit global warming. But some climate impacts are now unavoidable and we need to be prepared.</p>
<p>As heatwaves intensify, Tasmania’s tall eucalypt forests will reach a tipping point. Trees will die. The forest we know today will be lost forever. </p>
<p>But if we are prepared, we can ensure another forest takes its place. With our help, future generations of tall eucalypt forests can still exist – forests better suited to Tasmania’s new climate.</p>
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<p>
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<strong>
Read more:
<a href="https://theconversation.com/hard-to-kill-heres-why-eucalypts-are-survival-experts-222743">Hard to kill: here's why eucalypts are survival experts</a>
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<img src="https://counter.theconversation.com/content/224335/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>I receive funding from the Terrestrial Ecosystem Research Network.</span></em></p>Our tallest trees are world champions when it comes to capturing and storing carbon, but they don’t like the heat. Climate change will trigger mass tree deaths in Tasmania. Here’s what can be done.Tim Wardlaw, Research Associate, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2072192023-06-15T06:56:55Z2023-06-15T06:56:55ZOceans absorb 30% of our emissions, driven by a huge carbon pump. Tiny marine animals are key to working out its climate impacts<figure><img src="https://images.theconversation.com/files/531908/original/file-20230614-28-ritl1a.png?ixlib=rb-1.1.0&rect=12%2C1%2C894%2C598&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Julian Uribe-Palomino/IMOS-CSIRO</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The ocean holds 60 times more carbon than the atmosphere and absorbs almost 30% of carbon dioxide (CO₂) emissions from human activities. This means the ocean is key to understanding the global carbon cycle and thus our future climate. </p>
<p>The Intergovernmental Panel on Climate Change (IPCC) uses earth system models to project climate change. These projections inform critical political, social and technological decisions. However, if we can’t accurately model the marine carbon cycle then we cannot truly understand how Earth’s climate will respond to different emission scenarios. </p>
<p>In <a href="https://www.nature.com/articles/s43247-023-00871-w">research published today</a>, we show that zooplankton, tiny animals near the base of the ocean food chain, are likely to be the biggest source of uncertainty in how we model the marine carbon cycle. Getting their impact on the cycle right could add an extra 2 billion tonnes to current models’ assumptions about annual carbon uptake by the ocean. That’s more carbon than the entire global transportation sector emits.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/532100/original/file-20230615-22-8v22hr.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Graph showing global carbon budget with emissions and sinks" src="https://images.theconversation.com/files/532100/original/file-20230615-22-8v22hr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532100/original/file-20230615-22-8v22hr.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=590&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532100/original/file-20230615-22-8v22hr.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=590&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532100/original/file-20230615-22-8v22hr.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=590&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532100/original/file-20230615-22-8v22hr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=741&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532100/original/file-20230615-22-8v22hr.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=741&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532100/original/file-20230615-22-8v22hr.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=741&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The ocean (dark green) is a major carbon sink that partly offsets emissions in the global carbon budget.</span>
<span class="attribution"><a class="source" href="https://essd.copernicus.org/articles/14/4811/2022/">Global Carbon Budget 2022, Friedlingstein et al</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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Read more:
<a href="https://theconversation.com/oceans-are-better-at-storing-carbon-than-trees-in-a-warmer-future-ocean-carbon-sinks-could-help-stabilise-our-planet-176154">Oceans are better at storing carbon than trees. In a warmer future, ocean carbon sinks could help stabilise our planet</a>
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<h2>Marine carbon cycling is a $3 trillion thermostat</h2>
<p>Roughly <a href="https://essd.copernicus.org/articles/14/4811/2022/">10 billion tonnes</a> of carbon are being released into the atmosphere each year. But the ocean quickly absorbs about 3 billion tonnes of these emissions, leaving our climate cooler and more hospitable. If we <a href="https://www.ipcc.ch/sr15/chapter/chapter-2/">price carbon</a> at the rate the IPCC believes is needed to limit warming to 1.5°C, this adds up to over A$3 trillion worth of emission reductions accomplished naturally by the ocean every year. </p>
<p>However, we know the size of the ocean carbon sink has changed in the past, and even small changes can lead to big changes in the atmosphere’s temperature. Thus, we understand the ocean acts as a thermostat for our climate. But what controls the dial? </p>
<p>Extensive <a href="https://www.nature.com/articles/35038000">geological evidence</a> suggests microscopic marine life could be in control. Phytoplankton photosynthesise and consume <a href="https://www.nature.com/articles/483S17a#:%7E:text=Although%20they%20account%20for%20less,world's%20land%20plants%20combined2.">as much CO₂ as all land plants</a>. </p>
<p>When phytoplankton die, they sink and trap much of their carbon deep in the ocean. It can remain there for centuries to millennia, locked away safely out of contact with the atmosphere. </p>
<p>Any changes to the strength of this biological carbon pump will be felt in the atmosphere and <a href="https://scitechdaily.com/little-known-microbes-could-be-an-early-warning-signal-of-climate-tipping-point/">will change our climate</a>. Some have even proposed enhancing this biological pump by artificially fertilising the ocean with iron to stimulate phytoplankton. It’s possible this could sequester as much as an extra 20% of our annual CO₂ emissions. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/531909/original/file-20230614-17-p7rifi.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="The marine biological carbon pump" src="https://images.theconversation.com/files/531909/original/file-20230614-17-p7rifi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/531909/original/file-20230614-17-p7rifi.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=689&fit=crop&dpr=1 600w, https://images.theconversation.com/files/531909/original/file-20230614-17-p7rifi.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=689&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/531909/original/file-20230614-17-p7rifi.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=689&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/531909/original/file-20230614-17-p7rifi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=866&fit=crop&dpr=1 754w, https://images.theconversation.com/files/531909/original/file-20230614-17-p7rifi.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=866&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/531909/original/file-20230614-17-p7rifi.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=866&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A diagram of the natural biological carbon pump and how iron fertilisation could artificially enhance it.</span>
<span class="attribution"><a class="source" href="https://www.nature.com/articles/s43247-023-00871-w">Rohr et al (2019)</a>, <span class="license">Author provided</span></span>
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<p>
<em>
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Read more:
<a href="https://theconversation.com/smoke-from-the-black-summer-fires-created-an-algal-bloom-bigger-than-australia-in-the-southern-ocean-164564">Smoke from the Black Summer fires created an algal bloom bigger than Australia in the Southern Ocean</a>
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<h2>Right for the wrong reasons</h2>
<p>Despite its <a href="https://scitechdaily.com/little-known-microbes-could-be-an-early-warning-signal-of-climate-tipping-point/">importance for the global climate</a> and food production, there are large gaps in our understanding of how the marine carbon cycle is expected to change. Most earth system models differ in how the cycle’s major components will respond to a changing climate. Models simply can’t agree on what will happen to:</p>
<ul>
<li><p>net primary production – the carbon consumed by phytoplankton resulting in growth of marine plants at the base of the food web</p></li>
<li><p>secondary production – zooplankton growth, which is an indicator for fisheries, since fish eat zooplankton</p></li>
<li><p>export production – the biological pump of carbon transferred to the deep sea. </p></li>
</ul>
<p>To diagnose what might be going wrong, we compared the marine carbon cycle in 11 IPCC earth system models. We found the largest source of uncertainty is how fast zooplankton consume their phytoplankton prey, known as grazing pressure. </p>
<p>Models differ hugely in their assumptions about this grazing pressure. Even if zooplankton were exposed to the exact same amount of phytoplankton, the highest assumed grazing rate would be almost 100 times as fast as the slowest rate.</p>
<p>This is because some models effectively assume the ocean is filled entirely with slow-grazing shrimp. Others assume it is teeming exclusively with microscopic, but rapidly grazing <a href="https://www.britannica.com/science/ciliate">ciliates</a>. In reality, neither is true. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/531912/original/file-20230614-24-99hkpp.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/531912/original/file-20230614-24-99hkpp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/531912/original/file-20230614-24-99hkpp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=507&fit=crop&dpr=1 600w, https://images.theconversation.com/files/531912/original/file-20230614-24-99hkpp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=507&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/531912/original/file-20230614-24-99hkpp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=507&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/531912/original/file-20230614-24-99hkpp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=638&fit=crop&dpr=1 754w, https://images.theconversation.com/files/531912/original/file-20230614-24-99hkpp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=638&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/531912/original/file-20230614-24-99hkpp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=638&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Differences in prominent models’ estimates of the amount of zooplankton at different latitudes.</span>
<span class="attribution"><a class="source" href="https://www.nature.com/articles/s43247-023-00871-w">Adapted from Rohr et al (2023)</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
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<strong>
Read more:
<a href="https://theconversation.com/tiny-plankton-drive-processes-in-the-ocean-that-capture-twice-as-much-carbon-as-scientists-thought-136599">Tiny plankton drive processes in the ocean that capture twice as much carbon as scientists thought</a>
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<p>Models must make up for such large differences in zooplankton grazing by making additional assumptions about how fast phytoplankton grow and how quickly zooplankton die. Together, these differences can be balanced in a way that allows most models to simulate the present-day amount of carbon consumed by phytoplankton and transferred to the deep sea. </p>
<p>However, that is only because we can observe what those values should be. We can then tune models until we ensure they get the right answer. </p>
<p>Yet, even though our best models can admirably recreate the present-day ocean, they do so for different reasons and with dramatically different assumptions about the role of zooplankton. This means these models are built with fundamentally different machinery. When used to test future emissions scenarios, they will project fundamentally different outcomes. </p>
<p>We cannot know which projections are correct unless we know the true role of zooplankton. </p>
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Read more:
<a href="https://theconversation.com/climate-modelling-micro-algae-to-better-understand-the-workings-of-the-ocean-204412">Climate: modelling micro-algae to better understand the workings of the ocean</a>
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<h2>Tiny plankton with a big impact</h2>
<p>We ran a sensitivity experiment to show how small changes in zooplankton grazing can dramatically alter marine carbon cycling. We considered two sets of experiments, one control and one in which we increased both zooplankton grazing rates and phytoplankton growth rates, such that both were tuned to the exact same total carbon consumption by phytoplankton. </p>
<p>This increase in how fast zooplankton can graze was only a fraction of the difference between assumed grazing rates seen across IPCC models. Despite this, we found even this small increase led to a huge difference in the percentage of carbon consumed by phytoplankton that was eventually exported to depth and transferred up the food chain. </p>
<p>Ocean carbon storage increased by 2 billion tonnes per year. Zooplankton carbon consumption increased by 5 billion tonnes. </p>
<p>From a climate perspective, that is double the maximum theoretical potential of iron fertilisation. From a fisheries perspective, that leads to a 50% increase in the size of the global zooplankton population on which many fish feed. This matters for global food supply as the ocean feeds 10% of the global population.</p>
<p>This work shows we must improve both our understanding and modelling of zooplankton. With limited resources and an immense ocean, we will never have enough observations to build perfect models. However, new technologies for measuring zooplankton are making it easier to make autonomous, high-resolution measurements of many important variables. </p>
<p>We must make a concerted effort to leverage these new technologies to better understand the role of zooplankton in the marine carbon cycle. We will then be able to reduce uncertainties about future climate states, advance our ability to assess marine-based CO₂ removal, and improve global fisheries projections.</p><img src="https://counter.theconversation.com/content/207219/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Anthony Richardson receives funding from the Australian Research Council Discovery Project DP230102359 and Australia’s Integrated Marine Observing System (IMOS) enabled by the National Collaborative Research Infrastructure Strategy (NCRIS). </span></em></p><p class="fine-print"><em><span>Elizabeth Shadwick receives funding from Australian Government's Antarctic Science Collaboration Initiative, and Australia’s Integrated Marine Observing System (IMOS) enabled by the National Collaborative Research Infrastructure Strategy (NCRIS).</span></em></p><p class="fine-print"><em><span>Tyler Rohr does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Marine life known as zooplankton might be the biggest problem with getting carbon cycling right in climate models. The potential variations in carbon uptake are greater than global transport emissions.Tyler Rohr, Lecturer in Southern Ocean Biogeochemical Modelling, IMAS, University of TasmaniaAnthony Richardson, Professor, The University of QueenslandElizabeth Shadwick, Team Leader, Oceans & Atmosphere, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2066742023-06-05T20:03:27Z2023-06-05T20:03:27ZHidden carbon: Fungi and their ‘necromass’ absorb one-third of the carbon emitted by burning fossil fuels every year<figure><img src="https://images.theconversation.com/files/529991/original/file-20230605-28427-m0nvgp.jpg?ixlib=rb-1.1.0&rect=4%2C7%2C1592%2C1190&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mycorrhizal fungi growing with a plant root </span> <span class="attribution"><span class="source">Dr Yoshihiro Kobae</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Beneath our feet, remarkable networks of fungal filaments stretch out in all directions. These mycorrhizal fungi live in partnership with plants, offering nutrients, water and protection from pests in exchange for carbon-rich sugars.</p>
<p>Now, <a href="https://doi.org/10.1016/j.cub.2023.02.027">new research</a> shows this single group of fungi may quietly be playing a <a href="https://www.nature.com/articles/s41467-019-13019-2">bigger role in storing carbon</a> than we thought. </p>
<p>How much bigger? These microscopic filaments take up the equivalent of more than a third (36%) of the world’s annual carbon emissions from fossil fuels – every year.</p>
<p>As we search for ways to slow or stop the climate crisis, we often look to familiar solutions: cutting fossil fuel use, switching to renewables and restoring forests. This research shows we need to look down too, into our soils. </p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/529280/original/file-20230531-27-17lt2b.gif?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/529280/original/file-20230531-27-17lt2b.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/529280/original/file-20230531-27-17lt2b.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/529280/original/file-20230531-27-17lt2b.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/529280/original/file-20230531-27-17lt2b.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/529280/original/file-20230531-27-17lt2b.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/529280/original/file-20230531-27-17lt2b.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This shows how mycorrhizal fungi (fine white filaments) connect to plant root systems (yellow) and out into the soil.</span>
<span class="attribution"><span class="source">Scivit/Wikipedia</span></span>
</figcaption>
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<h2>This fungi-plant partnership is 400 million years old</h2>
<p>Mycorrhizal fungi are hard to spot, but their effects are startling. They thread networks of microscopic filaments through the soil and into the roots of almost every plant on earth. </p>
<p>But this is no hostile takeover. They’ve been partnering with plants for <a href="https://nph.onlinelibrary.wiley.com/doi/full/10.1046/j.1469-8137.2002.00397.x">more than 400 million years</a>. The length of these complex relationships has given them a <a href="https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.13288">vital role</a> in our ecosystems. </p>
<p>Sometimes fungi take more than they give. But often, these are relationships of <a href="https://www.science.org/doi/full/10.1126/science.1208473">mutual benefit</a>. Through their network, the fungi transport essential nutrients and water to plants, and can even boost their <a href="https://doi.org/10.1111/nph.17781">resistance to pests and disease</a>. </p>
<p>In return, plants pump sugars and fat made by photosynthesis in their leaves down through their roots to the fungi. These compounds are rich in carbon, taken from the atmosphere.</p>
<h2>How do these fungi fit into the carbon cycle?</h2>
<p>On land, the natural carbon cycle involves a delicate balance. Plants take CO₂ from the atmosphere through photosynthesis, while other organisms emit it back into the atmosphere. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/529486/original/file-20230601-22265-hn60tq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/529486/original/file-20230601-22265-hn60tq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=671&fit=crop&dpr=1 600w, https://images.theconversation.com/files/529486/original/file-20230601-22265-hn60tq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=671&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/529486/original/file-20230601-22265-hn60tq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=671&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/529486/original/file-20230601-22265-hn60tq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=844&fit=crop&dpr=1 754w, https://images.theconversation.com/files/529486/original/file-20230601-22265-hn60tq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=844&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/529486/original/file-20230601-22265-hn60tq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=844&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Carbon is captured by plants through photosynthesis, some of this carbon then goes into the networks of mycorrhizal fungi. These fungi also will release some of this carbon as CO₂ and as compounds into the soil.</span>
<span class="attribution"><span class="source">Adam Frew/Author provided using BioRender</span></span>
</figcaption>
</figure>
<p>Now we know the carbon transfer from plants to mycorrhizal fungi isn’t a side note – it’s a substantial part of this equation. </p>
<p>By analysing almost 200 datasets, the researchers estimate the world’s plants are transferring a staggering 3.58 billion tonnes of carbon per year to this underground network. That’s the same as 13.12 billion tonnes of CO₂ – more than a third of the world’s 36.3 billion tonnes of CO₂ emitted yearly by <a href="https://www.iea.org/reports/global-energy-review-co2-emissions-in-2021-2">burning fossil fuels</a>.</p>
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<em>
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Read more:
<a href="https://theconversation.com/do-trees-really-stay-in-touch-via-a-wood-wide-web-heres-what-the-evidence-says-199806">Do trees really stay in touch via a 'wood-wide web'? Here's what the evidence says</a>
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<p>To be clear, fungal carbon doesn’t present a climate solution by itself. It’s a missing piece in the carbon cycle puzzle. </p>
<p>We still have big gaps in data from particular ecosystems and geographic regions. For instance, this study didn’t have any data of this kind from Australia or Southeast Asia – because it doesn’t yet exist.</p>
<figure class="align-center ">
<img alt="Microscope image of plant roots that have been stained to show the mycorrhizal fungal inside the root of a plant." src="https://images.theconversation.com/files/529276/original/file-20230531-25-4m3nnt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/529276/original/file-20230531-25-4m3nnt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=241&fit=crop&dpr=1 600w, https://images.theconversation.com/files/529276/original/file-20230531-25-4m3nnt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=241&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/529276/original/file-20230531-25-4m3nnt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=241&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/529276/original/file-20230531-25-4m3nnt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=303&fit=crop&dpr=1 754w, https://images.theconversation.com/files/529276/original/file-20230531-25-4m3nnt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=303&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/529276/original/file-20230531-25-4m3nnt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=303&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This image shows mycorrhizal fungi (blue) growing inside plant roots, where they obtain carbon and provide plants with access to resources such as nutrients.</span>
<span class="attribution"><span class="source">Adam Frew</span></span>
</figcaption>
</figure>
<h2>What does this mean for the climate?</h2>
<p>We already know mycorrhizal fungi help soils retain carbon by releasing <a href="https://doi.org/10.1111/j.1574-6941.2007.00337.x">specific chemical compounds</a>. These compounds contain carbon and nitrogen. Once in the soil, these compounds can be used by other soil microorganisms, such as bacteria. When this happens it helps to form a highly stable soil carbon store that is more resistant to breakdown, and this store can accumulate <a href="https://doi.org/10.1111/nph.18914">more than four times faster</a> in the presence of mycorrhizal fungi.</p>
<p>When these fungi die, they leave behind “necromass” – a complex scaffold of dead organic material which can be stored in soil, and often inside clumps of soil particles. The carbon inside these clumps can stay in the soil for <a href="https://doi.org/10.2136/sssaj1994.03615995005800040023x">close to a decade</a> without being released back to the atmosphere.</p>
<p>In fact, other studies suggest this fungal necromass might <a href="https://doi.org/10.1016/j.soilbio.2021.108422">contribute more</a> to the carbon content of soil than living fungi.</p>
<p>But these fungi also naturally cause carbon to escape back <a href="https://doi.org/10.1146/annurev-ecolsys-110617-062331">to the atmosphere</a> by decomposing organic matter or changing water and nutrient availability, which influences how other organisms decompose. Mycorrhizal fungi also release some carbon back into the atmosphere, though the rate this happens <a href="https://doi.org/10.1016/j.soilbio.2021.108454">depends on many factors</a>. </p>
<p>What does this mean for climate change? While atmospheric CO₂ concentrations keep rising, it doesn’t necessarily mean fungi are storing more of it. Recent research in an <a href="https://doi.org/10.1038/s41586-020-2128-9">Australian woodland</a> found higher atmospheric CO₂ did see more carbon sent below the ground. But this carbon wasn’t stored for long periods. </p>
<p>To date, mycorrhizal fungi have been poorly represented in global carbon cycle models. They aren’t often considered when assessing which species are <a href="https://doi.org/10.1002/ppp3.10146">at risk of extinction</a> or <a href="https://doi.org/10.1111/rec.13866">promoting successful restorations</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/529473/original/file-20230531-22265-5nd0xx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/529473/original/file-20230531-22265-5nd0xx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/529473/original/file-20230531-22265-5nd0xx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/529473/original/file-20230531-22265-5nd0xx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/529473/original/file-20230531-22265-5nd0xx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/529473/original/file-20230531-22265-5nd0xx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/529473/original/file-20230531-22265-5nd0xx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">We need more research to better understand the role of mycorrhizal fungi in the carbon cycle across different ecosystems, including in agriculture.</span>
<span class="attribution"><span class="source">Dylan de Jonge/Unsplash</span></span>
</figcaption>
</figure>
<h2>Protecting our fungal networks</h2>
<p>When we cut down forests or clear land, we not only disrupt life above the ground, but <a href="https://doi.org/10.1111/gcb.12565">underground as well</a>. We need to safeguard these hidden fungal networks which give our plants resilience – and play a key role in the carbon cycle. </p>
<p>As we better understand how these fungi work and what we’re doing to them, we can also develop farming methods which better preserve them and their carbon. </p>
<p>As <a href="https://www.spun.earth/">global</a> and <a href="https://www.digupdirt.net/">Australian initiatives</a> continue to map the diversity of mycorrhizal fungi, scientists are working to understand what <a href="https://doi.org/10.1111/1365-2435.14349">shapes these communities</a> and <a href="https://doi.org/10.1111/nph.15119">their roles</a>. </p>
<p>We’ve long overlooked these vital lifeforms. But as we learn more about how fungi and plants cooperate and store carbon, it’s well past time for that to change. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-secret-life-of-fungi-how-they-use-ingenious-strategies-to-forage-underground-156610">The secret life of fungi: how they use ingenious strategies to forage underground</a>
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</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/206674/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adam Frew receives funding from the Australian Research Council, the British Ecological Society, and the Ecological Society of Australia.</span></em></p><p class="fine-print"><em><span>Jeff Powell receives funding from the Australian Research Council and NSW State Government. </span></em></p><p class="fine-print"><em><span>Carlos Aguilar-Trigueros and Natascha Weinberger do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>New research about underground fungal filaments suggests these networks store a vast amount of carbon. All the more reason to preserve them.Adam Frew, Lecturer and ARC DECRA Fellow, Western Sydney UniversityCarlos Aguilar-Trigueros, Postdoctoral fellow, Western Sydney UniversityJeff Powell, Professor and ARC Future Fellow, Western Sydney UniversityNatascha Weinberger, Postdoctoral Research Fellow, Western Sydney UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2009012023-03-09T19:04:50Z2023-03-09T19:04:50ZA tonne of fossil carbon isn’t the same as a tonne of new trees: why offsets can’t save us<figure><img src="https://images.theconversation.com/files/514352/original/file-20230309-24-7ethaq.jpg?ixlib=rb-1.1.0&rect=20%2C53%2C4473%2C2937&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>This week, the Albanese government is <a href="https://www.aph.gov.au/Parliamentary_Business/Bills_Legislation/Bills_Search_Results/Result?bId=r6957">attempting to reform</a> the safeguard mechanism to try to make it actually cut emissions from our highest polluting industrial facilities. </p>
<p>Experts and commentators see Labor’s plan as a <a href="https://theconversation.com/labors-scheme-to-cut-industrial-emissions-is-worryingly-flexible-197525">cautious, incremental change</a> that doesn’t yet rise to the urgency of the intensifying climate crisis. But it could generate momentum after a wasted decade of climate denial and delay under the previous government. Done right, it could set our biggest industrial polluters on a pathway to cut their emissions and be a springboard for more ambitious changes.</p>
<p>But there’s one glaring problem. Under the government’s proposed rules, there is still no requirement for polluters to actually cut their emissions at the sites where they are released into the atmosphere. Instead, companies can choose to buy carbon credits or offsets to meet their obligations. Incredibly, there would be no limit on the number of offsets companies can use. </p>
<p>You’ve probably heard about Australia’s rubbery offset schemes and <a href="https://australiainstitute.org.au/post/the-safeguard-mechanism-explained/">questions of integrity</a>. But there’s an even more <a href="https://www.nature.com/articles/nclimate1804">fundamental problem</a>. One tonne of carbon dioxide pumped into the atmosphere by burning fossil fuels is not the same as one tonne of carbon stored in the tree trunks of a newly planted forest. </p>
<p>The carbon in coal, gas and oil has been safely stored underground for extraordinary lengths of time. But when trees take carbon dioxide back out of the atmosphere, they may only store it for a short period. </p>
<p>There is simply no way around it. Avoiding the worst of climate change means stopping the extraction and burning of fossil fuels. Offsets will not save us. In fact, unlimited use of offsets could see <a href="https://www.climatecouncil.org.au/resources/safeguard-mechanism-briefing-paper/">even more emissions</a>, if coal and gas companies “offset” emissions and ramp up exports. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/514357/original/file-20230309-177-t1qbal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="revegetation tubestock" src="https://images.theconversation.com/files/514357/original/file-20230309-177-t1qbal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/514357/original/file-20230309-177-t1qbal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/514357/original/file-20230309-177-t1qbal.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/514357/original/file-20230309-177-t1qbal.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/514357/original/file-20230309-177-t1qbal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/514357/original/file-20230309-177-t1qbal.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/514357/original/file-20230309-177-t1qbal.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">It sounds simple: offset emissions by replanting forests. It’s not.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Why can’t we rely on nature to pull carbon dioxide from the air?</h2>
<p>In 2023, many policymakers still believe we can adequately offset emissions. It would certainly be easier if we could keep burning fossil fuels and offsetting them by planting forests. But it doesn’t work. It’s simply <a href="https://climateanalytics.org/media/why_offsets_are_not_a_viable_alternative_to_cutting_emissions.pdf">not possible</a> to fully “offset” billions of tonnes of greenhouse gas emissions from burning of coal, oil and gas by regrowing forests, increasing the amount of carbon in soils or other measures. </p>
<p>That’s because the carbon dioxide released by burning fossil fuels is <a href="https://www.climatecouncil.org.au/uploads/aadc6ea123523a46102e2be45bfcedc8.pdf">fundamentally different</a> to the way carbon is stored above ground in trees, wetlands and in the soil. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/514353/original/file-20230309-20-h9ha7f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="coal seam in rock" src="https://images.theconversation.com/files/514353/original/file-20230309-20-h9ha7f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/514353/original/file-20230309-20-h9ha7f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/514353/original/file-20230309-20-h9ha7f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/514353/original/file-20230309-20-h9ha7f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/514353/original/file-20230309-20-h9ha7f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/514353/original/file-20230309-20-h9ha7f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/514353/original/file-20230309-20-h9ha7f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The only long term storage solution for fossil fuels like coal is to leave them precisely where they are.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Carbon is everywhere on Earth — in the atmosphere, the ocean, in soils, in all living things, and in rocks and sediments. It is constantly being cycled through these different parts. Carbon is also being continually exchanged between the atmosphere and the ocean’s surface. Together these processes make up the earth’s “active” carbon cycle. </p>
<p>When we burn fossil fuels, we release carbon locked away for millions of years (hence “fossil” fuels), pumping vast new volumes of carbon into the active carbon cycle. This is very clearly <a href="https://essd.copernicus.org/articles/14/4811/2022/">altering the balance</a> of carbon in the Earth system and faster than ever recorded in the Earth’s geological history. Planting trees does not lock carbon away again deep underground. Instead, the introduced fossil carbon remains part of the active carbon cycle.</p>
<p>To compound the problem, much of the carbon stored in land-based offsets does not stay stored. Forests can easily be destroyed by fire, disease, floods and droughts, all of which <a href="https://www.csiro.au/en/research/environmental-impacts/climate-change/climate-change-qa/impacts">are increasing</a> with climate change.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/514350/original/file-20230309-24-t1qbal.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="figure of carbon cycle" src="https://images.theconversation.com/files/514350/original/file-20230309-24-t1qbal.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/514350/original/file-20230309-24-t1qbal.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=418&fit=crop&dpr=1 600w, https://images.theconversation.com/files/514350/original/file-20230309-24-t1qbal.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=418&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/514350/original/file-20230309-24-t1qbal.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=418&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/514350/original/file-20230309-24-t1qbal.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=525&fit=crop&dpr=1 754w, https://images.theconversation.com/files/514350/original/file-20230309-24-t1qbal.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=525&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/514350/original/file-20230309-24-t1qbal.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=525&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Carbon is continually exchanged between the land and the atmosphere on timescales of seconds, days, decades and centuries, whereas fossil carbon has been locked away from the atmosphere for millions of years.</span>
<span class="attribution"><span class="source">Climate Council</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Offsets are a last resort – nothing more</h2>
<p>Despite these issues, offsets will still have a small role. Some emissions cannot be avoided or reduced at present, given low-emissions technologies for industries like steelmaking are still scaling up. But these offsets must be strictly limited and set to progressively decline over time, as opportunities for genuine emissions reductions – at the source – are developed and rapidly scaled. </p>
<p>Unfortunately, paying for offsets is the first and only thing many large companies are doing about their harmful emissions. </p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/the-greens-arent-grandstanding-on-a-new-coal-and-gas-ban-theyre-negotiating-well-201287">The Greens aren't grandstanding on a new coal and gas ban – they're negotiating well</a>
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<p>If we allow fossil fuel companies to offset their emissions without limit, they will keep along a business as usual track or even expand their operations. That, in turn, will mean significantly more emissions when Australian fossil fuels are burned overseas. </p>
<h2>Our leaders must avoid the offset trap</h2>
<p>It’s taken Australia decades too long, but we’re finally past climate denial, perhaps due to unprecedented fire and floods. Our leaders tell us it’s now about finding solutions. Well, offsets are not a solution. There is no substitute to actually ending the routine burning of fossil fuels. </p>
<p>We all want our comfortable lives to continue with a minimum of change. Offsets seem to deliver that. But all they really do is offset our guilt and responsibility. They cannot solve the central problem which is that every year, we add another <a href="https://www.iea.org/news/defying-expectations-co2-emissions-from-global-fossil-fuel-combustion-are-set-to-grow-in-2022-by-only-a-fraction-of-last-year-s-big-increase">33 billion</a> tonnes of carbon dioxide to the atmosphere by burning fossil fuels. </p>
<p>The atmosphere doesn’t respond to good intentions or clever schemes. All it responds to is the volume of greenhouse gases which trap ever more heat. </p>
<p>If Labor is to make the safeguard mechanism fit for purpose, it must focus on <a href="https://www.climatecouncil.org.au/resources/submission-department-climate-change-energy-environment-and-water-consultation-proposed-design-safeguard-mechanism-reform/">genuine emissions reductions at the source</a>. </p>
<p>What Australia does matters a great deal to the world’s efforts to tackle the climate crisis. If Australia became the first major fossil fuel exporter to embrace a future as a clean energy superpower, it will demonstrate it is possible – and that it comes with benefits like new industries, cleaner air and energy security. </p>
<p>First, though, we have to give up on offset pipe dreams. The only thing that matters is cutting emissions. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/now-we-know-the-flaws-of-carbon-offsets-its-time-to-get-real-about-climate-change-181071">Now we know the flaws of carbon offsets, it's time to get real about climate change</a>
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<img src="https://counter.theconversation.com/content/200901/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Wesley Morgan is a senior researcher with the Climate Council. This article was drafted in collaboration with Climate Council senior researchers Simon Bradshaw and Ashleigh Croucher.</span></em></p>Labor must resist the false promise of carbon offsets in its safeguard mechanism. The only thing that matters is actually cutting emissionsWesley Morgan, Research Fellow, Griffith Asia Institute, Griffith UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1900672022-09-22T20:18:11Z2022-09-22T20:18:11ZTermites love global warming – the pace of their wood munching gets significantly faster in hotter weather<figure><img src="https://images.theconversation.com/files/484302/original/file-20220913-24-1p0v15.jpg?ixlib=rb-1.1.0&rect=6%2C0%2C1370%2C997&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Wood feeding termites (_Microcerotermes spp_) inside their nest. </span> <span class="attribution"><span class="source">Johan Larson</span>, <span class="license">Author provided</span></span></figcaption></figure><p>When we consider termites, we may think of the danger they can pose to our houses once they settle in and start eating wood. But in fact, only about <a href="https://australian.museum/learn/animals/insects/termites-as-pests/">4% of termite species</a> worldwide are considered pests that might, at some point, eat your house.</p>
<p>In nature, wood-eating termites play a broad and important role in warm tropical and sub-tropical ecosystems. In feeding on wood, they recycle essential nutrients to the soil and release carbon back to the atmosphere. </p>
<p>Our new research, <a href="https://www.science.org/doi/10.1126/science.abo3856">published today in Science</a>, quantified for the first time just how much termites love the warmth. The results are striking: we found termites eat deadwood much faster in warmer conditions. For example, termites in a region with temperatures of 30°C will eat wood seven times faster than in a place with temperatures of 20°C.</p>
<p>Our results also point to an expanding role for termites in the coming decades, as climate change increases their potential habitat across the planet. And this, in turn, could see more carbon stored in deadwood released into the atmosphere. </p>
<h2>Deadwood in the global carbon cycle</h2>
<p><a href="https://www.silvafennica.fi/article/244">Trees</a> play a pivotal role in the global carbon cycle. They absorb carbon dioxide from the atmosphere through photosynthesis, and roughly <a href="https://www.nature.com/articles/s41467-021-21149-9">half</a> of this carbon is incorporated into new plant mass. </p>
<p>While most <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.16100">trees</a> grow slowly in height and diameter each year, a small proportion die. Their remains then enter the deadwood pool. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/485501/original/file-20220920-17-9z7s5f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/485501/original/file-20220920-17-9z7s5f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/485501/original/file-20220920-17-9z7s5f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/485501/original/file-20220920-17-9z7s5f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/485501/original/file-20220920-17-9z7s5f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/485501/original/file-20220920-17-9z7s5f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/485501/original/file-20220920-17-9z7s5f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/485501/original/file-20220920-17-9z7s5f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Termites and microbes release the carbon stored in deadwood into the atmosphere.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Here carbon accumulates, until the deadwood is either <a href="https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2009.01916.x">burned or decayed</a> through consumption by microbes (fungi and bacteria), or insects such as termites. </p>
<p>If the deadwood pool is consumed quickly, then the carbon stored there will rapidly be released back to the atmosphere. But if decay is slow, then the size of deadwood pool can increase, slowing the accumulation of carbon dioxide and methane in the atmosphere.</p>
<p>For this reason, understanding the dynamics of the community of organisms that decay deadwood is vital, as it can help scientists predict the impacts of climate change on the carbon stored in land ecosystems. </p>
<p>This is important as releasing deadwood carbon to the atmosphere could speed up the pace of climate change. Storing it for longer could slow climate change down. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/decaying-forest-wood-releases-a-whopping-10-9-billion-tonnes-of-carbon-each-year-this-will-increase-under-climate-change-164406">Decaying forest wood releases a whopping 10.9 billion tonnes of carbon each year. This will increase under climate change</a>
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<h2>Testing how fast termites eat deadwood</h2>
<p>Scientists generally understand the conditions that favour microbes’ consumption of deadwood. We know their activity typically <a href="https://link.springer.com/article/10.1186/s13021-019-0136-6">doubles</a> with each 10°C increase in temperature. Microbial decay of deadwood is also typically faster in moist conditions. </p>
<p>On the other hand, scientists knew relatively little about the global distribution of deadwood-eating termites, or how this distribution would respond to different temperatures and moisture levels in different parts of the world. </p>
<p>To better understand this, we first developed a protocol for assessing termite consumption rates of deadwood, and tested it in a savannah and a rainforest ecosystem <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/aec.12561">in northeast Queensland</a>. </p>
<p>Our method involved placing a series of mesh-covered wood blocks on the soil surface in a few locations. Half the blocks had small holes in the mesh, giving termites access. The other half didn’t have such holes, so only microbes could access the blocks through the mesh.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/484298/original/file-20220913-20-q0dwnp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/484298/original/file-20220913-20-q0dwnp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/484298/original/file-20220913-20-q0dwnp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/484298/original/file-20220913-20-q0dwnp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/484298/original/file-20220913-20-q0dwnp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/484298/original/file-20220913-20-q0dwnp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/484298/original/file-20220913-20-q0dwnp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A block of pine wood wrapped to keep out termites and left in the forest to decompose.</span>
</figcaption>
</figure>
<p>We collected wood blocks every six months and found the blocks covered by mesh with holes decayed faster than those without, meaning the contribution of termites to this decay was, in fact, significant. </p>
<p>But while the test run told us about termites in Queensland, it didn’t tell us what they might do elsewhere. Our next step was to reach out to colleagues who could deploy the wood block protocol at their study sites around the world, and they enthusiastically took up the invitation.</p>
<p>In the end, more than 100 collaborators joined the effort at more than 130 sites in a variety of habitats, spread across six continents. This broad coverage let us assess how wood consumption rates by termites varied with climatic factors, such as mean annual temperature and rainfall.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/484307/original/file-20220913-24-poq313.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/484307/original/file-20220913-24-poq313.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/484307/original/file-20220913-24-poq313.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/484307/original/file-20220913-24-poq313.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/484307/original/file-20220913-24-poq313.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/484307/original/file-20220913-24-poq313.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/484307/original/file-20220913-24-poq313.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Amy Zanne with graduate student Mariana Nardi and postdoctoral fellow Paulo Negri from Universidade Estadual de Campinas near termite mounds in tropical cerrado savanna in Chapada dos Veadieros National Park. Photo by Rafael Oliveira.</span>
</figcaption>
</figure>
<h2>Termites love the warmth, and not too much rain</h2>
<p>For the wood blocks accessible to only microbes, we confirmed what scientists already knew – that decay rates approximately doubled across sites for each 10°C increase in mean annual temperature. Decay rates further increased when sites had higher annual rainfall, such as in Queensland’s rainforests. </p>
<p>For the termites’ wood blocks, we observed a much steeper relationship between decay rates and temperature – deadwood generally decayed almost seven times faster at sites that were 10°C hotter than others.</p>
<p>To put this in context, termite activity meant wood blocks near tropical Darwin at the northern edge of Australia decayed more than ten times faster than those in temperate Tasmania. </p>
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<p>
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<p>Our analyses also showed termite consumption of the wood blocks was highest in warm areas with low to intermediate mean annual rainfall. For example, termite decay was five times faster in a sub-tropical desert in South Africa than in a tropical rainforest in Puerto Rico.</p>
<p>This might be because termites safe in their mounds are able to access water deep in the soil in dry times, while waterlogging can limit their ability to forage for deadwood.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/485500/original/file-20220920-17-ppvp23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/485500/original/file-20220920-17-ppvp23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/485500/original/file-20220920-17-ppvp23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/485500/original/file-20220920-17-ppvp23.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/485500/original/file-20220920-17-ppvp23.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/485500/original/file-20220920-17-ppvp23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/485500/original/file-20220920-17-ppvp23.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/485500/original/file-20220920-17-ppvp23.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Termites thrive in hot, dry climates.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Termites and climate change</h2>
<p>Our results were synthesised in a model to predict how termite consumption of deadwood might change globally in response to climate change.</p>
<p>Over the coming decades, we predict greater termite activity as climate change projections show suitable termite habitat will expand north and south of the equator. </p>
<p>This will mean carbon cycling through the deadwood pool will get faster, returning carbon dioxide fixed by trees to the atmosphere, which could limit the storage of carbon in these ecosystems. Reducing the amount of carbon stored on land could then start a feedback loop to accelerate the pace of climate change.</p>
<p>We have long known human-caused climate change would favour a few winners but leave many losers. It would appear the humble termite is likely to be one such winner, about to experience a significant global expansion in its prime habitat.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/my-formula-for-a-tasty-and-nutritious-nigerian-soup-with-termites-171254">My formula for a tasty and nutritious Nigerian soup – with termites</a>
</strong>
</em>
</p>
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<img src="https://counter.theconversation.com/content/190067/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alexander William Cheesman receives funding from the Australian Research Council and UK's National Environmental Research Council. </span></em></p><p class="fine-print"><em><span>Amy Zanne receives funding from the US National Science Foundation. She is affiliated with the New Phytologist Foundation and Restor Foundation. </span></em></p><p class="fine-print"><em><span>Lucas Cernusak receives funding from the Australian Research Council. </span></em></p>Termites are about to experience a significant global expansion in their prime habitat, thanks to climate change. Here’s what that means for deadwood.Alexander Cheesman, Senior Research Fellow, James Cook UniversityAmy Zanne, Professor in Biology and Aresty Chair in Tropical Ecology, University of MiamiLucas Cernusak, Associate Professor, Plant Physiology, James Cook UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1837252022-05-25T20:16:48Z2022-05-25T20:16:48ZHow plate tectonics, mountains and deep-sea sediments have maintained Earth’s ‘Goldilocks’ climate<p>For hundreds of millions of years, Earth’s climate has warmed and cooled with natural fluctuations in the level of carbon dioxide (CO₂) in the atmosphere. Over the past century, <a href="https://theconversation.com/humanity-is-compressing-millions-of-years-of-natural-change-into-just-a-few-centuries-170525">humans have pushed CO₂ levels</a> to their highest in 2 million years – <a href="https://www.sciencedirect.com/science/article/pii/S1674927818300376">overtaking natural emissions</a> – mostly by burning fossil fuels, causing ongoing global warming that may make parts of the globe uninhabitable.</p>
<p>What can be done? As Earth scientists, we look to how natural processes have recycled carbon from atmosphere to Earth and back in the past to find possible answers to this question.</p>
<p>Our <a href="https://www.nature.com/articles/s41586-022-04420-x">new research</a> published in Nature, shows how tectonic plates, volcanoes, eroding mountains and seabed sediment have controlled Earth’s climate in the geological past. Harnessing these processes may play a part in maintaining the “<a href="https://www.abc.net.au/news/science/2016-02-22/goldilocks-zones-habitable-zone-astrobiology-exoplanets/6907836">Goldilocks</a>” climate our planet has enjoyed.</p>
<h2>From hothouse to ice age</h2>
<p><a href="https://theconversation.com/we-are-heading-for-the-warmest-climate-in-half-a-billion-years-says-new-study-73648">Hothouse and icehouse climates</a> have existed in the geological past. The Cretaceous hothouse (which lasted from roughly 145 million to 66 million years ago) had atmospheric CO₂ levels above 1,000 parts per million, compared with around 420 today, and temperatures up to 10°C higher than today. </p>
<p>But Earth’s climate began to <a href="https://www.eurekalert.org/news-releases/911139">cool around 50 million years ago</a> during the <a href="https://www.geosociety.org/GSA/Education_Careers/Geologic_Time_Scale/GSA/timescale/home.aspx">Cenozoic Era</a>, culminating in an <a href="https://theconversation.com/the-last-ice-age-tells-us-why-we-need-to-care-about-a-2-change-in-temperature-126923">icehouse climate</a> in which temperatures dropped to roughly 7°C cooler than today.</p>
<p>What kickstarted this dramatic change in global climate?</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/465011/original/file-20220524-16-e0esr2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/465011/original/file-20220524-16-e0esr2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=196&fit=crop&dpr=1 600w, https://images.theconversation.com/files/465011/original/file-20220524-16-e0esr2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=196&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/465011/original/file-20220524-16-e0esr2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=196&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/465011/original/file-20220524-16-e0esr2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=246&fit=crop&dpr=1 754w, https://images.theconversation.com/files/465011/original/file-20220524-16-e0esr2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=246&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/465011/original/file-20220524-16-e0esr2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=246&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Earth evolved from a hothouse climate in the Cretaceous Period (left) to an icehouse climate in the following Cenozoic Era (right), leading to inland ice sheets.</span>
<span class="attribution"><span class="source">F. Guillén and M. Antón / Wikimedia commons</span></span>
</figcaption>
</figure>
<p>Our suspicion was that Earth’s tectonic plates were the culprit. To better understand how tectonic plates store, move and emit carbon, we built a computer model of the tectonic “carbon conveyor belt”.</p>
<h2>The carbon conveyor belt</h2>
<p>Tectonic processes release carbon into the atmosphere at mid-ocean ridges - where two plates are moving away from each other - allowing magma to rise to the surface and create new ocean crust.</p>
<p>At the same time, at ocean trenches - where two plates converge - plates are pulled down and recycled back into the deep Earth. On their way down they carry carbon back into the Earth’s interior, but also release some CO₂ via volcanic activity. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/465207/original/file-20220525-24-pj1cjh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/465207/original/file-20220525-24-pj1cjh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=264&fit=crop&dpr=1 600w, https://images.theconversation.com/files/465207/original/file-20220525-24-pj1cjh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=264&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/465207/original/file-20220525-24-pj1cjh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=264&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/465207/original/file-20220525-24-pj1cjh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=331&fit=crop&dpr=1 754w, https://images.theconversation.com/files/465207/original/file-20220525-24-pj1cjh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=331&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/465207/original/file-20220525-24-pj1cjh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=331&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Earth’s tectonic carbon conveyor belt shifts massive amounts of carbon between the deep Earth and the surface, from mid-ocean ridges to subduction zones, where oceanic plates carrying deep-sea sediments are recycled back into the Earth’s interior. The processes involved play a pivotal role in Earth’s climate and habitability.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>Our model shows that the Cretaceous hothouse climate was caused by very fast-moving tectonic plates, which dramatically increased CO₂ emissions from mid-ocean ridges. </p>
<p>In the transition to the Cenozoic icehouse climate tectonic plate movement slowed down and volcanic CO₂ emissions began to fall. But to our surprise, we discovered a more complex mechanism hidden in the conveyor belt system involving mountain building, continental erosion and burial of the remains of miscroscopic organisms on the seafloor.</p>
<h2>The hidden cooling effect of slowing tectonic plates in the Cenozoic</h2>
<p>Tectonic plates slow down due to collisions, which in turn leads to mountain building, such as the Himalayas and the Alps formed over the last 50 million years. This should have reduced volcanic CO₂ emissions but instead our carbon conveyor belt model revealed increased emissions. </p>
<p>We tracked their source to carbon-rich deep-sea sediments being pushed downwards to feed volcanoes, increasing CO₂ emissions and cancelling out the effect of slowing plates. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/waGHSfs_YRg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">This video shows plate motions, carbon storage within tectonic plates and carbon degassing along mid-ocean ridges and subduction zones through time. Our carbon model shows these processes alone cannot explain global cooling in the Cenozoic Era. The effects of rock erosion, not shown here, played a key role. Arrows indicate plate motion speed.</span></figcaption>
</figure>
<p>So what exactly was the mechanism responsible for the drop in atmospheric CO₂? </p>
<p>The answer lies in the mountains that were responsible for slowing down the plates in the first place and in carbon storage in the deep sea. </p>
<p>As soon as mountains form, they start being eroded. Rainwater containing CO₂ reacts with a range of mountain rocks, breaking them down. Rivers carry the dissolved minerals into the sea. Marine organisms then use the dissolved products to build their shells, which ultimately become a part of carbon-rich marine sediments. </p>
<p>As new mountain chains formed, more rocks were eroded, speeding up this process. Massive amounts of CO₂ were stored away, and the planet cooled, even though some of these sediments were subducted with their carbon degassing via arc volcanoes.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/465016/original/file-20220524-21-77qtj5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Photographs showing white cliffs rising from the sea." src="https://images.theconversation.com/files/465016/original/file-20220524-21-77qtj5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/465016/original/file-20220524-21-77qtj5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=353&fit=crop&dpr=1 600w, https://images.theconversation.com/files/465016/original/file-20220524-21-77qtj5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=353&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/465016/original/file-20220524-21-77qtj5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=353&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/465016/original/file-20220524-21-77qtj5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=443&fit=crop&dpr=1 754w, https://images.theconversation.com/files/465016/original/file-20220524-21-77qtj5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=443&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/465016/original/file-20220524-21-77qtj5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=443&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The limestone of the White Cliffs of Dover is an example of carbon-rich marine sediment, composed of the remains of tiny calcium carbonate skeletons of marine plankton.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:White_Cliffs_of_Dover_02.JPG">I Giel / Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Rock weathering as a possible carbon dioxide removal technology</h2>
<p>The Intergovernmental Panel on Climate Change (IPCC) <a href="https://www.ipcc.ch/report/sixth-assessment-report-working-group-3/">says</a> large-scale deployment of carbon dioxide removal methods is “unavoidable” if the world is to reach net-zero greenhouse gas emissions.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/on-top-of-drastic-emissions-cuts-ipcc-finds-large-scale-co-removal-from-air-will-be-essential-to-meeting-targets-180663">On top of drastic emissions cuts, IPCC finds large-scale CO₂ removal from air will be "essential" to meeting targets</a>
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</p>
<hr>
<p>The weathering of igneous rocks, especially rocks like basalt containing a mineral called olivine, is very efficient in reducing atmospheric CO₂. Spreading olivine on beaches could <a href="https://www.theguardian.com/environment/2021/jun/23/cloud-spraying-and-hurricane-slaying-could-geoengineering-fix-the-climate-crisis">absorb up to a trillion tonnes of CO₂ from the atmosphere</a>, according to <a href="https://www.vesta.earth/">some estimates</a>. </p>
<p>The speed of current <a href="https://climate.nasa.gov/evidence/">human-induced warming</a> is such that reducing our carbon emissions very quickly is essential to avoid catastrophic global warming. But geological processes, with some human help, may also have their role in maintaining Earth’s “Goldilocks” climate.</p>
<hr>
<p><em>This study was carried out by researchers from the University of Sydney’s <a href="https://www.earthbyte.org/">EarthByte Group</a>, The University of Western Australia, the University of Leeds and the Swiss Federal Institute of Technology, Zurich using <a href="https://www.gplates.org">GPlates</a> open access modelling software. This was enabled by Australia’s National Collaborative Research Infrastructure Strategy (NCRIS) via <a href="https://www.auscope.org.au/">AuScope</a> and The Office of the Chief Scientist and Engineer, NSW Department of Industry.</em></p><img src="https://counter.theconversation.com/content/183725/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dietmar Müller receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Adriana Dutkiewicz receives funding from the Australian Research Council (FT190100829). </span></em></p><p class="fine-print"><em><span>Andrew Merdith receives funding from MSCA-IF project 893615. </span></em></p><p class="fine-print"><em><span>Christopher Gonzalez received funding from Australian Research Council. </span></em></p><p class="fine-print"><em><span>Sabin Zahirovic receives funding from the Australian Research Council (DE210100084). </span></em></p><p class="fine-print"><em><span>Tobias Keller previously received funding from the European Research Council and from the Swiss National Science Foundation.</span></em></p><p class="fine-print"><em><span>Weronika Gorczyk receives funding from Australian Research Council and Minerals Research Institute Of Western Australia</span></em></p><p class="fine-print"><em><span>Jo Condon is affiliated with AuScope, a federally funded and non-profit NCRIS organisation that supports the development of GPlates software used in the research described in this article.</span></em></p><p class="fine-print"><em><span>Ben Mather does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>New modelling shows how tectonic plate movements, carbon-rich deep-sea sediment, and mountain weathering have regulated Earth’s climate.Dietmar Müller, Professor of Geophysics, University of SydneyAdriana Dutkiewicz, ARC Future Fellow, University of SydneyAndrew Merdith, Research fellow, University of LeedsBen Mather, Research fellow, University of SydneyChristopher Gonzalez, Research Fellow, The University of Western AustraliaSabin Zahirovic, Postdoctoral Research Associate, University of SydneyTobias Keller, Senior Scientist in Computational Geosciences, Swiss Federal Institute of Technology ZurichWeronika Gorczyk, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1725052021-12-09T13:29:02Z2021-12-09T13:29:02ZCurious Kids: If steam contains water, what does smoke from fire contain?<figure><img src="https://images.theconversation.com/files/433661/original/file-20211124-25-p99tno.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Toa55/Shutterstock</span></span></figcaption></figure><p><em>Curious Kids is <a href="https://theconversation.com/africa/topics/curious-kids-36782">a series</a> for children in which we ask experts to answer questions from kids.</em></p>
<p><strong>If steam contains water, which goes up and evaporates, what does smoke from fire contain? (Amasi-Mario, 8, Nigeria)</strong></p>
<p>You’ve asked an important question, Amasi-Mario: this is something that lots of people around the world have also wondered. As a scientist <a href="http://archibaldlab.weebly.com/team.html">who studies</a> how fires happen in natural spaces like savannas and forests, and what they can do to the environment, I’m one of those people. </p>
<p>Living in Nigeria, you’ve probably seen lots of fires; some in your own home to keep you warm, and some burning through the bush. You will have noticed that not all fires make the same sort of smoke. There are a few reasons for this – let me explain. </p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption"></span>
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<p><em><a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a> is a series by <a href="https://theconversation.com/uk">The Conversation</a> that gives children the chance to have their questions about the world answered by experts. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskids@theconversation.com">curiouskids@theconversation.com</a>. We won’t be able to answer every question, but we’ll do our very best.</em></p>
<h2>What is in smoke</h2>
<p>When fires burn they are “consuming” plants. After a fire the vegetation that was there before has gone, and plants have to grow again from their roots or seeds. However, that plant material has not just disappeared: a lot of it has gone up into the sky as smoke. Big wildfires like we have in our African savannas can make so much smoke that it seems as if the smoke is making clouds in the sky. That’s probably why you asked the question about steam and smoke.</p>
<p>Quite a lot of the smoke from a fire is actually steam. All the water in the plant gets evaporated by the heat of the flames, and goes up in the smoke as water vapour. Once the water is gone then the leaves and the stems of the plants burn, and turn into a gas called carbon dioxide. </p>
<p>When fires burn plants they are doing exactly the same thing our bodies do when we eat plants: they are releasing the energy stored in the plant. We eat food and breathe in oxygen. The oxygen joins to the carbon from the food, and makes carbon dioxide that we breathe out. This gives us energy. Fires also need oxygen to “eat” plants. Sometimes when they don’t have enough oxygen they breathe out carbon monoxide or methane instead of carbon dioxide, but all of these gases go up into the air in the smoke. </p>
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Read more:
<a href="https://theconversation.com/curious-kids-what-is-fire-100490">Curious Kids: what is fire?</a>
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<p>However, not every bit of the plant is turned into carbon dioxide in a fire. Some very small particles of ash and soot are not burned, but are taken up into the sky with the water vapour and the carbon dioxide. We call these <a href="https://www.sciencenewsforstudents.org/article/explainer-what-are-aerosols">aerosols</a>: tiny particles that are light enough to stay up in the sky even though they are not a gas. These aerosols are what gives smoke its grey or black colour sometimes. </p>
<p>So, just as water moves around the world as a “<a href="https://gpm.nasa.gov/education/water-cycle">water cycle</a>” – changing from solid to liquid to gas with the help of energy from the sun – carbon also moves around the world in a “carbon cycle”. Fire is part of that cycle, turning solid carbon in plants back into carbon dioxide gas. We breathe out carbon dioxide gas when we eat plants, and fire “breathes out” carbon dioxide gas and other small particles when it burns plants.</p>
<h2>Learning more</h2>
<p>As I said earlier, you can see that not all fires make the same sort of smoke. This is because the amount of aerosols, water vapour, and other gases that come from a fire changes depending on the weather and what sorts of plants are being burned. At the moment I and other scientists are studying fires in Africa at different times of year: we want to see how the smoke from these fires changes over the year. </p>
<p>The way we do this is pretty cool. We fly small helicopters called drones into the smoke and catch packets of the smoke so that we can see what it is made of. There isn’t an actual person flying the drones – that would be dangerous, so the drones are controlled with remotes like you’d use for your TV.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/oUuqiKJfNN4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Scientists flying a drone into a fire so they can study the smoke.</span></figcaption>
</figure>
<p>We take these smoke samples back to the lab and work out how much water vapour, carbon dioxide, and aerosols are in the smoke. This helps us to understand the carbon cycle better, and decide when and how to burn our land so that the smoke doesn’t cause damage to people or the environment.</p><img src="https://counter.theconversation.com/content/172505/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sally Archibald does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Scientists are studying fires in Africa at different times of year to see how the smoke from these fires changes over the year.Sally Archibald, Professor of Ecology, University of the WitwatersrandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1733832021-12-08T13:24:21Z2021-12-08T13:24:21ZSustainable Christmas trees: an ecologist’s buying guide<figure><img src="https://images.theconversation.com/files/436351/original/file-20211208-142574-y5ff6v.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5668%2C3773&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">gpointstudio / shutterstock</span></span></figcaption></figure><p>If you celebrate Christmas, chances are you are planning to decorate a tree (or have already). But how do you make an informed and environment-friendly choice? Environmental impact is a complex question for any product, and as a tree ecologist I know that Christmas trees are no exception.</p>
<p>Lifecycle <a href="https://www.theguardian.com/lifeandstyle/2018/dec/08/are-real-or-fake-christmas-trees-better-for-the-planet">analyses</a>, which look at how much carbon is used in every step of a product’s life, have estimated that plastic trees have a carbon footprint between <a href="https://www.independent.co.uk/life-style/christmas/christmas-tree-real-living-artificial-plastic-environment-carbon-footprint-a9235551.html">ten and 20 times</a> greater than that of a real tree. This isn’t suprising since plastic is derived from fossil fuels, and takes a lot of energy to manufacture. </p>
<p>Real trees, on the other hand, take carbon out of the atmosphere to grow. But once you add in chemical fertilisers, also fossil-fuel hungry, fuel for machinery and transportation, it’s clear that both types of tree will have a solid carbon footprint, albeit lower for a real tree than a plastic one. Unless you invest in a beautiful plastic tree that you or someone else reuse for at least a decade, it might be better to buy a real, grown tree. What should you consider then?</p>
<p>The carbon footprint will grow tremendously with transportation, so a tree grown on the other side of the world isn’t at all a sustainable choice.</p>
<p>Similarly, we have seen that chemical fertilisers have a large carbon footprint. They are also a big source of pollution, potentially affecting rivers, lakes and whole ecosystems. Pesticides are used because Christmas tree farms are monocultures, in which a single species is grown at high density, which puts them at risk of parasitism and diseases. Pesticides are also a problem for the environment, particularly for invertebrates. Growing trees organically can reduce that impact, although this might result in <a href="https://wickedleeks.riverford.co.uk/features/organics-local-sourcing/organic-trees-christmas-myth">“wonky” trees</a> that are less formatted in shape.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/436356/original/file-20211208-68670-1m5g8xo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="small plants in soil" src="https://images.theconversation.com/files/436356/original/file-20211208-68670-1m5g8xo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/436356/original/file-20211208-68670-1m5g8xo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/436356/original/file-20211208-68670-1m5g8xo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/436356/original/file-20211208-68670-1m5g8xo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/436356/original/file-20211208-68670-1m5g8xo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/436356/original/file-20211208-68670-1m5g8xo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/436356/original/file-20211208-68670-1m5g8xo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Six years to go: Christmas tree seedlings.</span>
<span class="attribution"><span class="source">Sharomka / shutterstock</span></span>
</figcaption>
</figure>
<p>The type of land where a tree is grown will also play a big role in its environmental impact. Is a Christmas tree plantation replacing something else, possibly more useful (food, for instance) or better for the environment (old growth forests or <a href="https://theconversation.com/peatlands-keep-a-lot-of-carbon-out-of-earths-atmosphere-but-that-could-end-with-warming-and-development-151364">peatland</a>)? Luckily, in countries where most consumers live, a lot of land that is used to grow Christmas trees used to be low-productivity farmland. </p>
<p>But this doesn’t mean that growing millions of trees every year (<a href="https://www.independent.co.uk/business/retailers-warn-of-potential-christmas-tree-shortage-b1925536.html">8m in the UK</a>, <a href="https://www.cnbc.com/2020/12/03/christmas-tree-sales-are-telling-a-holly-jolly-economic-story.html">20-30m in the US</a>) is the best choice of land allocation. Growing Christmas trees means harvesting them after six to ten years, which means less time for wildlife and bugs to establish thriving populations. Compare them with timber production (cut every 20 to 100 years) or a nature reserve (never) and you will understand why Christmas tree plantations are not considered in the <a href="https://ec.europa.eu/environment/pdf/forests/swd_3bn_trees.pdf">EU tree planting pledge</a>.</p>
<h2>Which species?</h2>
<p>The species of tree might also matter. Christmas tree species are coniferous and include Nordmann fir, Douglas fir, Norway spruce, and more rarely Scots pine. They will likely have different rates of carbon capture, and different interactions with surrounding plants and animals, depending on their physiology and how it matches the soil and climatic environment (I did say it was complicated). </p>
<p>Unfortunately, I am not aware of any study comparing tree species in the context of Christmas tree plantations (monoculture, early harvest). It might be expected that a native tree (like Scots pine in the UK) will be better at hosting local biodiversity, for instance, but that needs testing. Considering the intensive management involved, the differences between species are likely to be small.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/436361/original/file-20211208-159504-119yc7q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Dead christmas tree" src="https://images.theconversation.com/files/436361/original/file-20211208-159504-119yc7q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/436361/original/file-20211208-159504-119yc7q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/436361/original/file-20211208-159504-119yc7q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/436361/original/file-20211208-159504-119yc7q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/436361/original/file-20211208-159504-119yc7q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/436361/original/file-20211208-159504-119yc7q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/436361/original/file-20211208-159504-119yc7q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Now what?</span>
<span class="attribution"><span class="source">PaKo Studio / shutterstock</span></span>
</figcaption>
</figure>
<p>Finally, what should you do when the tree is no longer fit for purpose? Chipping a tree to use as mulch or compost will effectively mean carbon contained in the wood is stored in the soil, which is more stable. Burning the tree releases that carbon into the atmosphere. Dropping it in landfill is the worst as it releases both carbon and methane through slow degradation. The best option is to keep the tree alive so that it grows, captures more carbon, and dies after several decades.</p>
<p>How does all this translate in practice? Here are a few tips:</p>
<p>1) If you like being able to have the same tree that you can store and reuse for years, then a plastic tree might be an option. But check where and how it is produced (sustainability isn’t only about the environment, it is also about people).</p>
<p>2) Buy locally-grown trees, with <a href="https://www.fsc-uk.org/en-uk/about-fsc/what-is-fsc/frequently-asked-questions">Forest Stewardship Council certification</a>. If possible, check for additional characteristics such as whether it’s organically grown, native and not grown on peatland. And don’t have it wrapped in a plastic net.</p>
<p>3) Ask your council about recycling options. If you can do it yourself, chip the wood and use as mulch, or use the branches to build nests for <a href="https://theconversation.com/uk/topics/native-bees-82539">native bees</a>.</p>
<p>4) Consider buying pot-grown trees, which you can keep for several years. But note that this is different from potted trees, which are grown in the soil and then dug up – the root system of potted trees won’t really support them. </p>
<p>5) If you are not too attached to the traditional look of a tree, why not consider timber-made <a href="https://www.etsy.com/uk/market/wooden_christmas_tree">alternatives</a> that you buy or make yourself, or even just decorate your house plants? After all, in a world of overconsumption, the most sustainable option is to avoid getting a new tree at all.</p>
<hr>
<figure class="align-right ">
<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
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<p><strong><em>Don’t have time to read about climate change as much as you’d like?</em></strong>
<br><em><a href="https://theconversation.com/uk/newsletters/imagine-57?utm_source=TCUK&utm_medium=linkback&utm_campaign=Imagine&utm_content=DontHaveTimeTop">Get a weekly roundup in your inbox instead.</a> Every Wednesday, The Conversation’s environment editor writes Imagine, a short email that goes a little deeper into just one climate issue. <a href="https://theconversation.com/uk/newsletters/imagine-57?utm_source=TCUK&utm_medium=linkback&utm_campaign=Imagine&utm_content=DontHaveTimeBottom">Join the 10,000+ readers who’ve subscribed so far.</a></em></p>
<hr><img src="https://counter.theconversation.com/content/173383/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul Caplat received funding from the Swedish Resarch Council "FORMAS" to study bird and butterfly biodiversity in managed forests.</span></em></p>Here’s what to look out for.Paul Caplat, Senior Lecturer in Global Change Ecology, Queen's University BelfastLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1716572021-11-16T20:34:44Z2021-11-16T20:34:44ZVery hungry caterpillars can have large effects on lake quality and carbon emissions<figure><img src="https://images.theconversation.com/files/432041/original/file-20211115-17-zxtklw.JPG?ixlib=rb-1.1.0&rect=47%2C35%2C3898%2C2173&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">These insects are basically little machines that convert carbon-rich leaves into nitrogen-rich poo.</span> <span class="attribution"><span class="source">(John Gunn)</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Outbreaks of invasive moth caterpillars, <em>Lymantria dispar dispar</em>, and forest tent caterpillar moths, <em>Malacasoma disstria</em>, occur at least every five years in temperate forests. The insects munch through so many leaves that <a href="https://doi.org/10.1038/s41467-021-26666-1">our research has found</a> the resulting decrease in leaf-fall and increase in caterpillar poop hugely alter the way nutrients, particularly carbon and nitrogen, cycle between land and nearby lakes.</p>
<p>Nitrogen-rich insect excrement, called frass, can wash into lake water and act as fertilizer for microbes. These microbes can then release carbon dioxide into the atmosphere as they metabolize the frass. In years with insect outbreaks, the large quantities of frass may favour the growth of bacteria that release greenhouse gases in lakes <a href="https://doi.org/10.4319/lo.1984.29.2.0298">overpowering the lake algae that remove carbon dioxide from the atmosphere</a>.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-an-invasive-caterpillar-is-munching-its-way-through-tree-leaves-in-the-largest-outbreak-in-decades-163346">Why an invasive caterpillar is munching its way through tree leaves, in the largest outbreak in decades</a>
</strong>
</em>
</p>
<hr>
<figure class="align-right ">
<img alt="Caterpillars on a chewed green leaf." src="https://images.theconversation.com/files/432074/original/file-20211115-13-1j2he1b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/432074/original/file-20211115-13-1j2he1b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=412&fit=crop&dpr=1 600w, https://images.theconversation.com/files/432074/original/file-20211115-13-1j2he1b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=412&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/432074/original/file-20211115-13-1j2he1b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=412&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/432074/original/file-20211115-13-1j2he1b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=518&fit=crop&dpr=1 754w, https://images.theconversation.com/files/432074/original/file-20211115-13-1j2he1b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=518&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/432074/original/file-20211115-13-1j2he1b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=518&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Tree leaves eaten by caterpillars on Montreal’s Mount Royal in July 2021.</span>
<span class="attribution"><span class="source">THE CANADIAN PRESS/Paul Chiasson</span></span>
</figcaption>
</figure>
<p>These insects are basically little machines that convert carbon-rich leaves into nitrogen-rich poo. The poo drops into lakes instead of the leaves, and this significantly changes the water chemistry. We think it will further increase the extent to which lakes are sources of greenhouse gases. </p>
<p>As the climate in the world’s temperate region shifts, insect populations are expected to increase and move northwards. This puts <a href="https://doi.org/10.1046/j.1365-2486.2002.00451.x">northern forests at increased risk of defoliator outbreaks in the future</a>, potentially causing greater quantities of carbon dioxide to be released from nearby lakes. Climate change is also expected to favour the growth of broad-leaved deciduous trees around the lakes, which we have found will amplify the insects’s impact.</p>
<h2>Where is the good news?</h2>
<p>While the impacts of insect defoliation appear to be on the rise in both frequency and severity, lake waters across the Canadian Shield are also undergoing a <a href="https://doi.org/10.1038/444283a">process called browning</a> due to a build up of tea-like dissolved organic carbon in lake water. </p>
<p>This declining clarity of lakes has been attributed to many factors including climate change and their recovery from historical acid rain and logging activities. Our 32-year-long monitoring study showed that an outbreak of leaf-munching caterpillars can effectively offset an entire year’s worth of carbon accumulation in nearby lakes, significantly improving water clarity.</p>
<figure class="align-center ">
<img alt="A view of autumn trees along a lake shoreline" src="https://images.theconversation.com/files/432078/original/file-20211115-13-hlgdt0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/432078/original/file-20211115-13-hlgdt0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/432078/original/file-20211115-13-hlgdt0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/432078/original/file-20211115-13-hlgdt0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/432078/original/file-20211115-13-hlgdt0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/432078/original/file-20211115-13-hlgdt0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/432078/original/file-20211115-13-hlgdt0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An outbreak of leaf-munching caterpillars can effectively offset an entire year’s worth of carbon accumulation in nearby lakes, significantly improving water clarity.</span>
<span class="attribution"><span class="source">(Unsplash)</span></span>
</figcaption>
</figure>
<p>In years without outbreaks of leaf-eating insects, carbon and nitrogen entering lakes usually comes from decaying leaves and conifer needles. These inputs typically peak in quantity in autumn. In outbreak years, we found that nearby freshwater lakes, especially those surrounded by deciduous forests had one-third less dissolved carbon or “forest tea” in the water, because the hungry caterpillars effectively held back the flow of carbon to the lake.</p>
<p>The lasting benefits of these marauding insects becomes evident when the invasive insects encounter already stressed trees, such as the stunted birch forest surrounding the massive metal smelters in Sudbury, Ont. This 80,000 hectare industrial area is undergoing a remarkable natural recovery of its own, because of a <a href="https://theconversation.com/what-mining-oil-and-gas-industries-can-learn-from-sudbury-the-city-that-went-from-major-polluter-to-thriving-environment-165595">98 per cent reduction in acid and metal particulate emissions</a> from what was <a href="https://www.goodnewsnetwork.org/sudbury-now-has-cleanest-air-in-region/">the world’s largest point sources of sulphur pollution as recently as the 1970s</a>. The legacy of soil loss, contamination and degradation in Sudbury clearly puts trees at a disadvantage in the battle with defoliating insects.</p>
<h2>Caterpillars as tiny plows?</h2>
<p>Trees can’t flee from insects but usually can survive multiple heavy attacks. However, trees in the industrial barrens of Sudbury don’t fare so well, because of all the other stresses they face. </p>
<p>These stressors include the loss of soil moisture and organic matter, and decades of accumulated toxic metal particles from the smelters. The result is that these stressed trees present themselves as a delicious food source for caterpillars and other insects and the landscape is often littered with dead and dying trees on their way to becoming soil.</p>
<p><a href="https://doi.org/10.1093/ee/nvz096">In earlier lab experiments</a>, we showed that when we fed <em>L. dispar</em> caterpillars leaves from the stressed white birch trees of the industrial barrens they ate more leaves and produced far more frass, which increased plant growth in soil that had received this rain of poo. </p>
<p>Yes, the insects are giving the struggling trees a very hard time at the industrial sites. But the improving soil quality is the real winner. </p>
<p>Healthy <a href="https://e360.yale.edu/features/soil_as_carbon_storehouse_new_weapon_in_climate_fight">soil is one of the largest and safest places to sequester carbon from the atmosphere</a>, key in our fight against climate change. As every farmer knows, protecting and restoring soil quality is also essential for sustainable agriculture. That is why well-informed farmers regularly try to stop extracting nutrients from the soil and plow in a nutrient-rich fodder crop like alfalfa to rebuild the soil.</p>
<p>Our research shows that these hungry caterpillars now appear to play surprisingly large roles in altering key features of the global carbon cycle, but we also now think of them as tiny plows that can help improve degraded soils.</p><img src="https://counter.theconversation.com/content/171657/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Gunn receives funding from organisation.
NSERC, CRC, CFI, Mitacs, OCE, Vale, Glencore, Wildlife Conservation Society, DFO, Friends of Killarney</span></em></p><p class="fine-print"><em><span>Andrew J Tanentzap receives funding from the Natural Environment Research Council, Biotechnology and Biological Sciences Research Council, and European Research Council.</span></em></p><p class="fine-print"><em><span>Samuel Woodman receives funding from NSERC and the Cambridge Trust. </span></em></p>As environmental engineers, invasive caterpillars can have remarkable effects on water quality and soil conditions. But from a climate perspective they’re pretty much a nuisance.John Gunn, Canada Research Chair in Stressed Aquatic Systems, Laurentian UniversityAndrew J Tanentzap, Reader in Global Change Ecology, University of CambridgeSamuel Woodman, PhD Student, Ecosystem and Global Change, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1709852021-11-03T16:44:45Z2021-11-03T16:44:45ZWhy the fate of our planet’s environment depends on the state of its soil<figure><img src="https://images.theconversation.com/files/429947/original/file-20211103-13-1x2dcvw.jpeg?ixlib=rb-1.1.0&rect=0%2C0%2C1276%2C848&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Many of our planet's ecosystems depend on the health of soil.</span> <span class="attribution"><a class="source" href="https://pixabay.com/photos/greenhouse-planting-spring-beds-6226263/">Katya_Ershova/Pixabay</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>In 1937, Franklin Roosevelt, then president of the US, wrote to state governors in the wake of the “<a href="https://www.history.com/topics/great-depression/dust-bowl">dust bowl</a>” catastrophe, where drought across the <a href="https://www.drought.gov/dews/southern-plains">Southern Plains</a> led to catastrophic famine and dust storms. “The nation that destroys its soils destroys itself,” he wrote, highlighting what remains a fundamental truth: that the state of the Earth’s soil is a vital indicator of the planet’s health.</p>
<p>As a society, we do not place <a href="https://www.pnas.org/content/113/22/6105">sufficient value</a> on the ground beneath our feet. The use of the word “dirt” to denote inferiority is an example of this disrespect for our land. Yet societies succeed and fail as a direct <a href="https://digitalcommons.pepperdine.edu/cgi/viewcontent.cgi?article=1019&context=globaltides">consequence</a> of the value they place on their soils.</p>
<p>Our soil not only directly or indirectly provides most of our food, but it’s also central to our planet’s life-support system. Soil is an integral component of the <a href="https://theconversation.com/carbon-catch-22-the-pollution-in-our-soil-78718">carbon</a>, water and nutrient cycles, which allow organisms of all sizes to to thrive.</p>
<p>When plants and animals decompose, their bodies release nutrients into the soil for subsequent generations of organisms to use and recycle. Soils store, filter and purify our water, helping to protect against <a href="https://www.eea.europa.eu/highlights/forests-can-help-prevent-floods">flash flooding</a> through absorbing rainwater. And soils are critical for <a href="https://news.climate.columbia.edu/2018/02/21/can-soil-help-combat-climate-change/">carbon storage</a>, helping buffer our climate against the effects of human-driven carbon emissions. There is an estimated <a href="https://www.annualreviews.org/doi/abs/10.1146/annurev.earth.35.031306.140057">three times</a> more carbon in our soils than in Earth’s atmosphere.</p>
<p>But these ecosystem services are fragile and can easily break down. By mistreating soil through <a href="https://ec.europa.eu/environment/integration/research/newsalert/pdf/14si5_en.pdf">deep ploughing</a> (which damages soil structure) and using <a href="https://www.fao.org/3/a0100e/a0100e0d.htm">harsh chemicals</a> (which kill important microbe communities), many of our soils are now degraded. It’s estimated that <a href="https://www.theguardian.com/environment/2015/dec/02/arable-land-soil-food-security-shortage#:%7E:text=5%20years%20old-,Earth%20has%20lost%20a%20third%20of%20arable,past%2040%20years%2C%20scientists%20say&text=The%20world%20has%20lost%20a,food%20soars%2C%20scientists%20have%20warned.">one-third</a> of our agricultural soils have been lost over the past 40 years.</p>
<p>This reduces our ability to produce high-quality food. Soils in poor condition can require more fertiliser, since they cannot trap nitrogen and phosphorus. Manufacturing nitrogen fertiliser to make up for this is a significant source of carbon emissions: nearly <a href="https://www.nature.com/articles/nplants201712">600g of CO₂</a> is produced in making an 800g loaf of bread, with 43% of these emissions arising from nitrogen fertiliser alone.</p>
<figure class="align-center ">
<img alt="A tractor ploughs a field" src="https://images.theconversation.com/files/430011/original/file-20211103-13-o0ft6e.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/430011/original/file-20211103-13-o0ft6e.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=606&fit=crop&dpr=1 600w, https://images.theconversation.com/files/430011/original/file-20211103-13-o0ft6e.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=606&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/430011/original/file-20211103-13-o0ft6e.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=606&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/430011/original/file-20211103-13-o0ft6e.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=761&fit=crop&dpr=1 754w, https://images.theconversation.com/files/430011/original/file-20211103-13-o0ft6e.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=761&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/430011/original/file-20211103-13-o0ft6e.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=761&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Deep ploughing disturbs the natural composition of soil and the organisms that inhabit it, leaving it vulnerable to erosion.</span>
<span class="attribution"><a class="source" href="https://pixabay.com/photos/gerridae-guerrido-aquatic-insect-1415382/">MemoryCatcher/Pixabay</a></span>
</figcaption>
</figure>
<p>On top of this, degradation can also lead to soils releasing their stored carbon as CO₂, amplifying the climate crisis. In 2015, when I spoke at the UN climate change conference <a href="https://www.fao.org/global-soil-partnership/resources/events/detail/en/c/330852/">COP21</a> in Paris, I warned of impending disaster if we don’t protect our soils from degradation with techniques which reduce soil erosion, such as planting cover crops. </p>
<p>At that time, I was <a href="https://digitalmedia.sheffield.ac.uk/media/Bright+Minds++-+Food+Sustainability/1_wei1otk8/199532763">described</a> as a “peddler of university disaster pornography” by climate change deniers. But my testimony was not some fanciful prediction. As studying the dust bowl reminds us, the <a href="https://www.pbs.org/kenburns/the-dust-bowl/legacy">repercussions</a> of soil degradation are still being felt today. </p>
<h2>Degradation</h2>
<p>Across the UK, soils have been degraded due to intensive agriculture, leaving them vulnerable to erosion by extreme weather. In the spring of 2014, when heavy rainfall across the UK saturated land, degraded soils were unable to store water, leading to <a href="https://www.theguardian.com/environment/2014/feb/11/englands-floods-everything-you-need-to-know">widespread flooding</a> and soil erosion. That month, the Earth observation centre <a href="https://www.neodaas.ac.uk/">NEODAAS</a> in Plymouth released a satellite image of the UK “<a href="https://ntplanning.wordpress.com/2018/06/13/taking-the-initiative-to-deliver-soil-health-for-uk-agricultural-soils/">bleeding</a>” its soils into the ocean. </p>
<p>We understand why this happens. Ploughing breaks down conglomerations of inorganic soil particles such as clay and sand, bound together by <a href="https://www.sare.org/publications/building-soils-for-better-crops/what-is-organic-matter-and-why-is-it-so-important/">organic material</a> such as dead roots, fungal filaments and bacterial and earthworm secretions. These store organic carbon and build soil structure. Without them, soils wash out more easily into our rivers and estuaries. </p>
<figure class="align-center ">
<img alt="An earthworm on moss" src="https://images.theconversation.com/files/429950/original/file-20211103-18-1s1naob.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429950/original/file-20211103-18-1s1naob.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429950/original/file-20211103-18-1s1naob.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429950/original/file-20211103-18-1s1naob.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429950/original/file-20211103-18-1s1naob.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429950/original/file-20211103-18-1s1naob.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429950/original/file-20211103-18-1s1naob.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Organisms such as earthworms contribute to soil health, but are negatively affected by fertilisers and ploughing.</span>
<span class="attribution"><a class="source" href="https://pixabay.com/photos/earthworms-the-frog-s-perspective-2773457/">Catarina132/Pixabay</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Recent research at the universities of Sheffield, York and Leeds has shown how we might fix this problem: by using no or shallow ploughing, rotating land used for farming, and planting cover crops, all of which allow our soils to <a href="https://eprints.whiterose.ac.uk/172056/">rest and recover</a>. Coupled with limiting fertilisers, this allows populations of beneficial soil organisms like earthworms, fungi and bacteria to increase. </p>
<h2>Regeneration</h2>
<p>This evidence supports growing calls to embrace <a href="https://www.climaterealityproject.org/blog/what-regenerative-agriculture">regenerative agriculture</a>, which calls for supporting – rather than fighting – biodiversity within the agricultural landscape. </p>
<p>In South America, for example, the popular method of “slash, burn and move on” agriculture – where forests are felled, burned to release nutrients and then farmed until those nutrients are depleted – has been criticised for its destruction of biodiversity. In contrast, regenerative agriculture’s focus on increasing biodiversity has been shown to be a <a href="https://www.nature.org/en-us/about-us/where-we-work/latin-america/stories-in-latin-america/transforming-agriculture-to-unleash-the-regenerative-power-of-na/">success</a> in terms of protecting and even increasing soil health in the region. </p>
<figure class="align-center ">
<img alt="Plants grow in an urban greenhouse" src="https://images.theconversation.com/files/429951/original/file-20211103-27-1mq8oto.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429951/original/file-20211103-27-1mq8oto.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429951/original/file-20211103-27-1mq8oto.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429951/original/file-20211103-27-1mq8oto.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429951/original/file-20211103-27-1mq8oto.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=564&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429951/original/file-20211103-27-1mq8oto.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=564&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429951/original/file-20211103-27-1mq8oto.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=564&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Growing food in urban spaces could help protect our planet’s remaining arable land and feed rising populations.</span>
<span class="attribution"><a class="source" href="https://pixabay.com/photos/greenhouse-agriculture-farm-3247181/">WiselyWoven/Pixabay</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Part of regenerative agriculture involves taking pressure off our soils, which might appear tricky in light of the need to feed a growing global population. <a href="https://www.sheffield.ac.uk/sustainable-food">Our research</a> has shown that producing more food in the <a href="https://www.sciencedaily.com/releases/2020/03/200317130713.htm">urban environment</a> could help achieve this.</p>
<p>Crops can be grown in <a href="https://www.telegraph.co.uk/news/2020/03/19/cities-should-grow-fruit-vegetables-roadside-verges-study-claims/">crowded cities</a> using highly efficient hydroponic systems, which use less water, less fertiliser and require no soil. These can operate on top of flat-roofed buildings – or even in <a href="https://www.youtube.com/watch?v=5TP65QA3Vhc&ab_channel=WorldFoodForum">refugee camps</a>, where farming enhances food security and community resilience. By growing crops close to where people live, we can remove the need to ship food around the globe, making our food systems much more sustainable.</p>
<p><a href="https://www.fao.org/3/cb3808en/cb3808en.pdf">Almost 20%</a> of greenhouse gas emissions currently arise from agriculture: meaning that carbon is effectively leaking out of our soils across the world. That means we urgently need to embrace technologies that take a soil-centric view of food production if we are to leave a functional agricultural ecosystem for future generations.</p><img src="https://counter.theconversation.com/content/170985/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Duncan Cameron receives funding from BBSRC, NERC and the Royal Society.</span></em></p>If we want to reduce carbon emissions and preserve planetary ecosystems, we need to protect our soils.Duncan Cameron, Professor of Plant and Soil Biology, University of SheffieldLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1607402021-05-27T09:28:01Z2021-05-27T09:28:01ZWhat would happen to the climate if we reforested the entire tropics?<figure><img src="https://images.theconversation.com/files/401981/original/file-20210520-13-tca2nq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">pio3/shutterstock</span></span></figcaption></figure><p>What would happen if every single patch of farmland in the tropics, from Brazil through Congo, India and Indonesia, was abandoned overnight and left to turn back into forests? That’s the question we investigated in our <a href="https://bg.copernicus.org/articles/18/2627/2021/">new research</a>. Trees and forests have become increasingly important in plans to tackle the climate emergency, yet our work shows that once you factor in how the soil, oceans and other parts of the Earth system would respond, tree planting is not as potent a solution as it may first seem.</p>
<p>Of course, abandoning agriculture in the tropics cannot be a solution to climate change. This was a hypothetical and idealised experiment, but one that helps us to explore how the global carbon cycle might respond to forest restoration and tree planting on a vast scale. And targeting the tropics shows maximum impact as trees grow fast there.</p>
<p>To investigate the question, we used the UK Met Office’s climate change model – a computer simulation of the Earth as a system in which the oceans, land and climate interact and affect each other. We simulated two futures. First, a scenario where the world takes serious action to limit warming to less than 2°C. The second scenario was identical, except all farming across the tropics was stopped and the original vegetation, mostly forests, would recover. </p>
<p>The difference between the two scenarios shows that the new tropical trees would store an extra 124 billion tonnes of carbon by the year 2100, or around 13 years’ worth of <a href="https://www.globalcarbonproject.org/carbonbudget/index.htm">today’s rate of fossil fuel emissions</a>. All this extra carbon would have been taken from the atmosphere through photosynthesis. However, carbon in the atmosphere – which matters for climate change – would drop by only 18 billion tonnes, just two years’ worth of emissions. What explains the huge difference? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/402950/original/file-20210526-21-bnipcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Large tree root in tropical forest" src="https://images.theconversation.com/files/402950/original/file-20210526-21-bnipcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/402950/original/file-20210526-21-bnipcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402950/original/file-20210526-21-bnipcy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402950/original/file-20210526-21-bnipcy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402950/original/file-20210526-21-bnipcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402950/original/file-20210526-21-bnipcy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402950/original/file-20210526-21-bnipcy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Reforesting the tropics would mean more carbon stored in trees, but less absorbed in soil.</span>
<span class="attribution"><span class="source">Serge Goujon/shutterstock</span></span>
</figcaption>
</figure>
<p>The reason is that other parts of the Earth system counteract the effect of the new tree growth. If the tropics were reforested, our model predicts that the oceans, soil and vegetation would absorb less carbon dioxide. By the end of the century, tropical trees would take up an extra 124 billion tonnes of carbon (or 124 gigatonnes, Gt), but tropical soils would take up 83 Gt less carbon, as the turnover of dead plants is much slower in forests compared with grasses and crops that die annually, meaning lower carbon inputs in forest soils and lower carbon storage. </p>
<p>Lower carbon dioxide levels in the atmosphere would also affect vegetation and soils elsewhere in the world. Less carbon dioxide in the atmosphere would mean plant growth slows. And just as in the tropics, less carbon would be taken up by soils. </p>
<p>There would be one other major change to the Earth system. The oceans slow climate change by removing carbon dioxide from the atmosphere: as CO₂ levels increase some of the extra carbon dioxide dissolves into the seawater. And in our model, the oceans would take up less carbon since the new tropical trees would lower atmospheric CO₂.</p>
<p>To recap: we started with new trees in the tropics taking 124 Gt of carbon out of the atmosphere. Avoiding deforestation adds a further 10 Gt. But once you subtract the carbon no longer stored in tropical forest soils (83 Gt), in soils and vegetation elsewhere (18 Gt), and in the oceans (15 Gt), you aren’t left with much. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/402937/original/file-20210526-17-11xxg4p.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Chart showing flows of carbon in and out of the atmosphere." src="https://images.theconversation.com/files/402937/original/file-20210526-17-11xxg4p.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/402937/original/file-20210526-17-11xxg4p.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402937/original/file-20210526-17-11xxg4p.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402937/original/file-20210526-17-11xxg4p.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402937/original/file-20210526-17-11xxg4p.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402937/original/file-20210526-17-11xxg4p.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402937/original/file-20210526-17-11xxg4p.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">How the full tropical reforestation scenario adds up.</span>
<span class="attribution"><span class="source">Lewis, Koch, Brierley</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Remarkably, reforesting the tropics – after accounting for soil, vegetation, and ocean responses – results in only 18 Gt of carbon taken from the atmosphere. This is an 86% reduction from our initial extra carbon in tropical trees. This 18 Gt equates to just ten parts per million reduction in atmospheric carbon dioxide.</p>
<h2>The Earth system works against us</h2>
<p>What we found in our hypothetical scenario is the reverse of what is happening today. When carbon dioxide is released from burning fossil fuels, a little less than half of those emissions remain in the atmosphere and contribute to climate change. The rest are absorbed by the oceans, soil and vegetation. This has been a great free subsidy from nature. </p>
<p>But here is the catch: just as the amount of carbon absorbed in the land and ocean increases as we pump more carbon dioxide into the atmosphere, the reverse happens when we take it out of the atmosphere. The Earth system starts to work against us when we plant trees or use other methods of removing atmospheric CO₂.</p>
<p>These results are sobering. Even something as radical as reforesting the entire tropics – far beyond any plausible real-world policy outcome – would have less influence on the climate than you might think. But these results also highlight that the best way to avoid dangerous global heating is by not releasing fossil carbon into the atmosphere in the first place.</p><img src="https://counter.theconversation.com/content/160740/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Simon Lewis has received funding from Natural Environment Research Council, the Royal Society, the European Union, the Leverhulme Trust, the Centre for International Forestry, National Parks Agency of Gabon, Microsoft Research, the Gordon and Betty Moore Foundation, the Greenpeace Fund, the David and Lucile Packard Foundation and the Children's Investment Fund. </span></em></p><p class="fine-print"><em><span>Chris Brierley receives funding from the Natural Environment Research Council and the UK Met Office. </span></em></p><p class="fine-print"><em><span>Alexander Koch does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Even this radical scenario wouldn’t be as effective as it may first seem.Simon Lewis, Professor of Global Change Science at University of Leeds and, UCLAlexander Koch, Postdoctoral Research Associate, Earth Sciences, University of Hong KongChris Brierley, Associate Professor of Geography, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1547302021-02-28T13:36:43Z2021-02-28T13:36:43ZPlastic is part of the carbon cycle and needs to be included in climate calculations<figure><img src="https://images.theconversation.com/files/386575/original/file-20210225-21-1r6l49w.jpg?ixlib=rb-1.1.0&rect=17%2C8%2C5973%2C2982&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The plastic problem isn't separate from climate change.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>Plastic pollution and climate change are two prominent environmental issues of our time. Plastic was once thought to be a miracle invention that made <a href="https://thedieline.com/blog/2020/3/10/the-history-of-plastic-the-invention-of-throwaway-living">life simpler</a> for families. </p>
<p>But just as our exploitation of fossil fuels led to climate change, the unsustainable use of plastic materials has led to a global environmental catastrophe. To this day, plastic pollution has infiltrated every part of our planet, from <a href="https://doi.org/10.1016/j.marpolbul.2014.06.001">remote mountain lakes</a> to <a href="https://doi.org/10.1098/rsos.180667">the ocean</a> to the <a href="https://doi.org/10.1021/acs.est.9b03427">very air we breathe</a>. </p>
<p>The unsustainable consumption of nonrenewable resources is the common root of both these problems, and beneath the surface, there are many links between these two issues.</p>
<h2>Plastic is part of the carbon cycle</h2>
<p>To better understand <a href="https://doi.org/10.3389/fmars.2020.609243">how plastic particles move through the environment</a>, scientists should <a href="https://doi.org/10.1038/s41561-018-0077-9">investigate their transport</a> as they do for <a href="https://science.sciencemag.org/content/368/6496/1184">nitrogen, carbon and water</a>.</p>
<p>To do this, they should formally adopt the terminology used to study these biogeochemical cycles, including “reservoirs,” which are places of storage, and “fluxes,” which describe the movement of substances from one place to another over time. This will help us understand the transport mechanisms and fate of plastic pollution in the environment, which are major gaps in the field today. </p>
<figure class="align-center ">
<img alt="Plastic bottles floating in an ocean harbour." src="https://images.theconversation.com/files/386576/original/file-20210225-13-1pt52tn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/386576/original/file-20210225-13-1pt52tn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/386576/original/file-20210225-13-1pt52tn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/386576/original/file-20210225-13-1pt52tn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/386576/original/file-20210225-13-1pt52tn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/386576/original/file-20210225-13-1pt52tn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/386576/original/file-20210225-13-1pt52tn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Plastic should be studied in the same way nitrogen, carbon and water are, so that scientists can understand its movement and its fate.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<p>In fact, all the plastic that has ever been produced is part of the carbon cycle. Overall, an enormous <a href="https://www.doi.org/10.1126/sciadv.1700782">seven gigatonnes</a> — or seven billion tonnes — of plastic have been produced, mainly from chemicals extracted from the <a href="https://earthobservatory.nasa.gov/features/CarbonCycle">fossil carbon reservoir</a>. This is not much different from the roughly <a href="https://ourworldindata.org/greenhouse-gas-emissions">14 billion tonnes of carbon</a> emitted into the atmosphere every year from the same reservoir due to human activities.</p>
<p>Plastic transports carbon in different ways. For instance, plastic can become <a href="https://doi.org/10.1038/s41598-019-55990-2">incorporated into living organisms</a>, or settle to the bottom of the ocean as aggregates of plastic and organic matter. It can also <a href="https://www.ciel.org/plasticandclimate/">release greenhouse gases</a> at every stage of its life cycle, from production to transportation to waste disposal. Scientists and governments should investigate how plastic pollution transports carbon because nutrient redistribution has implications for the livelihoods of ecosystems and the well-being of living organisms. </p>
<p>Since plastic polymers are so persistent, almost every piece of plastic we have ever produced is still somewhere on this planet. This suggests, due to the sheer amount of plastic pollution, that plastic pollution is on the same scale as global transport processes of carbon, also on the order of gigatonnes. </p>
<p>The key takeaway is that plastic pollution <a href="https://www.frontiersin.org/articles/10.3389/fmars.2020.609243/full">has its own cycle</a>, and that it may also play a fundamental role in the carbon cycle — the movement of carbon between different reservoirs such as the atmosphere, ocean and organisms — a cycle that is very relevant to global climate change. </p>
<h2>Two sides of the same coin</h2>
<p>Several recent <a href="https://www.wired.co.uk/article/climate-change-plastic-pollution">articles by journalists</a> and <a href="https://theconversation.com/climate-change-obsession-with-plastic-pollution-distracts-attention-from-bigger-environmental-challenges-111667">scientists</a> have framed the plastic pollution problem as a <a href="https://www.sciencedaily.com/releases/2020/10/201023123128.htm">distraction from the problem of climate change</a>. The issue of plastic pollution may compete with climate change for funding and attention, delaying action what is a more pressing environmental issue, they say. </p>
<p>I disagree. Research shows that the plastic problem is <a href="https://www.ciel.org/issue/fossil-fuels-plastic/">not independent</a> from climate change. </p>
<figure class="align-center ">
<img alt="Plumes billow from two industrial stacks." src="https://images.theconversation.com/files/384061/original/file-20210212-19-16eof9e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/384061/original/file-20210212-19-16eof9e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/384061/original/file-20210212-19-16eof9e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/384061/original/file-20210212-19-16eof9e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/384061/original/file-20210212-19-16eof9e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/384061/original/file-20210212-19-16eof9e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/384061/original/file-20210212-19-16eof9e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Greenhouse gas emissions from the burning of fossil fuels.</span>
<span class="attribution"><span class="source">(Pixabay)</span></span>
</figcaption>
</figure>
<p>Plastic and climate are two sides of the same coin: the <a href="https://www.ellenmacarthurfoundation.org/publications/the-new-plastics-economy-rethinking-the-future-of-plastics">majority of plastic polymers</a> are made from petrochemical feed-stocks and their raw materials for synthesis are ethylene and propylene. These compounds are derived from <a href="https://www.polyplastics.com/en/pavilion/beginners/01-05.html">naphtha, one of several chemicals refined from petroleum</a>. What else is refined from petroleum? <a href="https://www.nationalgeographic.org/encyclopedia/petroleum/">Gasoline</a>, the fossil fuel we burn for energy that emits greenhouse gases. </p>
<p>These sister compounds are used differently but they have a common origin and they instigate the very issues in question. When demand for petroleum drops, companies <a href="https://e360.yale.edu/features/the-plastics-pipeline-a-surge-of-new-production-is-on-the-way">ramp up</a> their plastic production. When demand for plastic drops, fossil fuel companies might be inclined to shift their production ratio again. Failing to recognize the intimate connections between these issues not only makes tackling these issues inefficient, but may also undermine efforts on both fronts. </p>
<h2>Moving forward</h2>
<p>Through the many years of efforts by researchers, activists, and policy-makers around the world, we are starting to see a big difference in public attitude towards these issues. On the climate front, the adoption of the <a href="https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement">Paris Agreement</a> and the energy of the <a href="https://fridaysforfuture.org/">youth movement</a> fill me with optimism. </p>
<figure class="align-center ">
<img alt="A display of world nations at the COP21 meeting in Paris." src="https://images.theconversation.com/files/384063/original/file-20210212-21-q5fiwh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/384063/original/file-20210212-21-q5fiwh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/384063/original/file-20210212-21-q5fiwh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/384063/original/file-20210212-21-q5fiwh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/384063/original/file-20210212-21-q5fiwh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/384063/original/file-20210212-21-q5fiwh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/384063/original/file-20210212-21-q5fiwh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Paris Climate Summit (COP21) in 2015.</span>
<span class="attribution"><span class="source">(COP21 UofT Students, 2015)</span></span>
</figcaption>
</figure>
<p>On the plastic pollution front, a <a href="https://tos.org/oceanography/article/the-story-of-plastic-pollution-from-the-distant-ocean-gyres-to-the-global-policy-stage">UN international agreement</a> to limit emissions of plastic may be on the horizon. </p>
<p>By acknowledging the connections between these issues, I only see benefits. Climate plans should acknowledge the greenhouse gas emissions from plastics and how plastics can be better managed. For instance, Canada’s <a href="https://www.canada.ca/en/services/environment/weather/climatechange/climate-plan/climate-plan-overview.html">most recent climate plan</a> acknowledged its ban on single-use items in 2021 and recognized the importance of transitioning to a <a href="https://www.ellenmacarthurfoundation.org/our-work/activities/new-plastics-economy">circular economy</a>. Likewise, plastic pollution plans can describe the benefits to that city, state or country’s climate strategy by mitigating plastic production. </p>
<p>Moving forward, we should keep this in mind and tackle these two issues together — the opportunities to do so are plentiful.</p><img src="https://counter.theconversation.com/content/154730/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Xia Zhu received funding from the Vanier Canada Graduate Scholarship. She is affiliated with the People's Climate Movement.</span></em></p>Plastic has become a major part of the carbon cycle, a discovery that has implications for how we tackle climate change.Xia Zhu, PhD Student, Ecology and Evolutionary Biology, University of TorontoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1391822021-01-11T15:43:00Z2021-01-11T15:43:00ZPeat bogs: restoring them could slow climate change – and revive a forgotten world<figure><img src="https://images.theconversation.com/files/378044/original/file-20210111-19-rl935r.jpg?ixlib=rb-1.1.0&rect=0%2C385%2C5360%2C3185&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/scottish-shieling-hut-on-peat-bog-1811122417">Helen Hotson/Shutterstock</a></span></figcaption></figure><p>Bogs, mires, fens and marshes – just their names seem to conjure myth and mystery. Though today, our interest in these waterlogged landscapes tends to be more prosaic. Because of a lack of oxygen, they can build up vast quantities of organic matter that <a href="https://www.britannica.com/technology/peat">doesn’t decompose properly</a>. This is known as peat. Peatlands could contain as much as <a href="https://www.nature.com/articles/s41467-018-03406-6">644 gigatons of carbon</a> – one-fifth of all the carbon stored in soil on Earth. Not bad for a habitat that stakes a claim to <a href="https://www.iucn.org/resources/issues-briefs/peatlands-and-climate-change">just 3%</a> of the planet’s land surface.</p>
<p>Peatlands were once widespread throughout the UK, but many have been dug up, drained, burned, built on and converted to cropland, so their place in history <a href="http://richardlindsayartsandletters.org.uk/peatlands-are-as-important-as-forests-to-the-global-ecosystem-world-conservation-congress">has been forgotten</a>. But while most of the debate around using natural habitats to draw down carbon from the atmosphere concerns planting trees and reforestation, some ecologists argue that <a href="https://www.bbc.co.uk/news/uk-49074872#:%7E:text=Restoring%20peat%20moors%20degraded%20by,have%20been%20drained%20for%20farming.">a far better solution</a> lies in restoring the peatlands that people have spent centuries draining and destroying.</p>
<p>With the government now <a href="https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/936567/10_POINT_PLAN_BOOKLET.pdf">proposing</a> to do this across the UK, it’s worth unearthing the hidden heritage of these landscapes, and how they once fuelled daily life.</p>
<h2>The bare necessities</h2>
<p>The peat bogs that you find in temperate countries like the UK can be centuries or even thousands of years old. Over the course of their long history, peatlands have provided the necessities of life for communities nearby. In medieval Britain, people harvested peat from fens, heaths, moors and bogs which were carefully managed and protected as common land for all to use. </p>
<p>From all these habitats, people had the right to cut peat for fuel and as a building material. Peat blocks were used for building walls; turf was used for roofing; and peat provided excellent insulation for walls and under floors. In some cases, entire buildings were carved out of the deeper peat within the land itself. </p>
<figure class="align-center ">
<img alt="Two people load chunks of solid earth into a cart." src="https://images.theconversation.com/files/359992/original/file-20200925-22-19acn61.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/359992/original/file-20200925-22-19acn61.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=717&fit=crop&dpr=1 600w, https://images.theconversation.com/files/359992/original/file-20200925-22-19acn61.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=717&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/359992/original/file-20200925-22-19acn61.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=717&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/359992/original/file-20200925-22-19acn61.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=901&fit=crop&dpr=1 754w, https://images.theconversation.com/files/359992/original/file-20200925-22-19acn61.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=901&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/359992/original/file-20200925-22-19acn61.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=901&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Peat fuel dug in Ireland during a coal shortage, 1947.</span>
<span class="attribution"><span class="source">Ian Rotherham</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Plants that grew in peatlands were also harvested. Cut willow, or “withies”, were used in construction, while reeds, sedges and rushes were used for thatching. And these habitats offered abundant grazing for livestock and wildfowl like geese, not to mention fish that thrived in ponds.</p>
<p>Peat turf smoulders gently, and helped keep some fires alight continuously for a century or more. The fuel is smoky and produces what became known as the “peat-reek” – a pungent smell that at least warded off the ubiquitous midges and mosquitoes.</p>
<p>These medieval wetlands were <a href="http://etheses.dur.ac.uk/10857/">rife with malaria</a> – a disease introduced to England by the Romans – and known as the marsh ague. Those raised in the Cambridgeshire Fens obtained <a href="https://core.ac.uk/download/pdf/207425184.pdf">a degree of immunity</a> to the disease, but suffered yellow jaundice due to the effects it wrought on their livers, and tended to be rather stunted in stature.</p>
<p>By the 19th and 20th centuries, traditional rights for commoners to freely use peatlands had been swept away by government acts of enclosure, which converted land into private property. Subsistence use morphed into commercial exploitation, and peat was sold door-to-door or at markets. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/359996/original/file-20200925-14-1sy5b6r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A black-and-white aerial photo of rural fields." src="https://images.theconversation.com/files/359996/original/file-20200925-14-1sy5b6r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/359996/original/file-20200925-14-1sy5b6r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/359996/original/file-20200925-14-1sy5b6r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/359996/original/file-20200925-14-1sy5b6r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/359996/original/file-20200925-14-1sy5b6r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/359996/original/file-20200925-14-1sy5b6r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/359996/original/file-20200925-14-1sy5b6r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The peat fields of Somerset, south-west England, 1972.</span>
<span class="attribution"><span class="source">Ian Rotherham</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Peat was taken as litter for the horses that powered growing towns and cities, and then for the war horses of the first world war. As the 20th century wore on, remaining peatlands were harvested on an industrial scale for compost to satisfy Britain’s burgeoning passion for gardening.</p>
<h2>The carbon record</h2>
<p>Despite their central role in the lives of our ancestors, peatlands have left little residue on our ideas of the past. So total was our collective amnesia around these important sites that a researcher in the 1950s shocked many by <a href="https://norfolkrecordofficeblog.org/2016/05/13/the-norfolk-broads-revealed-as-man-made-features-the-discoveries-of-dr-joyce-m-lambert/">disproving the idea</a> that the Norfolk Broads were a natural wilderness. Joyce Lambert of Cambridge University showed that the Broads – a network of rivers and lakes in the east of England – were actually excavated medieval peat deposits that were abandoned and flooded. Far from wild, this landscape was carved by human hands over many centuries. </p>
<p>The forgetfulness is particularly odd in Norfolk, where peat fuel was harvested in enormous quantities. Norwich, one of England’s major medieval cities, was fuelled by peat turf for centuries. Norwich Cathedral used 400,000 bricks of solid peat for fuel each year. This reached its peak in the 14th and 15th centuries, and amounted to over 80 million peat bricks burned over <a href="https://www.nature.com/articles/187636a0">two centuries</a>.</p>
<p>Today, sites that were <a href="https://www.ukeconet.org/store/p741/The_History_of_Domestic_Peat_Fuel_Exploitation_in_Relation_to_Carbon_%2526_Climate_Change.html">entirely stripped of peat</a> are common throughout the UK. Where peatlands once dwarfed entire landscapes, there are large stretches where no peat bogs exist.</p>
<figure class="align-center ">
<img alt="A man digs turg near a pond with a horse and cart nearby." src="https://images.theconversation.com/files/359986/original/file-20200925-22-pd6q3a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/359986/original/file-20200925-22-pd6q3a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=383&fit=crop&dpr=1 600w, https://images.theconversation.com/files/359986/original/file-20200925-22-pd6q3a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=383&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/359986/original/file-20200925-22-pd6q3a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=383&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/359986/original/file-20200925-22-pd6q3a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=482&fit=crop&dpr=1 754w, https://images.theconversation.com/files/359986/original/file-20200925-22-pd6q3a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=482&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/359986/original/file-20200925-22-pd6q3a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=482&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">In some areas, pockets of peatland are all that remain of once vast tracts.</span>
<span class="attribution"><span class="source">Ian Rotherham</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>All this exploitation released carbon dioxide, stored for thousands of years, to the atmosphere. Scientists have calculated that peat digging on Thorne Moors near Doncaster caused about <a href="https://www.ukeconet.org/store/p742/ESTIMATION_OF_THE_CARBON_CONTENT_OF_THE_HUMBERHEAD_LEVELS_WETLANDS_OVER_TIME_-_The_case_of_Thorne_Moors.html">16.6 million tonnes</a> of carbon to leak to the atmosphere from the 16th century onwards. That’s more than the annual output of <a href="https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator">15 coal-fired power stations</a> today. Peat digging around the world could have <a href="https://www.ukeconet.org/store/p741/The_History_of_Domestic_Peat_Fuel_Exploitation_in_Relation_to_Carbon_%26_Climate_Change.html">influenced the global climate</a> before the industrial revolution.</p>
<p>Putting all of that carbon back will be a challenge, as many former bogs are farmed. Peat-rich soils in the lowland bread basket of the UK supply the bulk of its domestically grown crops – and continue to haemorrhage carbon to the atmosphere. These arable farms on converted temperate peatlands are estimated to release <a href="https://www.worldcat.org/title/global-status-of-peatlands-and-their-role-in-carbon-cycling-a-report-for-friends-of-the-earth/oclc/60015973">41 tonnes of carbon dioxide</a> per hectare per year. And agriculture experts believe the fertility of these soils is being exhausted, with <a href="https://www.theguardian.com/environment/2017/oct/24/uk-30-40-years-away-eradication-soil-fertility-warns-michael-gove">fewer than 50 harvests left</a> in the peat-fen countryside across much of lowland England.</p>
<p>With so much demand on the land, from growing food, to building houses and generating energy, it’s tempting to ask why we should make room for peatlands. But peatlands once provided all of these things and more. Recasting them as an ally in the fight against climate change only scratches the surface of their future usefulness.</p><img src="https://counter.theconversation.com/content/139182/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian D. Rotherham does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The UK’s marshes, bogs and fens provided the bare necessities of daily life for many centuries.Ian D. Rotherham, Professor of Environmental Geography and Reader in Tourism and Environmental Change, Sheffield Hallam UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1510142020-11-27T16:11:41Z2020-11-27T16:11:41ZHow green is your Christmas tree?<figure><img src="https://images.theconversation.com/files/371748/original/file-20201127-19-d53my5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Paolo Paradiso / shutterstock</span></span></figcaption></figure><p>There’s no way around the fact that Christmas has a <a href="https://theconversation.com/five-ways-to-reduce-your-eco-footprint-this-christmas-51735">large carbon footprint</a>, from the travelling we do to the presents we give and the large amounts of food we eat. But it is possible to at least reduce the negative impacts. With climate change and carbon dioxide levels now major sources of concern, surely it is time to see what can be done to be friendlier to the environment, and the Christmas tree is a good place to start.</p>
<p>As editor of an academic journal on <a href="https://think.taylorandfrancis.com/special_issues/arboricultural-research-advancing-the-united-nations-sustainable-development-goals/">arboriculture</a> – the cultivation of trees – this is something I know a bit about. There are <a href="https://www.christmasforest.co.uk/pages/christmas-tree-sustainability">various aspects</a> to assess: how the trees are grown, how many years they are used for, and how they are disposed of or recycled. For artificial trees, we also need to consider what they are made of and how and where they are manufactured. </p>
<p>For real trees, there is a question of where they comes from and how they were grown. Sourcing your tree locally will cut down on transportation costs and emissions and support local jobs too. Habitat may be another issue, since trees grown on moors, heaths, and peat bogs are hugely damaging with <a href="https://www.routledge.com/Peatlands-Ecology-Conservation-and-Heritage/Rotherham/p/book/9781138343214">massive losses of peat-carbon</a> and biodiversity, and increased downstream flooding. It’s better to instead choose trees grown on arable fields or “improved” grassland of little ecological interest. </p>
<h2>Don’t worry about the emissions</h2>
<p>When buying a Christmas tree, people may worry about carbon dioxide released back into the atmosphere when it is cut down and then, once used, disposed of. But there are issues and complications with this. Yes, you are cutting down a young tree which will either be thinned from a plantation of larger trees or be part of a single-aged crop all cut down at the same time. In the first instance, the loss of your tree will make no difference whatsoever to the carbon balance of the plantation since the other trees nearby will grow in compensation because competition for light and nutrients is reduced.</p>
<p>Even when a tree has been harvested as part of a single-aged crop, a proportion of its organic matter (and carbon) will remain as the dead root material and fallen leaves to be reincorporated into the soil’s carbon-bank. And if you recycle the tree after use as woodchip, then all that material is returned to the soil as well, and only a small proportion will return immediately to the atmosphere. </p>
<p>If you burn the old tree, then clearly both carbon dioxide and other pollutants go immediately into the air. However, even in this scenario, your tree can only return to the atmosphere the carbon which it took out in the first place – so there is zero net carbon loss. Our real concerns for carbon release are from burning of fossil fuels from below ground, and from damage to long-term carbon storage in peat bogs and fens. Disposal at landfill is <a href="https://www.bbc.com/reel/video/p06twlb8/reality-check-your-christmas-tree-s-carbon-footprint">much more damaging</a> than incineration.</p>
<p>There is not much to choose between the different species of Christmas tree, at least in terms of carbon impact. There are issues, though, in terms of how trees are grown and particularly the <a href="https://www.theguardian.com/environment/2017/dec/10/the-eco-guide-to-christmas-trees">use of pesticides</a> in their cultivation, and potential damage to precious wildlife habitats. A recent example is the damage wrought to a peat bog in Cumbria by inappropriate planting of <a href="https://www.bbc.com/news/uk-england-cumbria-54971229">conifer trees</a>.</p>
<p>An artificial tree, on the other hand, can have a relatively significant carbon footprint depending on what it is made from, and most of all, how many years it remains in service. Spread over ten years, the impact is negligible, but if it has been manufactured abroad, then the immediate carbon footprint is considerable.</p>
<h2>How to reduce your tree’s footprint:</h2>
<p>1) Buy a real tree, put it in a pot and use it over several years and finally plant it outside to live on. That way you will even mop up a little of your carbon footprint from other Christmas celebrations.</p>
<p>2) Recycle your real tree after use as woodchip or compost. Don’t bin or burn it.</p>
<p>3) Buy local and from a charity.</p>
<p>4) Avoid trees brought in from a distance and especially from an environmentally damaging source – ask the retailer where they are from. Better still, go direct to a local farm shop or National Trust site that is both producing and selling trees.</p>
<p>5) Ask for organically grown trees if possible.</p>
<p>6) Some growers make a donation per tree to an environmental charity – so ask when you buy.</p>
<p>Any “consumption” of goods has environmental impacts, but that is an unavoidable part of life. Christmas trees provide lots of pleasure for many people – just try to boost the good aspects and avoid or minimise the bad ones.</p><img src="https://counter.theconversation.com/content/151014/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian D. Rotherham does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>It depends on where and how it’s grown, and how it is disposed of or recycled.Ian D. Rotherham, Professor of Environmental Geography and Reader in Tourism and Environmental Change, Sheffield Hallam UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1506622020-11-26T19:12:08Z2020-11-26T19:12:08ZClimate change is making autumn leaves change colour earlier – here’s why<figure><img src="https://images.theconversation.com/files/371524/original/file-20201126-17-6rujb9.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C6000%2C3979&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/5IHz5WhosQE">Chris Lawton/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>As the days shorten and temperatures drop in the northern hemisphere, leaves begin to turn. We can enjoy glorious autumnal colours while the leaves are still on the trees and, later, kicking through a red, brown and gold carpet when out walking.</p>
<p>When temperatures rise again in spring, the growing season for trees resumes. Throughout the warmer months, trees take carbon dioxide from the atmosphere and store it in complex molecules, releasing oxygen as a byproduct. This, in a nutshell, is the process of photosynthesis. The more photosynthesis, the more carbon is locked away.</p>
<p>We know that carbon dioxide is a major driver of climate change, so the more that can be taken out of the atmosphere by plants, the better. With the warmer climate leading to a longer growing season, some researchers have <a href="https://www.fs.fed.us/nrs/pubs/jrnl/2014/nrs_2014_keenan_001.pdf">suggested</a> that more carbon dioxide would be absorbed by trees and other plants than in previous times. But <a href="https://science.sciencemag.org/cgi/doi/10.1126/science.abd8911">a new study</a> has turned this theory on its head and could have profound effects on how we adapt to climate change.</p>
<h2>Reaching the limit</h2>
<p>The researchers, led by Deborah Zani at the Swiss Federal Institute of Technology, studied the degree to which the timing of colour changes in autumn tree leaves was determined by the growth of the plant in the preceding spring and summer. </p>
<p>Temperature and day length were traditionally accepted as the main determinants of when leaves changed colour and fell, leading <a href="http://max2.ese.u-psud.fr/publications/Delpierre_2009_AFM.pdf">some scientists</a> to assume that warming temperatures would delay this process until later in the season. Studying deciduous European tree species, including horse chestnut, silver birch and English oak, the authors of the new study recorded how much carbon each tree absorbed per season and how that ultimately affected when the leaves fell.</p>
<p>Using data from the <a href="https://www.researchgate.net/profile/Barbara_Templ/publication/323254030_Pan_European_Phenological_database_PEP725_a_single_point_of_access_for_European_data/links/5a8bf0dba6fdcc6b1a442ef2/Pan-European-Phenological-database-PEP725-a-single-point-of-access-for-European-data.pdf">Pan European Phenology
Project</a>, which has tracked some trees for as long as 65 years, the researchers found in their long-term observational study that as the rate of photosynthesis increased, leaves changed colour and fell earlier in the year. For every 10% increase in photosynthetic activity over the spring and summer growing season, trees shed their leaves, on average, eight days earlier.</p>
<p>Climate-controlled experiments on five-year-old European beech and Japanese meadowsweet trees suggest what could be behind this unexpected result. In these trials, the trees were exposed to full sun, half shade or full shade. The results show that there is a limit to the amount of photosynthesis that a tree can carry out over a growing season. Think of it like filling a bucket with water. It can be done slowly or quickly, but once the bucket is full, there is nowhere for any more water to go.</p>
<figure class="align-center ">
<img alt="A misty forest with trees displaying autumn colours." src="https://images.theconversation.com/files/371502/original/file-20201126-21-1rb5f4f.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5933%2C3959&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/371502/original/file-20201126-21-1rb5f4f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371502/original/file-20201126-21-1rb5f4f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371502/original/file-20201126-21-1rb5f4f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371502/original/file-20201126-21-1rb5f4f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371502/original/file-20201126-21-1rb5f4f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371502/original/file-20201126-21-1rb5f4f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Deciduous trees, which shed leaves in autumn, have a fixed amount of carbon they can absorb per season.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/colorful-tall-beech-trees-close-forest-1717461841">Alex Stemmer/Shutterstock</a></span>
</figcaption>
</figure>
<p>This research shows that deciduous trees can only absorb a set amount of carbon each year and once that limit is reached, no more can be absorbed. At that point, leaves begin to change colour. This limit is set by the availability of nutrients, particularly nitrogen, and the physical structure of the plant itself, particularly the inner vessels which move water and dissolved nutrients around. Nitrogen is a key nutrient which plants need in order to grow, and it’s often the amount of available nitrogen that limits total growth. This is why farmers and gardeners use nitrogen fertilisers, to overcome this limitation.</p>
<p>Together, these constraints mean that carbon uptake during the growing season is a self-regulating mechanism in <a href="https://www.pnas.org/content/111/20/7355">trees</a> and <a href="https://pubmed.ncbi.nlm.nih.gov/31158300/">herbaceous plants</a>. Only so much carbon can be taken up.</p>
<h2>Earlier autumn colours</h2>
<p>In a world with increasing levels of <a href="https://public.wmo.int/en/media/press-release/carbon-dioxide-levels-continue-record-levels-despite-covid-19-lockdown#:%7E:text=The%20annual%20globally%20averaged%20level,per%20million%20benchmark%20in%202015.">carbon in the atmosphere</a>, these new findings imply that warmer weather and longer growing seasons will not allow temperate deciduous trees to take up more carbon dioxide. The study’s predictive model suggests that by 2100, when tree growing seasons are expected to be between 22 and 34 days longer, leaves will fall from trees between three and six days earlier than they do now.</p>
<figure class="align-center ">
<img alt="A pile of yellow and orange maple leaves with a dark red leaf in the middle." src="https://images.theconversation.com/files/371523/original/file-20201126-21-1cmpnob.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/371523/original/file-20201126-21-1cmpnob.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371523/original/file-20201126-21-1cmpnob.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371523/original/file-20201126-21-1cmpnob.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371523/original/file-20201126-21-1cmpnob.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371523/original/file-20201126-21-1cmpnob.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371523/original/file-20201126-21-1cmpnob.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Get ready for this happening a little sooner in the future.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/kAc0En1s1h8">Greg Shield/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>This has significant implications for climate change modelling. If we accept that the amount of carbon taken up by deciduous trees in temperature countries like the UK will remain the same each year regardless of the growing season, carbon dioxide levels will rise more quickly than was previously expected. The only way to change this will be to increase the capacity of trees to absorb carbon. </p>
<p>Plants that aren’t limited by the amount of nitrogen available may be able to grow for longer in the warming climate. These are the trees which can take nitrogen from the air, such as <a href="https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/british-trees/a-z-of-british-trees/alder/">alder</a>. But these species will still lose their leaves at roughly the same time as always, thanks to less daylight and colder temperatures.</p>
<p>But on the upside, with the prospect of some trees losing their leaves earlier and others losing them at the time they do now, there might be the prospect of prolonged autumnal colours – and more time for us to kick through the leaves.</p><img src="https://counter.theconversation.com/content/150662/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Philip James does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Warmer temperatures cannot increase the amount of carbon deciduous trees absorb in each growing season, a new study suggests.Philip James, Professor of Ecology, University of SalfordLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1436202020-08-12T20:13:03Z2020-08-12T20:13:03ZFrom cave art to climate chaos: how a new carbon dating timeline is changing our view of history<figure><img src="https://images.theconversation.com/files/352428/original/file-20200812-23-cpm0hy.jpg?ixlib=rb-1.1.0&rect=150%2C110%2C6559%2C4355&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Geological and archaeological records offer important insights into what seems to be an increasingly uncertain future. </p>
<p>The better we understand what conditions Earth has already experienced, the better we can predict (and potentially prevent) future threats. </p>
<p>But to do this effectively, we need an accurate way to date what happened in the past. </p>
<p>Our research, published today in the journal <a href="https://www.cambridge.org/core/journals/radiocarbon/calibrations/intcal-20">Radiocarbon</a>, offers a way to do just that, through an updated method of calibrating the <a href="https://c14.arch.ox.ac.uk/dating.html">radiocarbon timescale</a>.</p>
<h2>An amazing tool for perusing the past</h2>
<p>Radiocarbon dating has revolutionised our understanding of the past. It is nearly 80 years since Nobel Prize-winning US chemist Willard Libby <a href="https://www.nature.com/articles/d41586-019-01895-z">first suggested</a> minute amounts of a radioactive form of carbon are created in the upper atmosphere. </p>
<p>Libby correctly argued this newly formed radiocarbon (or C-14) rapidly converts to carbon dioxide, is taken up by plants during photosynthesis, and from there travels up through the food chain. </p>
<p>When organisms interact with their environment while alive, they have the same proportion of C-14 as their environment. Once they die they stop taking in new carbon.</p>
<p>Their level of C-14 then halves every 5,730 years due to <a href="https://www.esrl.noaa.gov/gmd/ccgg/isotopes/decay.html">radioactive decay</a>. An organism that died yesterday will still have a high level of C-14, whereas one that died <a href="https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/radiocarbon-dating.html">tens of thousands of years ago will not</a>. </p>
<p>By measuring the level of C-14 in a specimen, we can deduce how long ago that organism died. Currently, with <a href="https://www.nature.com/articles/d41586-019-01895-z">this method</a>, we can date remains up to 60,000 years old.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-is-radiocarbon-dating-and-how-does-it-work-9690">Explainer: what is radiocarbon dating and how does it work?</a>
</strong>
</em>
</p>
<hr>
<h2>A seven-year effort</h2>
<p>If the level of C-14 in the atmosphere had always been constant, radiocarbon dating would be straightforward. But it hasn’t.</p>
<p>Changes in the <a href="https://wserv4.esc.cam.ac.uk/pastclimate/?page_id=19">carbon cycle</a>, impinging <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/cosmic-radiation">cosmic radiation</a>, the <a href="https://www.pnas.org/content/112/31/9542">use of fossil fuels</a> and <a href="https://theconversation.com/anthropocene-began-in-1965-according-to-signs-left-in-the-worlds-loneliest-tree-91993">20th century nuclear testing</a> have all caused large variations over time. Thus, all radiocarbon dates need to be adjusted (or calibrated) to be turned into accurate calendar ages.</p>
<p>Without this adjustment, dates could be out by up to 10-15%. <a href="https://www.cambridge.org/core/journals/radiocarbon/calibrations">This week we report</a> a seven-year international effort to recalculate three radiocarbon calibration curves: </p>
<ul>
<li>IntCal20 (“20” to signify this year) for objects from the northern hemisphere</li>
<li>SHCal20 for samples from the ocean-dominated southern hemisphere</li>
<li>Marine20 for samples from the world’s oceans.</li>
</ul>
<figure class="align-right ">
<img alt="Close-up of bristlecone pine tree rings." src="https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/352243/original/file-20200811-20-1ciaghc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">We dated bristlecone pine tree rings from the second millennium BC.</span>
<span class="attribution"><span class="source">P. Brewer/Uni of Arizona</span></span>
</figcaption>
</figure>
<p>We constructed these updated curves by measuring a plethora of materials that record past radiocarbon levels, but which can also be dated by other methods. </p>
<p>Included in the archives are tree rings from ancient logs preserved in wetlands, cave stalagmites, corals from the continental shelf and sediments drilled from lake and ocean beds. </p>
<figure class="align-center ">
<img alt="An ancient New Zealand kauri tree log." src="https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/351532/original/file-20200806-24-1vpdpwj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Ancient New Zealand kauri (<em>Agathis australis</em>) logs like this example were used to help construct the calibration curves. This tree is about 40,000 years old and was found buried underground.</span>
<span class="attribution"><span class="source">Nelson Parker</span></span>
</figcaption>
</figure>
<p>In total, the new curves are based on almost 15,000 radiocarbon measurements taken from objects up to 60,000 years old.</p>
<p>Advances in radiocarbon measurement using <a href="https://en.wikipedia.org/wiki/Accelerator_mass_spectrometry">accelerator mass spectrometry</a> mean the updated curves can use very small samples, such as single tree rings from just one year’s growth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Close-up of an ancient stalagmite." src="https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=177&fit=crop&dpr=1 600w, https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=177&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=177&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=223&fit=crop&dpr=1 754w, https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=223&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/352423/original/file-20200812-20-685xzm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=223&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Stalagmites from inside the Hulu Cave in China were key to estimating the amount of radiocarbon present in objects between 14,000 and 55,000 years old.</span>
<span class="attribution"><span class="source">Hai Cheng</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Reassessing old beliefs</h2>
<p>The new radiocarbon calibration curves provide previously impossible precision and detail. As a result, they greatly improve our understanding of how Earth has evolved and how these changes impacted its inhabitants.</p>
<p>One example is the rate of environmental change at the end of the most recent ice age. As the world started to warm some 18,000 years ago, vast ice sheets covering Antarctica, North America (including Greenland) and Europe melted – returning huge volumes of fresh water to the oceans.</p>
<p>But the sea level didn’t rise at a consistent rate like the global temperature. Sometimes it was gradual and other times extremely rapid.</p>
<p>A prime location to detect past sea levels is the <a href="https://www.britannica.com/place/Sunda-Shelf">Sunda Shelf</a>, a large platform of land that was once part of continental Southeast Asia.</p>
<p><a href="https://science.sciencemag.org/content/288/5468/1033.full">One study</a> published in 2000 showed mangrove plant remains found on the seabed recorded a catastrophic 16-metre sea level rise over several hundred years (about half a metre each decade). This event, known as <a href="https://www.giss.nasa.gov/research/briefs/gornitz_10/">Meltwater Pulse-1A</a>, flooded the Sunda Shelf. </p>
<p>Our latest work has modified this story considerably. The new calibration curves reveal this extreme phase of sea level rise actually began 14,640 years ago and lasted just 160 years. </p>
<p>This equates to a staggering one-metre rise each decade – a sobering lesson for the future, considering the current much lower <a href="https://www.theguardian.com/environment/2020/may/08/sea-levels-could-rise-more-than-a-metre-by-2100-experts-say">projected changes for the end of this century</a>. </p>
<h2>An extra half a millennium of art</h2>
<p>Going further back in time, we also looked at some of the world’s oldest cave art in France’s <a href="https://archeologie.culture.fr/chauvet/en">Chauvet Cave</a>, first discovered in 1994. </p>
<p>This cave contains hundreds of beautifully preserved paintings. They depict a European menagerie with long-extinct mammoths, cave lions and woolly rhinoceroses, captured in real-life scenes that provide a window into a lost world.</p>
<p>The Chauvet Cave reveals the artistic sophistication of our <a href="http://www.bradshawfoundation.com/chauvet/index.php">early ancestors</a> in phenomenal detail.</p>
<figure class="align-center ">
<img alt="Chauvet cave paintings depicting wild animals including horses." src="https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=595&fit=crop&dpr=1 600w, https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=595&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=595&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=747&fit=crop&dpr=1 754w, https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=747&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/351623/original/file-20200806-20-11fv1gc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=747&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Chauvet Cave contains hundreds of cave paintings created more than 30,000 years ago.</span>
<span class="attribution"><span class="source">Thomas T/flickr</span></span>
</figcaption>
</figure>
<p>With the new IntCal20 curve, our best estimate for the creation of the oldest radiocarbon-dated painting in the cave is now 36,500 years ago. This is almost 450 years older than previously thought.</p>
<p>These are just two of many more examples of the far-reaching impact our latest work will have. </p>
<p>As <a href="https://www.cambridge.org/core/journals/radiocarbon/calibrations">the new calibration curves</a> are used to re-analyse ages of a host of archaeological and geological records, we can expect major shifts in our understanding of the planet’s past – and hopefully, a better forecast into its future. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/is-that-rock-hashtag-really-the-first-evidence-of-neanderthal-art-31238">Is that rock hashtag really the first evidence of Neanderthal art?</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/143620/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Turney receives funding from The Australian Research Council and is a scientific advisor to cleantech graphite company, CarbonScape (<a href="https://www.carbonscape.com">https://www.carbonscape.com</a>).</span></em></p><p class="fine-print"><em><span>Alan Hogg receives funding from the Marsden fund administered by the Royal Society of New Zealand. </span></em></p><p class="fine-print"><em><span>Paula J. Reimer receives funding from the Leverhulme Trust and UK Research and Innovation. </span></em></p><p class="fine-print"><em><span>Tim Heaton receives funding from the Leverhulme Trust via a research fellowship on "Improving the Measurement of Time via Radiocarbon". </span></em></p>The updated methods are providing a clearer picture of how Earth and its inhabitants evolved over the past 60,000 years - and thus, providing new insight into its future.Christian Turney, Professor, Earth Science and Climate Change, UNSW SydneyAlan Hogg, Professor, Director, Carbon Dating Laboratory, University of WaikatoPaula J. Reimer, Chair professor, Queen's University BelfastTim Heaton, Lecturer in Statistics, University of SheffieldLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1398132020-07-30T11:08:26Z2020-07-30T11:08:26ZAre young trees or old forests more important for slowing climate change?<figure><img src="https://images.theconversation.com/files/349969/original/file-20200728-27-168b73l.jpg?ixlib=rb-1.1.0&rect=0%2C349%2C4240%2C2475&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/RVvr_g5-u3M">Jeremy Kieran/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Forests are thought to be crucial in the fight against climate change – and with good reason. We’ve known for a long time that the extra CO₂ humans are putting in the atmosphere <a href="https://nph.onlinelibrary.wiley.com/doi/full/10.1111/j.1469-8137.2004.01224.x">makes trees grow faster</a>, taking a large portion of that CO₂ back out of the atmosphere and storing it in wood and soils.</p>
<p>But a recent finding that the world’s forests are on average getting “<a href="https://www.nationalgeographic.com/science/2020/05/grand-old-trees-are-dying-leaving-forests-younger-shorter/">shorter and younger</a>” could imply that the opposite is happening. Adding further confusion, another study recently found that young forests take up more CO₂ globally <a href="https://www.pnas.org/content/116/10/4382">than older forests</a>, perhaps suggesting that new trees planted today could offset our carbon sins more effectively than ancient woodland.</p>
<p>How does a world in which forests are getting younger and shorter fit with one where they are also growing faster and taking up more CO₂? Are old or young forests more important for slowing climate change? We can answer these questions by thinking about the lifecycle of forest patches, the proportion of them of different ages and how they all respond to a changing environment.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/using-forests-to-manage-carbon-a-heated-debate-81363">Using forests to manage carbon: a heated debate</a>
</strong>
</em>
</p>
<hr>
<h2>The forest carbon budget</h2>
<p>Let’s start by imagining the world before humans began clearing forests and burning fossil fuels.</p>
<p>In this world, trees that begin growing on open patches of ground grow relatively rapidly for their first several decades. The less successful trees are crowded out and die, but there’s much more growth than death overall, so there is a net removal of CO₂ from the atmosphere, locked away in new wood.</p>
<p>As trees get large two things generally happen. One, they become more vulnerable to other causes of death, such as storms, <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.15227">drought</a> or <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.15227">lightning</a>. Two, they may start to run out of nutrients or get too tall to transport water efficiently. As a result, their net uptake of CO₂ slows down and can approach zero.</p>
<p>Eventually, our patch of trees is disturbed by some big event, like a landslide or fire, killing the trees and opening space for the whole process to start again. The carbon in the dead trees is gradually returned to the atmosphere as they decompose.</p>
<p>The vast majority of the carbon is held in the patches of big, old trees. But in this pre-industrial world, the ability of these patches to continue taking up more carbon is weak. Most of the ongoing uptake is concentrated in the younger patches and is balanced by CO₂ losses from disturbed patches. The forest is carbon neutral.</p>
<figure class="align-center ">
<img alt="A misty forest scene." src="https://images.theconversation.com/files/349952/original/file-20200728-31-13mo375.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C6000%2C3997&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/349952/original/file-20200728-31-13mo375.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/349952/original/file-20200728-31-13mo375.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/349952/original/file-20200728-31-13mo375.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/349952/original/file-20200728-31-13mo375.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/349952/original/file-20200728-31-13mo375.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/349952/original/file-20200728-31-13mo375.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">New trees absorb lots of carbon, old trees store more overall and dead trees shed their carbon to the atmosphere.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/fhrZLt7p-iQ">Greg Rosenke/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Now enter humans. The world today has a greater area of young patches of forest than we would naturally expect because historically, we have harvested forests for wood, or converted them to farmland, <a href="https://theconversation.com/rewilding-as-farmland-and-villages-are-abandoned-forests-wolves-and-bears-are-returning-to-europe-119316">before allowing them to revert back to forest</a>. Those clearances and harvests of old forests released a lot of CO₂, but when they are allowed to regrow, the resulting young and relatively short forest will continue to remove CO₂ from the atmosphere until it regains its neutral state. In effect, we forced the forest to lend some CO₂ to the atmosphere and the atmosphere will eventually repay that debt, but not a molecule more.</p>
<p>But adding extra CO₂ into the atmosphere, as humans have done so recklessly since the dawn of the industrial revolution, changes the total amount of capital in the system.</p>
<p>And the forest has been taking its share of that capital. We know from <a href="https://nph.onlinelibrary.wiley.com/doi/full/10.1111/j.1469-8137.2004.01224.x">controlled experiments</a> that higher atmospheric CO₂ levels enable trees to grow faster. The extent to which the full effect is realised in real forests <a href="https://doi.org/10.1038/s41586-020-2128-9">varies</a>. But <a href="https://www.pnas.org/content/early/2014/12/25/1407302112">computer models</a> and <a href="https://www.nature.com/articles/s41586-020-2035-0">observations</a> agree that faster tree growth due to elevated CO₂ in the atmosphere is currently causing a large carbon uptake. So, more CO₂ in the atmosphere is causing both young and old patches of forest to take up CO₂, and this <a href="https://www.pnas.org/content/116/10/4382">uptake is larger</a> than that caused by previously felled forests regrowing.</p>
<h2>The effect of climate change</h2>
<p>But the implications of climate change are quite different. All else being equal, <a href="https://science.sciencemag.org/content/368/6494/eaaz9463">warming tends to increase the likelihood of death</a> among trees, from drought, wildfire or insect outbreaks. This will lower the average age of trees as we move into the future. But, in this case, that younger age does not have a loan-like effect on CO₂. Those young patches of trees may take up CO₂ more strongly than the older patches they replace, but this is more than countered by the increased rate of death. The capacity of the forest to store carbon has been reduced. Rather than the forest loaning CO₂ to the atmosphere, it’s been forced to make a donation.</p>
<p>So increased tree growth from CO₂ and increased death from warming are in competition. In the tropics at least, increased growth is still outstripping increased mortality, meaning that these forests continue to take up huge amounts of carbon. <a href="https://www.nature.com/articles/s41586-020-2035-0">But the gap is narrowing</a>. If that uptake continues to slow, it would mean more of our CO₂ emissions stay in the atmosphere, accelerating climate change. </p>
<p>Overall, both young and old forests play important roles in slowing climate change. Both are taking up CO₂, primarily because there is more CO₂ about. Young forests take up a bit more, but this is largely an accident of history. The extra carbon uptake we get from having a relatively youthful forest will diminish as that forest ages. We can plant new forests to try to generate further uptake, <a href="https://theconversation.com/reforesting-an-area-the-size-of-the-us-needed-to-help-avert-climate-breakdown-say-researchers-are-they-right-119842">but space is limited</a>. </p>
<p>But it’s important to separate the question of uptake from that of storage. The world’s big, old forests store an enormous amount of carbon, keeping it out of the atmosphere, and will continue to do so, even if their net CO₂ uptake decreases. So long as they are not cut down or burned to ashes, that is.</p><img src="https://counter.theconversation.com/content/139813/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tom Pugh receives funding from the European Research Council through the TreeMort project. </span></em></p>The age of a forest can influence how effectively it offsets our emissions.Tom Pugh, Reader in Biosphere-Atmosphere Exchange, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1424622020-07-16T12:12:24Z2020-07-16T12:12:24ZAn effective climate change solution may lie in rocks beneath our feet<figure><img src="https://images.theconversation.com/files/347714/original/file-20200715-31-u81v6h.jpg?ixlib=rb-1.1.0&rect=4%2C4%2C2991%2C1989&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Weathering of rocks like these basalt formations in Idaho triggers chemical processes that remove carbon dioxide from the air.</span> <span class="attribution"><a class="source" href="https://flic.kr/p/2hMZxfS">Matthew Dillon/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Why has Earth’s climate remained so stable over geological time? The answer just might rock you. </p>
<p>Rocks, particularly the types created by volcanic activity, play a critical role in keeping Earth’s long-term climate stable and cycling carbon dioxide between land, oceans and the atmosphere.</p>
<p>Scientists have known for <a href="https://doi.org/10.1029/JC086iC10p09776">decades</a> that rock weathering – the chemical breakdown of minerals in mountains and soils – removes carbon dioxide from the atmosphere and transforms it into stable minerals on the planet’s surface and in ocean sediments. But because this process operates over millions of years, it is too weak to offset modern global warming from human activities.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/347727/original/file-20200715-37-1s7y6p6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Acid rain damage to buildings and monuments, like this sandstone statue in Dresden, Germany, is a form of chemical weathering.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Acid_rain#/media/File:Skulptur_aus_Sandstein,_Dresden_2012-09-06-0555.jpg">Slick/Wikipedia</a></span>
</figcaption>
</figure>
<p>Now, however, emerging science – including at the California Collaborative for Climate Change Solutions’ (C4) <a href="https://www.workinglandsinnovation.com/">Working Lands Innovation Center</a> – shows that it is possible to accelerate rock weathering rates. Enhanced rock weathering could both slow global warming and improve soil health, making it possible to grow crops more efficiently and bolster food security. </p>
<h2>Rock chemistry</h2>
<p>Many processes <a href="https://www.nationalgeographic.org/encyclopedia/weathering/">weather rocks</a> on Earth’s surface, influenced by chemistry, biology, climate and plate tectonics. The dominant form of chemical weathering occurs when carbon dioxide combines with water in the soil and the ocean to make carbonic acid. </p>
<p>About 95% of Earth’s crust and <a href="https://www.britannica.com/science/Earths-mantle">mantle</a> – the thick layer between the planet’s crust and its core – is made of <a href="https://www.britannica.com/science/silicate-mineral">silicate minerals</a>, which are compounds of silicon and oxygen. Silicates are the main ingredient in most igneous rocks, which form when volcanic material cools and hardens. Such rocks make up about 15% of Earth’s <a href="https://en.wikipedia.org/wiki/Igneous_rock#Geological_significance">land surface</a>. </p>
<p>When carbonic acid comes in contact with certain silicate minerals, it triggers a chemical process known as the <a href="https://doi.org/10.3389/fspas.2019.00062">Urey reaction</a>. This reaction pulls gaseous carbon dioxide from the atmosphere and combines it with water and calcium or magnesium silicates, producing two bicarbonate ions. Once the carbon dioxide is trapped in these soil carbonates, or ultimately washed into the ocean, it no longer warms the climate.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=333&fit=crop&dpr=1 600w, https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=333&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=333&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=418&fit=crop&dpr=1 754w, https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=418&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/347723/original/file-20200715-35-oit8oh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=418&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When carbonic acid dissolves calcium and magnesium silicate minerals, they break down into dissolved compounds, some of which contain carbon. These materials can flow to the ocean, where marine organisms use them to build shells. Later the shells are buried in ocean sediments. Volcanic activity releases some carbon back to the atmosphere, but much of it stays buried in rock for millions of years.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Carbonate%E2%80%93silicate_cycle#/media/File:Carbon-Slicate_Cycle_Feedbacks.jpg">Gretashum/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The Urey reaction runs at a higher rate when silicate-rich mountains such as the Himalayas expose fresh material to the atmosphere – for example, after a landslide – or when the climate becomes hotter and moister. Recent research demonstrates that humans can speed up the process substantially to help fight modern global warming.</p>
<h2>Accelerated weathering</h2>
<p>The biggest limit on weathering is the amount of silicate minerals exposed at any given time. Grinding up volcanic silicate rocks into a fine powder increases the surface area available for reactions. Further, adding this rock dust to the soil exposes it to plant roots and soil microbes. Both roots and microbes produce carbon dioxide as they decompose organic matter in the soil. In turn, this increases carbonic acid concentrations that accelerate weathering.</p>
<p>One recent study by British and Americans scientists suggests that adding finely crushed silicate rock, such as basalt, to all cropland soil in China, India, the U.S. and Brazil could trigger weathering that would remove <a href="https://doi.org/10.1038/s41586-020-2448-9">more than 2 billion tons of carbon dioxide</a> from the atmosphere each year. For comparison, the U.S. emitted <a href="https://www.nytimes.com/2019/01/08/climate/greenhouse-gas-emissions-increase.html">about 5.3 billion tons</a> of carbon dioxide in 2018. </p>
<p>[<em>Get our best science, health and technology stories.</em> <a href="https://theconversation.com/us/newsletters/science-editors-picks-71/?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=science-best">Sign up for The Conversation’s science newsletter</a>.]</p>
<h2>Farming with rocks</h2>
<p>One compelling aspect of enhanced weathering is that, in controlled-environment studies involving basalt amendments of soil, cereal grain yields are improved by <a href="https://doi.org/10.1111/gcb.15089">roughly 20%</a>. </p>
<p>As basalt weathers, it increases vital plant nutrients that can boost production and increase crops yields. Mineral nutrients such as calcium, potassium and magnesium create healthier soils. Farmers have been <a href="http://dx.doi.org/10.1590/S0001-37652006000400009">amending soil with rock minerals for centuries</a>, so the concept is nothing new. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/347717/original/file-20200715-29-x3wxdd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Spreading lime on a field in Devon, England to improve soil quality.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Spreading_lime_on_a_Devon_field.jpg">Mark Robinson/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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</figure>
<p>At the <a href="https://www.workinglandsinnovation.com/">Working Lands Innovation Center</a>, we are conducting perhaps the largest enhanced weathering demonstration experiment on real farms in the world. We are partnering with farmers, ranchers, government, the mining industry and Native American tribes in California on some 50 acres of cropland soil amendment trials. We are testing the effects of rock dust and compost amendments on greenhouse gas emissions from the soil, carbon capture, crop yields, and plant and microbial health. </p>
<p>Our initial results suggest that adding basalt and <a href="https://www.britannica.com/science/wollastonite">wollastonite</a>, a calcium silicate mineral, increased corn yields by 12% in the first year. Working with <a href="https://ww2.arb.ca.gov/our-work/programs/cap-and-trade-program">California’s greenhouse gas emissions trading program</a> and our state’s diverse agricultural interests, we hope to establish a pathway that would offer monetary incentives to farmers and ranchers who allow enhanced rock weathering on their lands. We aim to create a protocol for farmers and ranchers to make money from the carbon they farm into the soil and help businesses and industry achieve their carbon neutrality goals. </p>
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<h2>Why negative emissions matter</h2>
<p>Under the <a href="https://theconversation.com/paris-agreement-on-climate-change-the-good-the-bad-and-the-ugly-52242">2015 Paris climate agreement</a>, nations have pledged to limit global warming to less then 2 degrees Celsius above preindustrial levels. This will require massive cuts in greenhouse gas emissions.</p>
<p>Pulling carbon dioxide from the air – also known as negative emissions – is also necessary to avoid the worst climate change outcomes, because atmospheric carbon dioxide has an <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter06_FINAL.pdf">average lifespan of more than 100 years</a>. Every molecule of carbon dioxide that is released to the atmosphere through fossil fuel combustion or land clearing will remain there for many decades trapping heat and warming Earth’s surface.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/4IUQn9uL6W0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">In an even faster version of enhanced weathering, scientists pump supercritical carbon dioxide underground into basalt formations, where it reacts with minerals to form new solid rock.</span></figcaption>
</figure>
<p>Nations need a portfolio of solutions to create <a href="https://www.nap.edu/catalog/25259/negative-emissions-technologies-and-reliable-sequestration-a-research-agenda">negative emissions</a>. Enhanced weathering is poised for rapid scale-up, taking advantage of farm equipment that’s already in place, global mining operations and supply chains that currently deliver fertilizers and seeds worldwide. By addressing soil erosion and food security along with climate change, I believe rock weathering can help humans escape the hard place we find ourselves in today.</p><img src="https://counter.theconversation.com/content/142462/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Benjamin Z. Houlton receives funding from the California Strategic Growth Council</span></em></p>To avoid global warming on a catastrophic scale, nations need to reduce emissions and find ways to pull carbon from the air. One promising solution: spreading rock dust on farm fields.Benjamin Z. Houlton, Professor of Global Environmental Studies, Chancellor's Fellow and Director, John Muir Institute of the Environment, University of California, DavisLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1398412020-06-15T07:09:17Z2020-06-15T07:09:17ZPlanting non-native trees accelerates the release of carbon back into the atmosphere<figure><img src="https://images.theconversation.com/files/341053/original/file-20200611-114124-931x7i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">native forest</span> </figcaption></figure><p>Large-scale <a href="https://www.washingtonpost.com/graphics/2020/climate-solutions/trillion-tree-reforestation-climate-change-philippines/">reforestation projects</a> such as New Zealand’s <a href="https://www.teururakau.govt.nz/funding-and-programmes/forestry/one-billion-trees-programme/">One Billion Trees programme</a> are underway in many countries to help sequester carbon from the atmosphere. </p>
<p>But there is <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14887">ongoing debate</a> about whether to prioritise native or non-native plants to fight climate change. As our recent <a href="https://science.sciencemag.org/content/368/6494/967">research</a> shows, non-native plants often grow faster compared to native plants, but they also decompose faster and this helps to accelerate the release of 150% more carbon dioxide from the soil.</p>
<p>Our results highlight a challenging gap in our understanding of carbon cycling in newly planted or regenerating forests. </p>
<p>It is relatively easy to measure plant biomass (how quickly a plant grows) and to estimate how much carbon dioxide it has removed from the atmosphere. But measuring carbon release is more difficult because it involves complex interactions between the plant, plant-eating insects and soil microorganisms.</p>
<p>This lack of an integrated carbon cycling model that includes species interactions makes predictions for carbon budgeting exceedingly difficult.</p>
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<strong>
Read more:
<a href="https://theconversation.com/coldplay-conundrum-how-to-reduce-the-risk-of-failure-for-environmental-projects-99449">Coldplay conundrum: how to reduce the risk of failure for environmental projects</a>
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<h2>How non-native plants change the carbon cycle</h2>
<p>There is uncertainty in our climate forecasting because we don’t fully understand how the factors that influence carbon cycling - the process in which carbon is both accumulated and lost by plants and soils - differ across ecosystems.</p>
<p>Carbon sequestration projects typically use fast-growing plant species that accumulate carbon in their tissues rapidly. Few projects focus on what goes on in the soil.</p>
<p>Non-native plants often <a href="https://www.annualreviews.org/doi/full/10.1146/annurev-ecolsys-102209-144650">accelerate carbon cycling</a>. They usually have less dense tissues and can grow and incorporate carbon into their tissues faster than native plants. But they also decompose more readily, <a href="https://www.researchgate.net/publication/51402506_Plant_species_traits_are_the_predominant_control_on_litter_decomposition_rates_within_biomes_worldwide">increasing carbon release</a> back to the atmosphere.</p>
<p>Our research, recently published in the journal <a href="https://science.sciencemag.org/content/368/6494/967">Science</a>, shows that when non-native plants arrive in a new place, they establish new interactions with soil organisms. So far, <a href="https://www.researchgate.net/publication/7074562_Biotic_interactions_and_plant_invasions">research</a> has mostly focused on how this resetting of interactions with soil microorganisms, herbivorous insects and other organisms helps exotic plants to invade a new place quickly, often overwhelming native species.</p>
<p>Invasive non-native plants have already become a <a href="https://www.sciencedirect.com/science/article/abs/pii/S0169534712001747">major problem worldwide</a>, and are changing the <a href="https://www.researchgate.net/publication/51146313_Ecological_impacts_of_invasive_alien_plants_A_meta-analysis_of_their_effects_on_species_communities_and_ecosystems">composition and function of entire ecosystems</a>. But it is less clear how the interactions of invasive non-native plants with other organisms affect carbon cycling. </p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/climate-explained-how-different-crops-or-trees-help-strip-carbon-dioxide-from-the-air-123590">Climate explained: how different crops or trees help strip carbon dioxide from the air</a>
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<h2>Planting non-native trees releases more carbon</h2>
<p>We established 160 experimental plant communities, with different combinations of native and non-native plants. We collected and reared herbivorous insects and created identical mixtures which we added to half of the plots.</p>
<p>We also cultured soil microorganisms to create two different soils that we split across the plant communities. One soil contained microorganisms familiar to the plants and another was unfamiliar.</p>
<p>Herbivorous insects and soil microorganisms feed on live and decaying plant tissue. Their ability to grow depends on the nutritional quality of that food. We found that non-native plants provided a better food source for herbivores compared with native plants – and that resulted in more plant-eating insects in communities dominated by non-native plants.</p>
<p>Similarly, exotic plants also raised the abundance of soil microorganisms involved in the rapid decomposition of plant material. This synergy of multiple organisms and interactions (fast-growing plants with less dense tissues, high herbivore abundance, and increased decomposition by soil microorganisms) means that more of the plant carbon is released back into the atmosphere.</p>
<p>In a practical sense, these soil treatments (soils with microorganisms familiar vs. unfamiliar to the plants) mimic the difference between reforestation (replanting an area) and afforestation (planting trees to create a new forest).</p>
<p>Reforested areas are typically replanted with native species that occurred there before, whereas afforested areas are planted with new species. Our results suggest planting non-native trees into soils with microorganisms they have never encountered (in other words, afforestation with non-native plants) may lead to more rapid release of carbon and undermine the effort to mitigate climate change.</p><img src="https://counter.theconversation.com/content/139841/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lauren Waller receives funding from the Tertiary Education Council. </span></em></p><p class="fine-print"><em><span>Warwick Allen was supported by Centre of Research Excellence funding from the Tertiary Education Commission. </span></em></p>Tree planting projects that use non-native trees risk releasing more carbon back into the atmosphere, undermining efforts to fight climate change.Lauren Waller, Postdoctoral Fellow, Lincoln University, New ZealandWarwick Allen, Postdoctoral fellow, University of CanterburyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1378742020-05-12T19:46:22Z2020-05-12T19:46:22ZClimate explained: what caused major climate change in the past?<figure><img src="https://images.theconversation.com/files/334197/original/file-20200512-66649-5piok4.jpg?ixlib=rb-1.1.0&rect=81%2C134%2C3813%2C2295&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p><em><strong><a href="https://theconversation.com/nz/topics/climate-explained-74664">Climate Explained</a></strong> is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.</em> </p>
<p><em>If you have a question you’d like an expert to answer, please send it to climate.change@stuff.co.nz</em></p>
<blockquote>
<p><strong>Earth had several periods of high carbon dioxide levels in the atmosphere and high temperatures over the last several million years. Can you explain what caused these periods, given that there was no burning of fossil fuels or other sources of human created carbon dioxide release during those times?</strong></p>
</blockquote>
<p>Burning fossil fuels or vegetation is one way to put carbon dioxide into the air – and it is something we have become very good at. Humans are generating <a href="https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions#how-have-global-co2-emissions-changed-over-time">nearly 40 billion tons of carbon dioxide</a> every year, mostly by burning fossil fuels. </p>
<p>Carbon dioxide stays in the air <a href="https://earthobservatory.nasa.gov/features/CarbonCycle/page5.php">for centuries to millennia</a> and it builds up over time. Since we began the systematic use of coal and oil for fuel, around 300 years ago, the amount of carbon dioxide in the air has gone up by almost half.</p>
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<img alt="" src="https://images.theconversation.com/files/334194/original/file-20200512-66698-lns3wx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/334194/original/file-20200512-66698-lns3wx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=369&fit=crop&dpr=1 600w, https://images.theconversation.com/files/334194/original/file-20200512-66698-lns3wx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=369&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/334194/original/file-20200512-66698-lns3wx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=369&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/334194/original/file-20200512-66698-lns3wx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=463&fit=crop&dpr=1 754w, https://images.theconversation.com/files/334194/original/file-20200512-66698-lns3wx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=463&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/334194/original/file-20200512-66698-lns3wx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=463&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="attribution"><span class="source">NOAA</span></span>
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<p>Apart from the emissions we add, carbon dioxide concentrations in the air go up and down as part of the natural <a href="https://earthobservatory.nasa.gov/features/CarbonCycle">carbon cycle</a>, driven by exchanges between the air, the oceans and the biosphere (life on earth), and ultimately by geological processes. </p>
<h2>Natural changes in carbon dioxide</h2>
<p>Every year, carbon dioxide concentrations rise and fall a little as plants grow in spring and summer and die off in the autumn and winter. The timing of this <a href="https://niwa.co.nz/atmosphere/our-data/trace-gas-plots/carbon-dioxide">seasonal rise and fall</a> is tied to northern hemisphere seasons, as most of the land surface on Earth is there. </p>
<p>The oceans also play an active role in the carbon cycle, contributing to variations over a few months to slow shifts over centuries. Ocean water takes up carbon dioxide directly in an exchange <a href="https://sos.noaa.gov/datasets/ocean-atmosphere-co2-exchange/">between the air and seawater</a>. Tiny marine plants use carbon dioxide for photosynthesis and many microscopic marine organisms use carbon compounds to make shells. When these marine micro-organisms die and sink to the seafloor, they take the carbon with them.</p>
<p>Collectively, the biosphere (ecosystems on land and in soils) and the oceans are absorbing about <a href="https://worldoceanreview.com/en/wor-1/ocean-chemistry/co2-reservoir/">half of all human-emitted carbon dioxide</a>, and this slows the rate of climate change. But as the climate continues to change and the oceans warm up further, it is not clear whether the biosphere and oceans will continue absorbing such a large fraction of our emissions. As water warms, it is less able to absorb carbon dioxide, and as the climate changes, many ecosystems become stressed and are less able to photosynthesise carbon dioxide.</p>
<h2>Earth’s deep climate history</h2>
<p>On time scales of hundreds of thousands to millions of years, carbon dioxide concentrations in the air have varied hugely, and so has global climate. </p>
<p>This <a href="https://www.skepticalscience.com/weathering.html">long-term carbon cycle</a> involves the formation and decay of the Earth’s surface itself: tectonic plate activity, the build-up and weathering of mountain chains, prolonged volcanic activity, and the emergence of new seafloor at active mid-ocean faults. </p>
<p>Most of the carbon stored in the Earth’s crust is in the form of limestone, created from the carbon-based shells of marine organisms that sank to the ocean floor millions of year ago.</p>
<p>Carbon dioxide is added to the air when volcanoes erupt, and it is taken out of the air as rocks and mountain ranges weather and wear down. These processes typically take millions of years to add or subtract carbon dioxide from the atmosphere. </p>
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Read more:
<a href="https://theconversation.com/climate-explained-how-volcanoes-influence-climate-and-how-their-emissions-compare-to-what-we-produce-125490">Climate explained: how volcanoes influence climate and how their emissions compare to what we produce</a>
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<hr>
<p>In the present day, volcanoes add only a little carbon dioxide to the air, around <a href="https://www.skepticalscience.com/volcanoes-and-global-warming.htm">1% of what human activity is currently contributing</a>. But there have been times in the past where volcanic activity has been vastly greater and has spewed large amounts of carbon dioxide into the air.</p>
<p>An example is around 250 million years ago, when prolonged volcanic activity raised atmospheric carbon dioxide levels dramatically. These were volcanic eruptions on a vast scale - lasting for around two million years and <a href="https://www.sciencedaily.com/releases/2017/10/171002105227.htm">causing a mass extinction</a>.</p>
<p>In the more recent geological past, the past 50 million years, carbon dioxide levels have been gradually dropping overall and the climate has been cooling, with some ups and downs. Once carbon dioxide concentrations became low enough (around 300 parts per million) between two and three million years ago, the current ice age cycle began, but the warming our emissions are causing is larger than the natural cooling trend. </p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/climate-explained-why-we-wont-be-heading-into-an-ice-age-any-time-soon-123675">Climate explained: why we won't be heading into an ice age any time soon</a>
</strong>
</em>
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<p>While Earth’s climate has changed significantly in the past, it happened on geological time scales. The carbon in the oil and coal we burn represents carbon dioxide taken up by vegetation hundreds of millions of years ago and then deposited through geological processes over millennia. We have burned a significant proportion within a few centuries.</p>
<p>If human emissions of carbon dioxide continue to increase through this century, we could reach levels <a href="https://e360.yale.edu/features/how-the-world-passed-a-carbon-threshold-400ppm-and-why-it-matters">not seen for tens of millions of years</a>, when Earth had a much warmer climate with much higher sea levels and no ice sheets.</p><img src="https://counter.theconversation.com/content/137874/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Renwick receives funding from the NZ Ministry for Business, Innovation and Employment. He is affiliated with the NZ Climate Change Commission. </span></em></p>Earth’s has gone through major climate changes in the past. They happened on time scales of millions of years and triggered mass extinctions. Our emissions are changing the climate much faster.James Renwick, Professor, Physical Geography (climate science), Te Herenga Waka — Victoria University of WellingtonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1280232019-11-28T16:28:36Z2019-11-28T16:28:36ZAmazon fires are causing glaciers in the Andes to melt even faster<figure><img src="https://images.theconversation.com/files/304292/original/file-20191128-178089-1dwq01a.jpg?ixlib=rb-1.1.0&rect=12%2C31%2C4236%2C2790&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">3523studio / shutterstock</span></span></figcaption></figure><p>If you have turned on a TV or read the news during the past few months, you have probably heard of the widespread fires that wrought havoc on the Amazon rainforest this year. Fires occur in the rainforest every year, but the past 11 months saw the number of fires <a href="http://queimadas.dgi.inpe.br/queimadas/portal-static/situacao-atual/">increase by more than 70%</a> when compared with 2018, indicating a major acceleration in land clearing by the country’s logging and farming industries. </p>
<p>The smoke from the fires rose high into the atmosphere and could be seen from space. Some regions of Brazil became covered in thick smoke that closed airports and <a href="https://www.nationalgeographic.co.uk/environment-and-conservation/2019/08/near-Amazon-fires-residents-are-sick-worried-and-angry">darkened city skies</a>.</p>
<p>As the rainforest burns, it releases enormous amounts of carbon dioxide, carbon monoxide, and larger particles of so-called “black carbon” (<a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008RG000280">smoke and soot</a>). The phrase “enormous amounts” hardly does the numbers justice – in any given year, the burning of forests and grasslands in South America emits a whopping <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/jgrd.50171">800,000 tonnes of black carbon</a> into the atmosphere. </p>
<p>This truly astounding amount is almost double the black carbon produced by all combined energy use in Europe over 12 months. Not only does this absurd amount of smoke cause <a href="https://www.sciencedirect.com/science/article/pii/S0160412005002461">health issues</a> and contribute to <a href="https://www.nature.com/articles/ngeo156">global warming</a> but, as a growing number of scientific studies are showing, it also more directly contributes to the melting of glaciers.</p>
<p>In a new paper published in the journal <a href="https://www.nature.com/articles/s41598-019-53284-1">Scientific Reports</a>, a team of researchers has outlined how smoke from fires in the Amazon in 2010 made glaciers in the Andes melt more quickly. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/304283/original/file-20191128-178078-1lkj9zw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/304283/original/file-20191128-178078-1lkj9zw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/304283/original/file-20191128-178078-1lkj9zw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/304283/original/file-20191128-178078-1lkj9zw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/304283/original/file-20191128-178078-1lkj9zw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/304283/original/file-20191128-178078-1lkj9zw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/304283/original/file-20191128-178078-1lkj9zw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/304283/original/file-20191128-178078-1lkj9zw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">South America: the Andes mountains run along the western edge of the Amazon basin (centre).</span>
<span class="attribution"><span class="source">AridOcean / shutterstock</span></span>
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<p>When fires in the Amazon emit black carbon during the peak burning season (August to October), winds carry these clouds of smoke to Andean glaciers, which can sit higher than 5,000 metres above sea level. </p>
<p>Despite being invisible to the naked eye, black carbon particles affect the ability of the snow to reflect incoming sunlight, a phenomenon known as “albedo”. Similar to how a dark-coloured car will heat up more quickly in direct sunlight when compared with a light-coloured one, glaciers covered by black carbon particles will absorb more heat, and thus melt faster.</p>
<p>By using a computer simulation of how particles move through the atmosphere, known as <a href="https://journals.ametsoc.org/doi/full/10.1175/BAMS-D-14-00110.1">HYSPLIT</a>, the team was able to show that smoke plumes from the Amazon are carried by winds to the Andes, where they fall as an invisible mist across glaciers. Altogether, they found that fires in the Amazon in 2010 caused a 4.5% increase in water runoff from Zongo Glacier in Bolivia.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/304295/original/file-20191128-178066-1uultlb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/304295/original/file-20191128-178066-1uultlb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/304295/original/file-20191128-178066-1uultlb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/304295/original/file-20191128-178066-1uultlb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/304295/original/file-20191128-178066-1uultlb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/304295/original/file-20191128-178066-1uultlb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/304295/original/file-20191128-178066-1uultlb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/304295/original/file-20191128-178066-1uultlb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The Zongo glacier is found on the slopes of Huayna Potosi, one of Bolivia’s highest mountains.</span>
<span class="attribution"><span class="source">Ryan Michael Wilson / shutterstock</span></span>
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<p>Crucially, the authors also found that the effect of black carbon depends on the amount of dust covering a glacier – if the amount of dust is higher, then the glacier will already be absorbing most of the heat that might have been absorbed by the black carbon. Land clearing is one of the reasons that dust levels over South America <a href="https://www.pnas.org/content/104/14/5743.short">doubled</a> during the 20th century.</p>
<p>Glaciers are some of the most important natural resources on the planet. Himalayan glaciers provide drinking water for 240m people, and <a href="https://link.springer.com/book/10.1007%2F978-3-319-92288-1">1.9 billion rely on them for food</a>. In South America, glaciers are crucial for water supply – in some towns, including Huaraz in Peru, <a href="https://unesdoc.unesco.org/ark:/48223/pf0000265810">more than 85% of drinking water comes from glaciers during times of drought</a>. However, these truly vital sources of water are increasingly under threat as the planet feels the effects of global warming. Glaciers in the Andes have been <a href="https://www.the-cryosphere.net/7/81/2013/">receding</a> rapidly for the last 50 years.</p>
<p>The tropical belt of South America is predicted to become <a href="https://www.atmos-chem-phys.net/14/13337/2014/acp-14-13337-2014.html">more dry and arid</a> as the climate changes. A drier climate means more dust, and <a href="https://www.sciencedaily.com/releases/2019/09/190910154657.htm">more fires</a>. It also means more droughts, which make towns more reliant on glaciers for water. </p>
<p>Unfortunately, as the above study shows, the fires assisted by dry conditions help to make these vital sources of water vanish more quickly. The role of black carbon in glacier melting is an exceedingly complex process – currently, the climate models used to <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014WR016728">predict the future melting of glaciers in the Andes</a> do not incorporate black carbon. As the authors of this new study show, this is likely causing the rate of glacial melt to be underestimated in many current assessments. </p>
<p>With communities reliant on glaciers for water, and these same glaciers likely to melt faster as the climate warms, work examining complex forces like black carbon and albedo changes is needed more now than ever before. </p>
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<img alt="" src="https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=140&fit=crop&dpr=1 600w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=140&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=140&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=176&fit=crop&dpr=1 754w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=176&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=176&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/imagine-newsletter-researchers-think-of-a-world-with-climate-action-113443?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=Imagineheader1128023">Click here to subscribe to our climate action newsletter. Climate change is inevitable. Our response to it isn’t.</a></em></p><img src="https://counter.theconversation.com/content/128023/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Harris does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>‘Black carbon’ from rainforest fires is settling on glaciers and making them melt faster, according to new research.Matthew Harris, PhD Researcher, Climate Science, Keele UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1271942019-11-19T08:11:21Z2019-11-19T08:11:21ZFreshwater lakes already emit a quarter of global carbon – and climate change could double that<figure><img src="https://images.theconversation.com/files/302214/original/file-20191118-66979-1ca3kkd.jpg?ixlib=rb-1.1.0&rect=2545%2C0%2C12481%2C7232&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A lake in Banff National Park, Alberta, Canada.</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/Yk6DfYbMDIA">Sergey Pesterev/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Lakes and ponds are the final resting place for many of the Earth’s plants. Rivers collect much of the planet’s dead organic matter, transporting it to rest in calmer waters.</p>
<p>But on a microscopic scale, lakes are anything but calm. An invisible metropolis of microbes feeds on these logs and leaves, producing greenhouse gases as a byproduct.</p>
<p>As a result, lakes may be responsible for as much as a quarter of the carbon in the atmosphere – and rising. <a href="https://doi.org/10.1073/pnas.1904896116">New research</a> conducted with my colleagues in Cambridge, Germany and Canada suggests that emissions from freshwater lakes could double in the coming decades because of climate change.</p>
<p>All known life on Earth is made of carbon. When plants and animals reach the end of their lives, microorganisms such as bacteria and fungi come to feast. They feed on the carbon-based remains of other organisms and their waste products — collectively known as organic matter.</p>
<p>As a byproduct of this never-ending feast, microbes release gases such as carbon dioxide and methane into the environment. While each individual microbe releases a minuscule amount of gas, they are the most abundant organisms on Earth, so it adds up. Energy from sunlight can also break the chemical bonds between molecules of organic matter, releasing smaller molecules, such as carbon dioxide, into the environment.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/302220/original/file-20191118-66932-18tyzwc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/302220/original/file-20191118-66932-18tyzwc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/302220/original/file-20191118-66932-18tyzwc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/302220/original/file-20191118-66932-18tyzwc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/302220/original/file-20191118-66932-18tyzwc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/302220/original/file-20191118-66932-18tyzwc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/302220/original/file-20191118-66932-18tyzwc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Lakes and land are not isolated systems.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/4_5HELfe-Zo">Aaron Burden/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
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<p>Some of this degradation happens on the forest floor. But much of the organic matter that falls to the ground ends up in the water. Winds, rain and snow transport it into lakes, or more often into the rivers that feed them.</p>
<p>The amount of greenhouse gases released from lakes by microbes and sunlight is huge. Initial estimates were <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter06_FINAL.pdf">about 9%</a> of the net carbon released from the Earth’s surface to the atmosphere – that is, the amount released over and above the Earth’s carbon-storing processes.</p>
<p>But, thanks to improved measurements, recent research has revised the figure to <a href="https://doi.org/10.1002/lol2.10055">as high as 25%</a>. These numbers are substantial given that that lakes only comprise about <a href="https://doi.org/10.1002/2014GL060641">4% of the global land surface</a>.</p>
<p>In the coming years, lakes will receive more and more organic matter for microbes to digest. A warming climate will bring <a href="https://doi.org/10.1038/nclimate3004">more forest cover</a> around lakes and a <a href="https://doi.org/10.1890/ES14-00111.1">greater proportion</a> of broad-leaved trees, such as maples and oaks, as compared to needle-leaved trees, such as pines.</p>
<h2>Carbon in a thousand forms</h2>
<p>To understand how changes to forests will alter the role that lakes play in the carbon cycle, we performed an experiment in two Canadian lakes.</p>
<p>We filled plastic containers with rocks, sand, clay and different amounts and types of organic matter from nearby forests. This was intended to mimic the change in forest cover and composition expected from climate change.</p>
<p>We then submerged the containers in shallow lake waters where organic matter is most likely to accumulate and monitored them for three years.</p>
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<p>Using new techniques to analyse the carbon chemistry of water, <a href="https://doi.org/10.1073/pnas.1904896116">we found</a> that those containers simulating a level of forest growth expected in the next few decades led to between 1.5 and 2.7 times more greenhouse gases in the water than conditions simulating today’s forest conditions.</p>
<p>The invisible diversity of organic compounds in the water was the most important factor causing this rise – even more important than the diversity of microbes and the overall amount of organic matter.</p>
<p>The likely explanation for this result is that the same microbes can feed on many different types of molecule. So as the number of carbon-based compounds in the water increases, there are more ways for microbes to feed and release greenhouse gases.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/302219/original/file-20191118-66973-1dp22lq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/302219/original/file-20191118-66973-1dp22lq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/302219/original/file-20191118-66973-1dp22lq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/302219/original/file-20191118-66973-1dp22lq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/302219/original/file-20191118-66973-1dp22lq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/302219/original/file-20191118-66973-1dp22lq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/302219/original/file-20191118-66973-1dp22lq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">They’ll find their way to a lake sooner or later.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/4_5HELfe-Zo">Aaron Burden/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<p>The increase in diversity of organic matter alone was enough to raise greenhouse gas concentrations by about 50%. But the size of this effect nearly doubled in containers with darker overlying waters – <a href="https://link.springer.com/article/10.1007/s10584-015-1514-z">a scenario expected in most lakes</a> as climate change brings increased tree cover.</p>
<p>Accurately tracing how carbon makes its journey from land to atmosphere is vital to predict the pace of climate change and mitigate its effects. By better understanding how the vegetation around lakes controls greenhouse gas concentrations in waters, our research can inform whether changing the way we manage land near lakes could help reduce carbon emissions.</p>
<p>For example, we might want to plant fewer aquatic plants such as cattails in lakeside areas, because they produce <a href="https://doi.org/10.1038/s41467-018-04236-2">much higher</a> concentrations of greenhouse gases than organic matter from forests.</p>
<p>Work also remains to understand fully the role lakes play in the carbon cycle. Not all organic matter that reaches lakes is digested by microbes. Some sinks to the lake floor to form muddy sediment, locking away carbon. The amount of sediment formed will also increase with climate change, but we don’t yet know by how much – and so to what degree this increase in stored carbon will offset the increased greenhouse gas emissions from lakes.</p>
<p>Answering this question will be crucial in improving the accuracy of carbon accounts – and assessing how much time humanity has to balance them.</p>
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<p><em><a href="https://theconversation.com/imagine-newsletter-researchers-think-of-a-world-with-climate-action-113443?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=Imagineheader1127194">Click here to subscribe to our climate action newsletter. Climate change is inevitable. Our response to it isn’t.</a></em></p><img src="https://counter.theconversation.com/content/127194/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew J Tanentzap receives funding for climate change research from the Natural Environment Research Council, European Research Council, and Royal Society.</span></em></p>Lakes are the final resting place for many of the Earth’s plants – and these organic graveyards are about to get a whole lot busier.Andrew J Tanentzap, Reader in Global Change Ecology, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1266712019-11-12T19:02:47Z2019-11-12T19:02:47ZClimate explained: how growth in population and consumption drives planetary change<figure><img src="https://images.theconversation.com/files/301157/original/file-20191111-178525-ht8l9a.jpg?ixlib=rb-1.1.0&rect=98%2C117%2C4263%2C2785&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Rapid population growth and increased consumption are now seen as the main drivers of environmental changes.</span> <span class="attribution"><span class="source">from www.shutterstock.com</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><strong><a href="https://theconversation.com/nz/topics/climate-explained-74664">Climate Explained</a></strong> is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.</em> </p>
<p><em>If you have a question you’d like an expert to answer, please send it to climate.change@stuff.co.nz</em></p>
<blockquote>
<p><strong>The growth of the human population over the last 70 years has exploded from 2 billion to nearly 8 billion, with a compounding net growth of over 30,000 per day. We all breathe out carbon dioxide with every breath. That equates to about 140 billion CO₂ breaths every minute. Isn’t it logical that atmospheric carbon will continue to increase with the birth rate regardless of what we do about fossil fuel reduction?</strong></p>
</blockquote>
<p>This question touches on the core of our impact on planetary change. It highlights the exponential growth in the human population, but also homes in on the potential direct input of carbon dioxide from humans, through respiration. </p>
<p>As I explain in more detail below, our breathing does not contribute to the net accumulation of carbon dioxide in the atmosphere. But population growth, combined with an increase in consumption, is now seen as the <a href="https://www.stockholmresilience.org/research/research-news/2015-01-15-new-planetary-dashboard-shows-increasing-human-impact.html">main driver of change in the Earth system</a>. </p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/climate-explained-why-your-backyard-lawn-doesnt-help-reduce-carbon-dioxide-in-the-atmosphere-122312">Climate explained: why your backyard lawn doesn't help reduce carbon dioxide in the atmosphere</a>
</strong>
</em>
</p>
<hr>
<h2>Humans: a moment in geological time</h2>
<p>Earth has been around for 4.56 billion years. The <a href="https://www.livescience.com/1804-greatest-mysteries-life-arise-earth.html">earliest evidence for life on Earth</a> comes from fossilised mats of cyanobacteria that are about 3.7 billion years old. </p>
<p>From around 700 million years ago, and certainly from 540 million years ago, life exploded into its present myriad forms, from molluscs to lung fish, reptiles, insects, plants, fishes and mammals – culminating in hominids and finally <em>Homo sapiens</em>. Genetic studies suggest <a href="https://www.nature.com/scitable/knowledge/library/overview-of-hominin-evolution-89010983/">hominids evolved from primates around 6 million years ago</a>, with the oldest hominid fossil dating from 4.4 million years ago in East Africa. </p>
<p>Our species appeared around 200,000 to 300,000 years ago, a blink of an eye in geological terms. From Africa, <em>Homo sapiens</em> migrated through Europe and Asia and spread across the world, at lightning speeds. </p>
<p>Part of the question is about a putative link between human biological functions and climate. <em>Homo sapiens</em> is <a href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001127">one of more than 28 million living species today</a>, and some <a href="https://link.springer.com/chapter/10.1007/978-94-011-5874-9_7">35 billion species that have ever lived on Earth</a>. There has always been a link between life and Earth’s atmosphere, and perhaps the clearest indicator is oxygen. </p>
<h2>Life, carbon and climate</h2>
<p>Cyanobacteria were the first organisms to master photosynthesis and <a href="https://www.pnas.org/content/96/20/10955">began adding oxygen to Earth’s early atmosphere</a>, producing levels of 2% by 1 billion years ago. Today oxygen levels are at 20%. </p>
<p>While people inhale oxygen and exhale carbon dioxide (billions of tonnes each year), this does <a href="https://slate.com/news-and-politics/2009/08/are-you-heating-the-planet-when-you-breathe.html">not represent new carbon in the atmosphere</a>, but rather recycled carbon that had been taken up by the animals and plants we eat. Furthermore, the hard parts of human skeletons are potential carbon stores, if buried sufficiently deep. </p>
<p>There is a constant cycling of carbon between geological, oceanographic and biological processes. <em>Homo sapiens</em> is part of this carbon cycle that plays out at the Earth’s surface. Like all living organisms, we derive the carbon we need from our immediate environment and give it up again through breathing, living and dying. </p>
<p>Carbon is only added to the atmosphere if it is taken out of long-term geological stores such as carbon-rich sediments, oil, natural gas and coal.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/climate-explained-why-carbon-dioxide-has-such-outsized-influence-on-earths-climate-123064">Climate explained: why carbon dioxide has such outsized influence on Earth's climate</a>
</strong>
</em>
</p>
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<h2>Planetary impact of humans</h2>
<p>But the <a href="https://ourworldindata.org/world-population-growth">remarkable growth in human population</a> is surely the critical issue. Ten thousand years ago, there were 1 million people on Earth. By 1800, there were 1 billion, 3 billion by 1960 and almost 8 billion today.</p>
<p>When these figures are plotted on a graph, the growth line looks almost vertical from the 1800s onwards. <a href="https://www.pewresearch.org/fact-tank/2019/06/17/worlds-population-is-projected-to-nearly-stop-growing-by-the-end-of-the-century/">Population growth may eventually flatten out</a>, but only at around 10-11 billion. </p>
<p>Alongside the unprecedented population growth of humans has been the <a href="https://www.ipbes.net/news/million-threatened-species-thirteen-questions-answers">loss of many non-human species</a> (10,000 extinctions per million populations per year, or <a href="https://www.theguardian.com/environment/2018/oct/30/humanity-wiped-out-animals-since-1970-major-report-finds">60% of animal populations since 1970</a>), the rapid loss of wilderness habitat and consequent growth in farmed land, over-fishing (with up to <a href="http://blogs.edf.org/edfish/2012/07/11/fao-reports-87-of-the-worlds-fisheries-are-overexploited-or-fully-exploited/">87% of fisheries fully exploited</a>), and a staggering growth in global car numbers (from zero in the 1920s to 1 billion in 2013 and a projected <a href="https://www.weforum.org/agenda/2016/04/the-number-of-cars-worldwide-is-set-to-double-by-2040">2 billion by 2040</a>).</p>
<p>The <a href="https://www.usgs.gov/centers/nmic/copper-statistics-and-information">world production of copper</a> is an instructive proxy for human global impacts. As with many commodity curves, the trend from 1900, and particularly from the 1950s, is exponential. In 1900 around half-a-million tonnes of copper was produced worldwide. Today it is 18 million tonnes per year, with no sign of lowering consumption rates. Copper is the feedstock for much of modern-day and future green technologies. </p>
<p>Most parts of the world now experience material consumption as never before. But serious inequality remains, with over <a href="https://www.worldbank.org/en/news/press-release/2018/10/17/nearly-half-the-world-lives-on-less-than-550-a-day">3 billion living on less than US$5.50 a day</a>, and a <a href="https://www.oxfam.org/en/press-releases/just-8-men-own-same-wealth-half-world">tiny percentage who own so much</a>. </p>
<p>Some argue that it is not the numbers of people on Earth that count, but rather the way we consume and share. Whatever the politics and economics, the gross consumption level of billions of humans is, surely, the main cause of planetary change, especially since 1950. Present-day atmospheric levels of carbon dioxide are one of many symptoms of human impact.</p><img src="https://counter.theconversation.com/content/126671/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Petterson has received funding for research and international development programmes during his career.</span></em></p>Discussions about climate change often skirt around the issue of population growth, but it is the main driver of rising carbon dioxide levels and many other environmental changes on a planetary scale.Michael Petterson, Professor of Geology, Auckland University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1135182019-05-09T10:37:37Z2019-05-09T10:37:37ZDeep sea carbon reservoirs once superheated the Earth – could it happen again?<figure><img src="https://images.theconversation.com/files/273412/original/file-20190508-183077-p58kfz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Droplets rising from the Champagne vent on the ocean floor in the Mariana Islands. Fluids venting from the site contain dissolved carbon dioxide. </span> <span class="attribution"><a class="source" href="https://oceanexplorer.noaa.gov/explorations/04fire/logs/april10/media/bubbles.html">NOAA Ocean Explorer</a></span></figcaption></figure><p>As concern grows over human-induced climate change, many scientists are looking back through Earth’s history to events that can shed light on changes occurring today. Analyzing how the planet’s climate system has changed in the past improves our understanding of how it may behave in the future.</p>
<p>It is now clear from these studies that abrupt warming events are <a href="https://www.britannica.com/science/climate-change/Abrupt-climate-changes-in-Earth-history">built into Earth’s climate system</a>. They have occurred when disturbances in carbon storage at Earth’s surface released greenhouse gases into the atmosphere. One of the grand challenges for <a href="https://scholar.google.com/citations?user=0-0jvDwAAAAJ&hl=en">climate scientists like me</a> is to determine where these releases came from before humans were present, and what triggered them. Importantly, we want to know if such an event could happen again.</p>
<p>In a recently published study, my colleagues <a href="http://rses.anu.edu.au/people/katie-harazin">Katie Harazin</a>, <a href="https://portal.research.lu.se/portal/en/persons/nadine-b-quintana-krupinski(3cc6c619-0e19-492f-b33b-94ca161bebf7).html">Nadine Krupinski</a> and I discovered that at the end of the last glacial era, about 20,000 years ago, carbon dioxide was <a href="https://doi.org/10.1088/1748-9326/aafe28">released into the ocean from geologic reservoirs</a> located on the seafloor when the oceans began to warm. </p>
<p>This finding is a potential game-changer. Naturally occurring reservoirs of carbon in the modern ocean could be disturbed again, with potentially serious effects to Earth’s oceans and climate.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273388/original/file-20190508-183109-wr9bpt.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273388/original/file-20190508-183109-wr9bpt.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273388/original/file-20190508-183109-wr9bpt.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=202&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273388/original/file-20190508-183109-wr9bpt.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=202&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273388/original/file-20190508-183109-wr9bpt.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=202&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273388/original/file-20190508-183109-wr9bpt.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=253&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273388/original/file-20190508-183109-wr9bpt.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=253&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273388/original/file-20190508-183109-wr9bpt.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=253&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Earth has cycled between ice ages (low points) and warm interglacial periods over the past 800,000 years. But current climatic warming is occurring much faster than past warming events.</span>
<span class="attribution"><a class="source" href="https://earthobservatory.nasa.gov/features/GlobalWarming/page3.php">NASA</a></span>
</figcaption>
</figure>
<h2>The past is prologue</h2>
<p>One of the best-known examples of a rapid warming caused by release of geologic carbon is the <a href="https://doi.org/10.1038/353225a0">Paleocene-Eocene Thermal Maximum</a>, or PETM, a major global warming event that occured about 55 million years ago. During the PETM, the Earth warmed by 9 to 16 degrees Fahrenheit (5 to 9 degrees Celsius) within about 10,000 years. </p>
<p>Climate scientists now consider the PETM to be an <a href="https://doi.org/10.1038/ngeo2681">analog for environmental changes taking place today</a>. The PETM happened over a longer period and without human involvement, but it shows that there is inherent instability in the climate system if carbon from geologic reservoirs is released rapidly. </p>
<p>Scientists also know that atmospheric carbon dioxide levels rose rapidly at the end of <a href="https://commons.wikimedia.org/wiki/File:Atmospheric_CO2_with_glaciers_cycles.png">each of the late Pleistocene ice ages</a>, helping to warm the climate. During the most recent warming episode, 17,000 years ago, the Earth warmed by 9 to 13 degrees Fahrenheit (5 to 7 degrees Celsius).</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ldLBoErAhz4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The Paleocene-Eocene Thermal Maximum warmed the planet so dramatically that tropical rain forests extended northward to the Arctic.</span></figcaption>
</figure>
<p>However, hundreds of scientific studies have failed to establish what caused the rapid carbon dioxide increases that ended each ice age. Researchers agree that the ocean must be involved because it acts as a large carbon capacitor, <a href="https://interactiveoceans.washington.edu/story/Carbon_Cycle">regulating the amount of carbon that resides in the atmosphere</a>. But they are still searching for clues to understand what influences the amount of carbon in the ocean during abrupt climate changes.</p>
<h2>Lakes on the ocean floor</h2>
<p>Over the past two decades, ocean scientists have discovered that there are reservoirs of liquid and solid carbon dioxide accumulating at the bottom of the ocean, within the rocks and sediments on the margins of active <a href="https://oceanservice.noaa.gov/facts/vents.html">hydrothermal vents</a>. At these sites, volcanic magma from within the Earth meets superheated water, producing plumes of carbon dioxide-rich fluids that filter through crevices in the Earth’s crust, migrating upward towards the surface.</p>
<p>When a plume of this fluid meets cold seawater, the carbon dioxide can solidify into a form called hydrate. The hydrate forms a cap that traps carbon dioxide within the rocks and sediments and keeps it from entering the ocean. But at temperatures above roughly 48 degrees Fahrenheit (9 degrees Celsius), hydrate will melt, releasing buoyant liquid or gaseous carbon dioxide directly into the overlying water. </p>
<p>Scientists have thus far documented reservoirs of liquid and hydrate carbon dioxide in the western Pacific near Taiwan and in the <a href="https://www.whoi.edu/news-release/co2-pools">Aegean Sea</a>. In shallower waters, where ocean temperatures are warmer and pressure is lower, researchers have observed pure carbon dioxide <a href="https://phys.org/news/2018-02-carbon-dioxide-leakage-seabed.html">emanating directly from sediments as a gas</a> and rising to the ocean’s surface.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273377/original/file-20190508-183106-1iccetn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273377/original/file-20190508-183106-1iccetn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273377/original/file-20190508-183106-1iccetn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=377&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273377/original/file-20190508-183106-1iccetn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=377&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273377/original/file-20190508-183106-1iccetn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=377&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273377/original/file-20190508-183106-1iccetn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=474&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273377/original/file-20190508-183106-1iccetn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=474&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273377/original/file-20190508-183106-1iccetn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=474&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Nearly pure carbon dioxide bubbles rise from sediments that blanket an active hydrothermal system in the western tropical Pacific.</span>
<span class="attribution"><a class="source" href="https://iopscience.iop.org/article/10.1088/1748-9326/aafe28">Photos by Roy Price, courtesy of Jan Amend</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>A climate wild card</h2>
<p>These discoveries are changing scientists’ understanding of the marine carbon system. Climate scientists have not included deep sea carbon reservoirs in current models that explore the potential impacts of future warming, because little is known about the size and distribution of these carbon sources. </p>
<p>In fact, there is virtually no data that documents how much carbon dioxide is currently being released from these reservoirs into the ocean. This makes the geologic history critically important: It confirms that these types of reservoirs have the capacity to release vast amounts of carbon when they are disturbed.</p>
<p>Analogous carbon reservoirs have also been identified in terrestrial environments. In 1979, Indonesia’s Dieng volcano <a href="https://doi.org/10.1016/0377-0273(89)90058-9">suffocated 142 people</a> when it released nearly pure carbon dioxide. In 1986, a carbon dioxide reservoir at the bottom of Lake Nyos in Cameroon <a href="http://volcano.oregonstate.edu/silent-deadly">erupted</a>, killing 1,700 local villagers and hundreds of animals. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/273385/original/file-20190508-183109-ijlwoy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273385/original/file-20190508-183109-ijlwoy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/273385/original/file-20190508-183109-ijlwoy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=902&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273385/original/file-20190508-183109-ijlwoy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=902&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273385/original/file-20190508-183109-ijlwoy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=902&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273385/original/file-20190508-183109-ijlwoy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1134&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273385/original/file-20190508-183109-ijlwoy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1134&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273385/original/file-20190508-183109-ijlwoy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1134&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Cow suffocated by carbon dioxide in the 1986 Lake Nyos eruption.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Lake_Nyos_disaster#/media/File:Cow_killed_by_Lake_Nyos_gasses.jpg">USGS/Jack Lockwood</a></span>
</figcaption>
</figure>
<p>Carbon dioxide is also venting around Mammoth Mountain, California, at spots where magma rises through Earth’s crust and stalls at shallow depths. High concentrations of carbon dioxide in the soil have <a href="https://volcanoes.usgs.gov/volcanoes/long_valley/field_guides_horseshoe_lake.html">killed more than 100 acres of trees</a>. Scientists are working to identify and characterize <a href="https://www.smithsonianmag.com/science-nature/defusing-africas-killer-lakes-88765263/">other sites on land</a> where such releases could occur.</p>
<p>It is much more challenging to quantify the carbon dioxide stored in ocean reservoirs. Vast regions of the seafloor contain sites of active volcanism and hydrothermal venting, but scientists know virtually nothing about how much carbon dioxide is accumulating in surrounding rocks and sediments. In my view, there is an urgent need to study marine settings where carbon dioxide is likely accumulating, and then to assess how susceptible they may be to destabilization. </p>
<h2>Warming oceans, increasing risk</h2>
<p>This is not an endeavor that should be deferred. Earth’s oceans are warming rapidly, and climate models project that they will warm fastest near the poles, where deep currents form that <a href="https://oceanservice.noaa.gov/facts/conveyor.html">carry warming waters downward from the surface</a>. </p>
<p>As these warm waters sink into the ocean’s interior, they transport excess heat towards sites where carbon dioxide reservoirs can form. Those warmer waters will eventually destabilize the hydrate seals that keep liquid carbon dioxide trapped.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273379/original/file-20190508-183080-bnph48.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273379/original/file-20190508-183080-bnph48.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273379/original/file-20190508-183080-bnph48.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=358&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273379/original/file-20190508-183080-bnph48.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=358&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273379/original/file-20190508-183080-bnph48.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=358&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273379/original/file-20190508-183080-bnph48.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=450&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273379/original/file-20190508-183080-bnph48.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=450&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273379/original/file-20190508-183080-bnph48.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=450&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A very large, slow current called the thermohaline circulation carries warm water to Earth’s polar regions, where it cools and sinks to the deep oceans.</span>
<span class="attribution"><a class="source" href="http://www.grida.no/resources/6918">Maphoto/Riccardo Pravettoni via GRID-Arendal</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>One such reservoir occurs in the western Pacific west of the <a href="https://en.wikipedia.org/wiki/Okinawa_Trough">Okinawa Trough</a> in the East China Sea. The temperature of the bottom waters at this location is 37 to 39 degrees Fahrenheit (3 to 4 degrees Celsius), which means the hydrate cap is within about 4-5 degrees Celsius of its melting point. </p>
<p>Importantly, warm hydrothermal fluids are rising from below the carbon dioxide reservoir toward the surface. As the oceans continue to warm, the temperature difference between cold ocean waters and warmer hydrothermal fluids will decrease. This will cause the hydrate to thin, potentially to a point where it will no longer keep liquid carbon dioxide from escaping.</p>
<p>To date there has been no research to assess whether these ocean carbon dioxide reservoirs are vulnerable to rising ocean temperatures. But Earth’s pre-historic record clearly demonstrates that geologic reservoirs can be destabilized – and that when they are, it leads to rapid increases in atmospheric carbon dioxide and global warming. In my view, this represents an important unknown risk that cannot be ignored.</p><img src="https://counter.theconversation.com/content/113518/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lowell D. Stott receives funding from the National Science Foundation. </span></em></p>Thousands of years ago, carbon gases trapped on the seafloor escaped, causing drastic warming that helped end the last ice age. A scientist says climate change could cause this process to repeat.Lowell D. Stott, Professor, USC Dornsife College of Letters, Arts and SciencesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1055242018-10-30T14:11:23Z2018-10-30T14:11:23ZWe desperately need to store more carbon – seagrass could be the answer<figure><img src="https://images.theconversation.com/files/242457/original/file-20181026-7065-1a6tzvv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">shutterstock</span> </figcaption></figure><p>According to the UN’s Intergovernmental Panel on Climate Change, urgent and unprecedented changes are needed to avoid a <a href="http://www.ipcc.ch/report/sr15/">climate change catastrophe</a>. Although efforts are already being made to reduce the production of greenhouse gasses, they are by most estimations not enough. </p>
<p>It is therefore critical that we find ways to drastically reduce the amount of pollutants in the atmosphere. Ecosystems capable of absorbing and storing large amounts of carbon dioxide know as “carbon sinks” are ideal for this. </p>
<p>In principle, all living organisms – all animals, plants, algae and bacteria – consist of carbon and so function as a carbon sink. For example, as long as a tree lives it will absorb and store carbon. Given the sheer volume of all the trees contained in tropical forests, it’s no wonder most people imagine such forests when they think of a carbon sink.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/242732/original/file-20181029-76416-18dai1a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/242732/original/file-20181029-76416-18dai1a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/242732/original/file-20181029-76416-18dai1a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=896&fit=crop&dpr=1 600w, https://images.theconversation.com/files/242732/original/file-20181029-76416-18dai1a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=896&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/242732/original/file-20181029-76416-18dai1a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=896&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/242732/original/file-20181029-76416-18dai1a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1125&fit=crop&dpr=1 754w, https://images.theconversation.com/files/242732/original/file-20181029-76416-18dai1a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1125&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/242732/original/file-20181029-76416-18dai1a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1125&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Stores lots of carbon – but mostly above ground.</span>
<span class="attribution"><span class="source">Hugh Lansdown/Shutterstock</span></span>
</figcaption>
</figure>
<p>However, once chopped down and turned into firewood, the carbon in those trees will be released and emitted back into the atmosphere as CO₂. So while a forest is a moderately efficient carbon sink, its capacity to retain carbon in the forest floor is limited. </p>
<p>In fact, new research by colleagues and I has found that such forests are actually only the <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GB005941">fifth most efficient ecosystem</a> in the carbon storage cycle behind salt marshes, mangrove forests, seagrass meadows and, best of all, tundra.</p>
<p>Tundra is found in polar or mountainous regions where temperatures are too low for trees to grow, and the landscape is dominated by grasses or moss. As a large part of the carbon is stored in the frozen soil and so is harder to disturb, it makes a very efficient sink. However, rising temperatures are <a href="https://www.scientificamerican.com/article/melting-tundra-releases-carbon-dioxide-quickly/">melting the tundra</a> in many parts of the world, releasing stored carbon back into the atmosphere, and as a consequence its capacity to store carbon is decreasing. </p>
<p>While forests and tundras are losing capacity for carbon storage, another often forgotten ecosystem may hold the answer: seagrass. </p>
<h2>We need to create vast underwater meadows</h2>
<p>Seagrass plants have an excellent capacity for taking up and storing carbon in the oxygen-depleted seabed, where it decomposes much slower than on land. This oxygen-free sediment traps the carbon in the dead plant material which may then remain buried for hundreds of years. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/242979/original/file-20181030-76384-e4m1ir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/242979/original/file-20181030-76384-e4m1ir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/242979/original/file-20181030-76384-e4m1ir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=433&fit=crop&dpr=1 600w, https://images.theconversation.com/files/242979/original/file-20181030-76384-e4m1ir.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=433&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/242979/original/file-20181030-76384-e4m1ir.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=433&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/242979/original/file-20181030-76384-e4m1ir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=545&fit=crop&dpr=1 754w, https://images.theconversation.com/files/242979/original/file-20181030-76384-e4m1ir.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=545&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/242979/original/file-20181030-76384-e4m1ir.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=545&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Seagrass can grow at depths of up to 90m and is an important part of the food web.</span>
<span class="attribution"><span class="source">Anita Kainrath / shutterstock</span></span>
</figcaption>
</figure>
<p>Seagrass meadows are, for the most part, in recession across the globe due to human activity. As a result the re-establishment of these meadows will make it possible to <a href="http://www.climateaction.org/news/seagrass_vital_carbon_sink_in_solution_to_climate_change">greatly increase</a> the carbon storage potential of our oceans.</p>
<p>Many factors influence the exact amount of carbon that can be taken up by a seagrass meadow, but rough calculations show that if we restore one hectare of seagrass, it would correspond to at least ten hectares of dry-land forest and even <a href="https://www.abc.net.au/news/science/2018-03-26/blue-carbon-mangroves-seagrass-fight-climate-change/9564096">as much as 40</a>.</p>
<p>Planting vast areas of seagrass meadow is also an eminently doable task as these plants are not seaweeds, but plants with flowers, leaves and roots just like plants on land. This means they produce seeds that can be sown in the seabed or small shoots that can be planted by divers. To develop new techniques for actually planting all this seagrass on a massive scale, colleagues and I have been involved in the <a href="https://www.novagrass.dk/en">Novagrass project</a>, which trialled seagrass planting in the coastal zone around Denmark.</p>
<p>We tested various techniques, involving both seeds and seedlings, and had the most success when planting seedlings in chequerboard patterns on the seabed. The lessons from this project are now being applied in a larger scale trial, where muddy seabed is topped up with a layer of sand before seedlings are planted. We are waiting on the results, but so far this technique appears to be a promising way to re-establish eelgrass in coastal areas.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/242726/original/file-20181029-76411-k5irhs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/242726/original/file-20181029-76411-k5irhs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/242726/original/file-20181029-76411-k5irhs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=342&fit=crop&dpr=1 600w, https://images.theconversation.com/files/242726/original/file-20181029-76411-k5irhs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=342&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/242726/original/file-20181029-76411-k5irhs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=342&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/242726/original/file-20181029-76411-k5irhs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=429&fit=crop&dpr=1 754w, https://images.theconversation.com/files/242726/original/file-20181029-76411-k5irhs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=429&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/242726/original/file-20181029-76411-k5irhs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=429&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Marine eelgrasses are found in shallow seas across much of the world.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:World_map_ocean_genus-Zostera.jpg">gerardgiraud/wiki</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>There are about 60 seagrass species in the world to choose from, but we focused on common eelgrass (<em>Zostera marina</em>). It cannot tolerate warm seas but it’s the most common species in temperate areas and grows well around coasts in the northern hemisphere. Seagrasses thrive in coastal zones, they have the potential to grow all over the world (except Antarctica) and are even <a href="https://www.nature.com/articles/s41598-018-32249-w">expanding into the Arctic</a> as the ice recedes. </p>
<p>There is some evidence of <a href="https://www.sciencedirect.com/science/article/pii/S0022098117301417">natural recovery</a> after excessive nutrients from fertilisers and other human pressures have been relieved. But much more action is needed to avoid further loss – and indeed new growth – of these valuable ecosystems.</p><img src="https://counter.theconversation.com/content/105524/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Marianne Holmer receives funding from Villum fonden. </span></em></p>Vast ‘underwater meadows’ would lock up lots of carbon.Marianne Holmer, Professor of Biology, University of Southern DenmarkLicensed as Creative Commons – attribution, no derivatives.