tag:theconversation.com,2011:/au/topics/ice-cores-3664/articlesIce cores – The Conversation2023-04-05T20:03:35Ztag:theconversation.com,2011:article/2031852023-04-05T20:03:35Z2023-04-05T20:03:35Z‘Like blood, then turned into darkness’: how medieval manuscripts link lunar eclipses, volcanoes and climate change<figure><img src="https://images.theconversation.com/files/519148/original/file-20230403-17-t8wel.jpg?ixlib=rb-1.1.0&rect=445%2C222%2C3456%2C2430&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A diagram of a lunar eclipse from De Sphaera Mundi by Johannes de Sacrobosco, c. 1240 AD.</span> <span class="attribution"><a class="source" href="https://digitalcollections.nypl.org/items/148cf2c0-f054-0138-15e1-0242ac110003">New York Public Library</a></span></figcaption></figure><p>Before humans started heating the planet by burning fossil fuels in the 19th century, Earth had experienced centuries-long widespread cool period known as the Little Ice Age.</p>
<p>Scientists believe this cold spell may have been <a href="https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2011GL050168">triggered, in part, by volcanic eruptions</a> which made the atmosphere hazier, blocking some incoming sunlight. </p>
<p>Records of these eruptions are sparse, and much of our knowledge of them comes from the traces left behind in <a href="https://www.nature.com/articles/s41467-019-08357-0">polar ice</a> and <a href="https://www.sciencedirect.com/science/article/abs/pii/S0277379115301888">tree rings</a>, which are fragmentary and sometimes contradictory.</p>
<p>In a <a href="https://www.nature.com/articles/s41586-023-05751-z">new study published in Nature</a>, an international team of researchers led by Sébastien Guillet at the University of Geneva has found another way to learn about these historical eruptions: by studying descriptions of lunar eclipses in medieval manuscripts.</p>
<h2>Dark eclipses</h2>
<p>The researchers compiled hundreds of records of lunar eclipses from across Europe, the Middle East, and Asia, documenting 187 eclipses between 1100 and 1300. </p>
<p>In particular, they searched for descriptions that provided information on the brightness and colour of the Moon during the eclipse. Most of these turned out to be from European monks or clerics, writing in Latin.</p>
<p>Based on these descriptions, the researchers ranked the colour and brightness of the Moon reported in each total eclipse. The brighter the eclipse, the clearer the atmosphere at the time: darker eclipses indicated a higher level of aerosol particles in the upper atmosphere – a marker of recent volcanic activity.</p>
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<img alt="" src="https://images.theconversation.com/files/519473/original/file-20230405-18-65dlb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519473/original/file-20230405-18-65dlb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519473/original/file-20230405-18-65dlb3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519473/original/file-20230405-18-65dlb3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519473/original/file-20230405-18-65dlb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519473/original/file-20230405-18-65dlb3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519473/original/file-20230405-18-65dlb3.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">
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<span class="caption">During a total lunar eclipse, the Moon turns red due to sunlight refracted by Earth’s atmosphere. A particularly dark eclipse indicates more aerosols in the atmosphere, which is a sign of recent volcanic activity.</span>
<span class="attribution"><span class="source">Chris Harwood / Shutterstock</span></span>
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<p>The next step was to put the eclipse data together with simulations of how aerosol particles behave in the atmosphere, modern satellite observations, and climatic evidence from historical tree ring records. </p>
<p>This allowed the researchers to estimate the timing of the culprit eruptions more precisely than from previous ice core records – and determine which eruptions reached the stratosphere and would be more likely to generate climatic cooling effects.</p>
<h2>What lunar eclipses tell us about the state of the atmosphere</h2>
<p>A total lunar eclipse is a beautiful sight. When the Sun, Earth and Moon align perfectly, our planet blocks direct sunlight from reaching the Moon’s surface. </p>
<p>However, Earth’s atmosphere bends sunlight around our planet. As a result, some sunlight reaches the Moon even during a total eclipse. </p>
<p>Earth’s atmosphere also scatters sunlight - acting as a giant colour filter. The bluer the light, the more it is scattered – which is why the sky is blue in the daytime, and why the Sun appears ruddy at dawn and dusk.</p>
<p>During a total lunar eclipse, the sunlight reaching the Moon has been filtered by Earth’s atmosphere, removing much of the blue and yellow light. The light that reaches the Moon is effectively the sum of all the dawns and all the dusks occurring at that time. </p>
<p>And the state of Earth’s atmosphere at that time controls just how much light is filtered. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/mbT50-rppaU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">NASA video released to explain the total Lunar eclipse seen from the Americas in December 2011.</span></figcaption>
</figure>
<h2>How volcanoes affect lunar eclipses</h2>
<p>If you’ve ever seen a sunset during a dust storm, or on a very smoky day, you know the extra particles clogging up the sky can produce deep, vibrant reds and oranges.</p>
<p>Imagine a total lunar eclipse occurring while wildfires rage overseas. The fires would pump smoke and dust into Earth’s atmosphere, making the Moon redder and darker during the eclipse. </p>
<p>Which brings us to the effect of volcanoes. The largest volcanic eruptions pump vast amounts of material into Earth’s stratosphere, where it can remain for many months. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1538151976751755271"}"></div></p>
<p>The spectacular volcanic sunsets seen throughout Australia in the months following the Tongan volcanic eruption of January 2022 are a great example. And that material, once in the stratosphere, will spread around Earth.</p>
<p>What effect does this have on lunar eclipses? It turns out the brightness of the Moon during a lunar eclipse depends the amount of material in our stratosphere. In the months after a large eruption, any lunar eclipse would be markedly darker than normal.</p>
<h2>How volcanoes affect the climate</h2>
<p>Volcanic eruptions can eject huge amounts of ash, sulphur dioxide, and other gases high into the atmosphere. Eruptions can cause either cooling or warming (both temporary). The effect depends on exactly what the volcano spews out, how high the plume reaches, and the volcano’s location.</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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<p>Sulphur dioxide is particularly important. If it reaches the stratosphere, it reacts with water vapour to form a lingering veil of sulphate aerosols. These aerosols, along with the volcanic ash, block and scatter Solar radiation, often leading to cooling at the Earth’s surface.</p>
<p>Large volcanic eruptions, such as the <a href="https://earthobservatory.nasa.gov/images/1510/global-effects-of-mount-pinatubo">1991 Mount Pinatubo eruption</a> in the Philippines and the infamous <a href="https://www.cambridge.org/core/journals/quaternary-research/article/abs/historic-eruptions-of-tambora-1815-krakatau-1883-and-agung-1963-their-stratospheric-aerosols-and-climatic-impact/13CE8FA2B0EF3BE25951FB759F904446">1815 eruption of Tambora</a> in Indonesia, slightly lowered global temperature in the years after the eruption. After Tambora, Europe and North America experienced a “<a href="https://iopscience.iop.org/article/10.1088/1748-9326/ab3a10">year without a summer</a>” in 1816.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/519457/original/file-20230405-22-ay5bt0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo from the International Space Station showing white puffy clouds over the ocean and a dark grey plume from a volcanic eruption." src="https://images.theconversation.com/files/519457/original/file-20230405-22-ay5bt0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519457/original/file-20230405-22-ay5bt0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519457/original/file-20230405-22-ay5bt0.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519457/original/file-20230405-22-ay5bt0.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519457/original/file-20230405-22-ay5bt0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519457/original/file-20230405-22-ay5bt0.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519457/original/file-20230405-22-ay5bt0.jpeg?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 plume of ash and smoke from the 2022 Hunga Tonga-Hunga Ha'apai eruption was visible from the International Space Station.</span>
<span class="attribution"><span class="source">EPA / NASA / Kayla Barron</span></span>
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<p>On the other hand, water vapour and carbon dioxide from volcanic eruptions have a warming effect. It’s only small, as all present-day volcanic emissions produce <a href="https://www.usgs.gov/programs/VHP/volcanoes-can-affect-climate">less than 1%</a> of the carbon dioxide released by human activities. </p>
<h2>The past and future of volcanoes, eclipses, and the climate</h2>
<p>Eyewitness accounts through historical reports and oral traditional knowledge are often overlooked in the study of volcanoes. However, the inclusion of broader sources of knowledge is incredibly valuable to help us understand past impacts of volcanic eruptions on people and the environment.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/when-the-bullin-shrieked-aboriginal-memories-of-volcanic-eruptions-thousands-of-years-ago-81986">When the Bullin shrieked: Aboriginal memories of volcanic eruptions thousands of years ago</a>
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<p>In this study, the combination of historical observations with ice records and climate reconstructions from tree rings has enabled more precise timing of those ancient eruptions. In turn, this has allowed us to better understand their potential impact on the climate during the European Middle Ages. Such information can help us to understand the role these eruptions may have played in the transition to the Little Ice Age.</p>
<p>In the future, volcanoes may have to work a little harder to create a “dark” eclipse. As the atmosphere warms, the altitude of the stratosphere will increase. As a result, it may take a bigger eruption to put significant amounts of aerosols into the upper layer where they will hang around to darken the Moon for future generations!</p><img src="https://counter.theconversation.com/content/203185/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Heather Handley receives funding from the Australian Research Council. She is Co-Founder of Women in Earth and Environmental Sciences Australasia (WOMEESA) and Co-Founder and Director of the Earth Futures Festival.</span></em></p><p class="fine-print"><em><span>Jonti Horner 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>Medieval monks recorded hundreds of lunar eclipses. Centuries later, their descriptions are helping scientists unravel the role of volcanoes in historical climate change.Heather Handley, Associate Professor of Volcanology and Geoscience Communication, University of Twente and Adjunct Associate Professor, Monash UniversityJonti Horner, Professor (Astrophysics), University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1447842020-09-03T12:27:17Z2020-09-03T12:27:17ZVideo: How ancient ice cores show ‘black swan’ events in history – even pandemics<p><em><a href="https://byrd.osu.edu/people/thompson.3">Lonnie Thompson</a> and <a href="https://byrd.osu.edu/people/thompson.4">Ellen Mosley-Thompson</a> at The Ohio State University have been studying ice cores from around the world for over 30 years. They collect, <a href="https://byrd.osu.edu/research/facilities/cold-storage-ice-core">store</a> and study ice cores to understand the history of the Earth’s climate and preserve them for future scientists. In this interview, they explain how <a href="https://youtu.be/ZHOdqb9ViLw">ice cores preserve evidence</a> of rare but impactful changes in Earth’s history often called “black swan” events, as well as smaller environmental changes and why it is necessary to preserve the ice cores and the glaciers they come from.</em></p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/ZHOdqb9ViLw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">What can ice cores tell us about historical black swan events?</span></figcaption>
</figure>
<h2>How do ice cores help in understanding the past?</h2>
<p>Ice cores are columns of ice drilled through glaciers that are highly versatile and detailed recorders of Earth’s climate and environment that cover hundreds to many thousands of years. </p>
<p>They store anything that is found in the atmosphere, such as atmospheric gases, pollen, microbes, emissions from volcanic eruptions, dust and salts carried by dust storms from deserts and salt flats, agricultural and grazing lands. They even can record ocean spray along with pollutants from human activities such as lead, mercury and <a href="https://www.epa.gov/radiation/radionuclides">radioactive nuclides</a> from thermonuclear bomb tests. </p>
<p>Ice also preserves records of past temperature in the changing isotopic composition of water, and provides histories of snowfall by the thicknesses of ice that has formed each year.</p>
<figure class="align-center ">
<img alt="Three ice cores recovered from different depths." src="https://images.theconversation.com/files/355642/original/file-20200831-19-2fbq7h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/355642/original/file-20200831-19-2fbq7h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=175&fit=crop&dpr=1 600w, https://images.theconversation.com/files/355642/original/file-20200831-19-2fbq7h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=175&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/355642/original/file-20200831-19-2fbq7h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=175&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/355642/original/file-20200831-19-2fbq7h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=220&fit=crop&dpr=1 754w, https://images.theconversation.com/files/355642/original/file-20200831-19-2fbq7h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=220&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/355642/original/file-20200831-19-2fbq7h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=220&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">Relatively young and shallow snow becomes packed into coarse and granular crystals called firn (top: 53 meters deep). Older and deeper snow is compacted further (middle: 1,836 meters). At the bottom of a core (lower: 3,050 meters), rocks, sand and silt discolor the ice. (Photographs courtesy U.S. National Ice Core Laboratory)</span>
<span class="attribution"><a class="source" href="https://earthobservatory.nasa.gov/features/Paleoclimatology_IceCores">U.S. National Ice Core Laboratory</a></span>
</figcaption>
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<h2>How can studying ice cores help learn about historical events?</h2>
<p>Ice cores provide independent histories of past climate and environmental change that can often be compared to written and archaeological records of human history. This is especially true in the lower latitudes where earlier cultures rose and fell. For example, ice cores from the <a href="https://news.osu.edu/documenting-the-demise-of-quelccaya-the-worlds-largest-tropical-ice-cap/">Quelccaya ice cap</a> in the southern Peruvian Andes provide a nearly 2,000 year-by-year history of tropical climate that has helped anthropologists study how changes in temperature, and annual precipitation and drought patterns tracked the rise and fall of ancient Andean civilizations. For example, a major drought, recorded by precipitation (snowfall) and dust records in the Quelccaya cores, may have played a role in the <a href="https://www.smithsonianmag.com/science-nature/chronicling-the-ice-156979331/">demise of the Tiwanaku civilization</a> around the year 1000. </p>
<p>Abrupt global events and “black swans,” or rare but impactful events, have been observed using ice core-derived paleoclimate information from high elevation tropical mountains. For example, evidence of the so-called “<a href="https://doi.org/10.1177/097194580701000203">East India Drought</a>” in the late 18th century was noticed in ice cores from both the Peruvian Andes and the Himalayas. This drought was partially responsible for <a href="https://doi.org/10.1007/s00382-019-04694-4">million of deaths in India</a>. This was a time when several successive El Niños occurred and were linked with the failure of the monsoon rains and decreasing precipitation in parts of tropical South America. Severe droughts were also documented in Egypt, Java, Australia, Mexico and the Caribbean. Great <a href="https://doi.org/10.1177/097194580701000203">social upheavals</a>, including four civil wars, occurred around the world. </p>
<p>Further back in time, several tropical ice core records contain evidence of <a href="https://www.wired.com/beyond-the-beyond/2018/08/collapse-civilizations-worldwide-defines-youngest-unit-geologic-time-scale/">a major worldwide drought</a> about 4,200 years ago. This occurred during the rapid decline of the Akkadian Empire in Mesopotamia, the Harappan civilization in the Indus Valley, the so-called Old Kingdom in Egypt and the Longshan Culture in East China. </p>
<h2>What kind of evidence would the current pandemic leave in the ice?</h2>
<p>Some <a href="https://doi.org/10.1002/2017GH000064">ice core records show</a> that during the mid-1300s there was less lead in the atmosphere, possibly related to the sharp drop in mining and smelting activities. This coincided with the appearance of the plague known as the “Black Death” in Europe and Asia. This decrease in human industrial activity is analogous to what is happening now during the current COVID-19 pandemic. Throughout the world people are traveling less, resulting in a <a href="https://theconversation.com/covid-19-shutdowns-are-clearing-the-air-but-pollution-will-return-as-economies-reopen-134610">reduction in emissions of carbon dioxide, nitrogen dioxide and sulfur dioxide</a> into the atmosphere. Future glaciologists will likely see decreases in these gases and their chemical derivatives in ice cores.</p>
<h2>As glaciers around the world recede due to climate change, how will it affect our ability to study the past?</h2>
<p>Ice cores stored in freezer facilities become extremely important for future research as these unique archives of our past melt away on our warming Earth. The world’s ice is melting at an accelerating rate and this ice melt has already led to the major shrinking or loss of the smaller and very sensitive mountain glaciers in the Tropics such as some glaciers on Kilimanjaro and virtually all glaciers in Papua, Indonesia (New Guinea), where soon <a href="https://doi.org/10.1073/pnas.1822037116">all the ice is likely to disappear</a>. </p>
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<img alt="A 3d render of the Puncak Jaya glacier in Indonesia" src="https://images.theconversation.com/files/355645/original/file-20200831-14-1jxznmw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/355645/original/file-20200831-14-1jxznmw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/355645/original/file-20200831-14-1jxznmw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/355645/original/file-20200831-14-1jxznmw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/355645/original/file-20200831-14-1jxznmw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/355645/original/file-20200831-14-1jxznmw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/355645/original/file-20200831-14-1jxznmw.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">
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<span class="caption">A 3D render of a glacier on the Puncak Jaya peak in Indonesia.</span>
<span class="attribution"><span class="source">Google Earth / Maxar Technologies</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
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<h2>What are the possible impacts of receding glaciers in the areas that you study?</h2>
<p><a href="https://doi.org/10.1038/s41598-018-33698-z">As mountain glaciers disappear</a> and the streams and rivers that arise from them are affected, nearby communities, and to a lesser extent communities further downstream, face the greatest economic and societal consequences, including disruptions to agriculture, hydropower generation, urban water supply and tourism. In many places such as the Andes and Himalayas, glaciers have deep historical, cultural, and even spiritual meaning to the people who live in their shadows. </p>
<p>For example, since our first studies of the Quelccaya ice cap in southern Peru in 1974, we have been interacting with people in the local communities just to the west. Since the mid-1970s, Quelccaya has lost almost 40% of its area.<strong>link</strong> During the dry season, many of the grasslands that feed the herds of alpacas, llamas and sheep of the people in Phinaya, a local semi-nomadic pastoralist community, can be irrigated only with the water that runs off the ice cap and other glaciated peaks that are part of their territorial domain. </p>
<p>Quelccaya is also considered a very important apu, or sacred mountain, local deity, and ancestor. We encountered similar beliefs in Bolivia and in Papua, Indonesia (New Guinea).</p>
<p>The melting of mountain glaciers also presents hazards to local communities. Melting ice forms new lakes along the glacier margins, and the water is held back by natural dams which often fail. For example, we have mapped the <a href="https://news.osu.edu/documenting-the-demise-of-quelccaya-the-worlds-largest-tropical-ice-cap/">retreat of Quelccaya’s Qori Kalis</a> outlet glacier since 1978. A lake started forming in this valley in 1991 and grew to cover 84 acres and to be 200 ft deep. In March 2006, an avalanche from the ice cap fell into the lake, causing the lake to overtop the moraine dam and drown grazing alpaca along the outlet stream.</p>
<figure class="align-center ">
<img alt="A satellite image of lakes formed by melting glaciers in Bhutan" src="https://images.theconversation.com/files/355635/original/file-20200831-20-wxnr2o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/355635/original/file-20200831-20-wxnr2o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/355635/original/file-20200831-20-wxnr2o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/355635/original/file-20200831-20-wxnr2o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/355635/original/file-20200831-20-wxnr2o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=420&fit=crop&dpr=1 754w, https://images.theconversation.com/files/355635/original/file-20200831-20-wxnr2o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=420&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/355635/original/file-20200831-20-wxnr2o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=420&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This ASTER image shows the lakes left behind by retreating glaciers in the Bhutan-Himalaya.</span>
<span class="attribution"><a class="source" href="https://earthobservatory.nasa.gov/features/GLIMS">Jeffrey Kargel / USGS/NASA</a></span>
</figcaption>
</figure>
<p>[<em>Deep knowledge, daily.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=deepknowledge">Sign up for The Conversation’s newsletter</a>.]</p><img src="https://counter.theconversation.com/content/144784/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lonnie Thompson receives funding from the NSF Paleoclimatology program and The Ohio State University</span></em></p><p class="fine-print"><em><span>Ellen Mosley-Thompson receives funding from NSF Paleoclimatology program and The Ohio State University</span></em></p>Ice cores can preserve evidence of ‘black swan’ events like pandemics and droughts, but the glaciers from which they are collected are disappearing.Lonnie Thompson, Distinguished University Professor, Earth Sciences, The Ohio State UniversityEllen Mosley-Thompson, Distinguished University Professor, Geography (Atmospheric Sciences), Senior Research Scientist, The Ohio State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1417842020-07-07T19:52:07Z2020-07-07T19:52:07ZClimate explained: what the world was like the last time carbon dioxide levels were at 400ppm<figure><img src="https://images.theconversation.com/files/345916/original/file-20200706-3943-1sq2bv1.jpg?ixlib=rb-1.1.0&rect=33%2C92%2C5573%2C3640&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Gil.K/Shutterstock</span></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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<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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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>
<hr>
<blockquote>
<p><strong>What was the climate and sea level like at times in Earth’s history when carbon dioxide in the atmosphere was at 400ppm?</strong></p>
</blockquote>
<p>The last time global carbon dioxide levels were consistently at or above 400 parts per million (ppm) was around <a href="https://www.nature.com/articles/nature14145">four million years ago</a> during a geological period known as the <a href="http://www.geologypage.com/2014/05/pliocene-epoch.html">Pliocene Era</a> (between 5.3 million and 2.6 million years ago). The world was about 3°C warmer and sea levels were higher than today. </p>
<p>We know how much carbon dioxide the atmosphere contained in the past by studying ice cores from Greenland and Antarctica. As compacted snow gradually changes to ice, it traps air in bubbles that contain <a href="https://www.cambridge.org/core/journals/annals-of-glaciology/article/enclosure-of-air-during-metamorphosis-of-dry-firn-to-ice/09D9C60A8DA412D16645E6E6ABC1892F">samples of the atmosphere at the time</a>. We can sample ice cores to reconstruct past concentrations of carbon dioxide, but this record only takes us back about a million years.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/climate-explained-what-caused-major-climate-change-in-the-past-137874">Climate explained: what caused major climate change in the past?</a>
</strong>
</em>
</p>
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<p>Beyond a million years, we don’t have any direct measurements of the composition of ancient atmospheres, but we can use several methods to estimate past levels of carbon dioxide. One method uses the relationship between plant pores, known as stomata, that regulate gas exchange in and out of the plant. The density of these stomata is <a href="https://journals.sagepub.com/doi/abs/10.1177/095968369200200109">related to atmospheric carbon dioxide</a>, and fossil plants are a good indicator of concentrations in the past.</p>
<p>Another technique is to examine sediment cores from the ocean floor. The sediments build up year after year as the bodies and shells of dead plankton and other organisms rain down on the seafloor. We can use isotopes (chemically identical atoms that differ only in atomic weight) of boron taken from the shells of the dead plankton to reconstruct changes in the acidity of seawater. From this we can work out the level of carbon dioxide in the ocean. </p>
<p>The data from four-million-year-old sediments suggest that <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010PA002055">carbon dioxide was at 400ppm back then</a>.</p>
<h2>Sea levels and changes in Antarctica</h2>
<p>During colder periods in Earth’s history, ice caps and glaciers grow and sea levels drop. In the recent geological past, during the most recent ice age about 20,000 years ago, sea levels were at least <a href="https://science.sciencemag.org/content/292/5517/679.abstract">120 metres lower</a> than they are today.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/345976/original/file-20200707-26-1nsf11x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/345976/original/file-20200707-26-1nsf11x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/345976/original/file-20200707-26-1nsf11x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/345976/original/file-20200707-26-1nsf11x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/345976/original/file-20200707-26-1nsf11x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/345976/original/file-20200707-26-1nsf11x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/345976/original/file-20200707-26-1nsf11x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Recent research shows that west Antarctica is now melting.</span>
<span class="attribution"><span class="source">Elaine Hood/NSF</span></span>
</figcaption>
</figure>
<p>Sea-level changes are calculated from changes in isotopes of oxygen in the shells of marine organisms. For the Pliocene Era, <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2004PA001071">research</a> shows the sea-level change between cooler and warmer periods was around 30-40 metres and sea level was higher than today. Also during the Pliocene, we know the West Antarctic Ice Sheet was <a href="https://www.nature.com/articles/nature07867">significantly smaller</a> and global average temperatures were about 3°C warmer than today. Summer temperatures in high northern latitudes were up to 14°C warmer. </p>
<p>This may seem like a lot but modern observations show strong <a href="https://journals.ametsoc.org/jcli/article/23/14/3888/32547">polar amplification</a> of warming: a 1°C increase at the equator may raise temperatures at the poles by 6-7°C. It is one of the reasons why Arctic sea ice is disappearing. </p>
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<p>
<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>
<hr>
<h2>Impacts in New Zealand and Australasia</h2>
<p>In the Australasian region, there was no Great Barrier Reef, but there may have been <a href="https://link.springer.com/content/pdf/10.1007/BF02537376.pdf">smaller reefs along the northeast coast of Australia</a>. For New Zealand, the partial melting of the West Antarctic Ice Sheet is probably the most critical point. </p>
<p>One of the key features of New Zealand’s current climate is that Antarctica is cut off from global circulation during the winter because of the big <a href="https://www.tandfonline.com/doi/abs/10.3402/tellusa.v54i5.12161">temperature contrast</a> between Antarctica and the Southern Ocean. When it comes back into circulation in springtime, New Zealand gets strong storms. Stormier winters and significantly warmer summers were likely in the mid-Pliocene because of a weaker polar vortex and a warmer Antarctica.</p>
<p>It will take more than a few years or decades of carbon dioxide concentrations at 400ppm to trigger a significant shrinking of the West Antarctic Ice Sheet. But recent studies show that <a href="http://nora.nerc.ac.uk/id/eprint/521027/">West Antarctica is already melting</a>. </p>
<p>Sea-level rise from a partial melting of West Antarctica could easily exceed a metre or more by 2100. In fact, if the whole of the West Antarctic melted it could <a href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.695.7239&rep=rep1&type=pdf">raise sea levels by about 3.5 metres</a>. Even smaller increases raise the risk of <a href="https://www.pce.parliament.nz/publications/preparing-new-zealand-for-rising-seas-certainty-and-uncertainty">flooding in low-lying cities</a> including Auckland, Christchurch and Wellington.</p><img src="https://counter.theconversation.com/content/141784/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Shulmeister receives funding from the Australian Research Council and is part of a National Science Foundation grant from the US. As well as being Professor and Head of School at the University of Canterbury in New Zealand, he is an Adjunct Professor at the University of Queensland, Australia and an associate investigator at the ARC Centre of Excellence for Australian Biodiversity and Heritage (CABAH)</span></em></p>The last time global carbon dioxide levels were around 400ppm was four million years ago. On average, the world was 3°C warmer, but in high northern latitudes, it was up to 14°C warmer than today.James Shulmeister, Professor, University of CanterburyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1411962020-06-22T19:05:49Z2020-06-22T19:05:49ZDid a volcanic eruption in Alaska help end the Roman republic?<figure><img src="https://images.theconversation.com/files/343206/original/file-20200622-54981-zagf3c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The death of Caesar.</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Assassination_of_Julius_Caesar#/media/File:Vincenzo_Camuccini_-_La_morte_di_Cesare.jpg">Vincenzo Camuccini/Wikipedia</a></span></figcaption></figure><p>Julius Caesar was assassinated on the Ides of March (March 15) in 44BC and a bloody civil war followed. This brought down the Roman republic and replaced it with a monarchy led by Caesar’s nephew Octavian, who in 27BC became the emperor Augustus. A group of scientists and historians suggest that a massive volcanic eruption in Alaska played a role in this transition, as well as helping to finish off Cleopatra’s Egypt. </p>
<p><a href="https://www.pnas.org/cgi/doi/10.1073/pnas.2002722117">The study</a>, led by Joseph R McConnell of the Desert Research Institute in Nevada, demonstrates how careful scientific research on ancient climate can add context to our more traditional scholarship. At the same time, the research raises challenging questions about how we integrate such data into historical narratives without oversimplifying the story.</p>
<p>Caesar’s assassination came at a time of unrest for the ancient Mediterranean. This was exacerbated by strange atmospheric phenomena, and unusually cold, wet weather that caused crop failures, food shortages, disease, and even the failure of the annual Nile flood on which Egyptian agriculture relied. In 1988, classicist Phyllis Forsyth <a href="https://doi.org/10.2307/25010878">suggested that</a> an eruption of Mount Etna in Sicily in 44BC was responsible for these problems because the aerosol particles released into the atmosphere would reflect sunlight back into space and cool the climate.</p>
<p>While McConnell’s team agreed that the Etna eruption could have caused some of these disruptions, they have now argued it was a later massive eruption of the Okmok volcano in Alaska that altered the climate and helped weaken the Roman and Egyptian states. They drew on three strands of evidence to support their claim.</p>
<p>The first came from ice samples taken from deep in the Arctic ice sheets, which trapped air as they formed over hundreds of thousands of years, providing a datable record of atmospheric conditions. These <a href="https://climate.nasa.gov/news/2616/core-questions-an-introduction-to-ice-cores/">ice cores</a> showed there was a spike in solid particles, dust and ash from a volcanic eruption early in 43BC. The researchers then showed the geochemical properties of these particles matched with samples from the Okmok volcano.</p>
<p>For evidence for the ancient climate, they then looked at tree rings and speleothems (stalactites and stalagmites) from various parts of the northern hemisphere, including China, Europe and North America. These suggested that 43BC to 34BC was the fourth coldest decade in the last 2,500 years, and 43BC and 42BC were the second and eighth coldest years.</p>
<p>Data from the research was then fed into a computer-based climate modelling system called the <a href="http://www.cesm.ucar.edu/">Community Earth System Model</a> (CESM), which produced a climate simulation. This showed that the eruption of Okmok could have caused cooling of 0.7˚C to 7.4˚C across the southern Mediterranean and northern Africa in 43-42BC, which persisted into the 30s BC. </p>
<p>This could also have led to increased summer and autumn rainfall that would have damaged crops. At the same time, drier conditions in the upper reaches of the Nile may have led to its failure to flood in 43BC and 42BC.</p>
<p>In this way, McConnell’s team make a good case for Okmok’s potential impact on temperature, rainfall and a resulting change in agricultural production in 43BC and after. But the conclusions they draw about its impact on the bigger historical picture are less certain. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/343278/original/file-20200622-55001-12l79o4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/343278/original/file-20200622-55001-12l79o4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=242&fit=crop&dpr=1 600w, https://images.theconversation.com/files/343278/original/file-20200622-55001-12l79o4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=242&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/343278/original/file-20200622-55001-12l79o4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=242&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/343278/original/file-20200622-55001-12l79o4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=304&fit=crop&dpr=1 754w, https://images.theconversation.com/files/343278/original/file-20200622-55001-12l79o4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=304&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/343278/original/file-20200622-55001-12l79o4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=304&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The 10-km wide caldera on Alaska’s Unmak Island formed during the 43 BCE Okmok II eruption..</span>
<span class="attribution"><span class="source">Kerry Key (Columbia University, New York, NY)</span></span>
</figcaption>
</figure>
<p>One of the major problems with scientific papers in which climate events are blamed for major historical changes is that they are not able to fit in much analysis of the historical issues themselves. These tend to be reduced to straightforward events or problems that can then be easily “explained” or “solved” by science. The realities, when we zoom in, are much more messy.</p>
<p>The transition of Rome from a republic to a monarchy – via a period of rule by the competing triumvirate of Octavian, Mark Antony and Lepidus – was a long and complex process. It involved <a href="https://www.cambridge.org/core/books/roman-power/romans-against-each-other-from-republic-to-monarchy/85B34D739964F8FC708247CF89424EEF">many people and parties</a> with different motivations and plans. The whole period poses a challenge to historians and <a href="https://global.oup.com/academic/product/the-roman-revolution-9780192803207?cc=gb&lang=en&">entire books</a> have sought to describe and explain it. </p>
<p>But this civil war was only the latest in a series of escalating conflicts in the later period of the republic, in which the behaviour of earlier figures, like Sulla, who had seized control of Rome decades earlier, became precedents for <a href="https://www.cambridge.org/core/books/rome-and-the-making-of-a-world-state-150-bce20-ce/spiral-of-violence-10480-bce/38567A53DDAAAF43D30F5AE8E7943E2F">what might be possible</a>. </p>
<p>The outcome of the war and the establishment of a monarchy was not inevitable. Rather than a narrative of crisis, decline and fall, the period can even be seen as one of <a href="https://www.cambridge.org/core/books/rome-and-the-making-of-a-world-state-150-bce20-ce/war-of-the-world-4930-bce/5E4B8CEEA17CF250A20E5A2BF46B59DA">political experimentation</a>, of state formation, of attempts to solve the problems that beset the republic.</p>
<h2>More complicated picture</h2>
<p>This period of war relied on manpower and the capacity of state apparatus to extract and redirect food and money from society. Despite ancient sources that report difficulties with this extraction, we should remember that the machinery that enabled it remained essentially in working order. Without it, armies would not have been fed and the civil wars would not have been able to happen. </p>
<p>And while the failure of the Nile floods in 43BC and 42BC would certainly have been bad, Egypt was up and running again soon after. Antony and Cleopatra were able to raise and maintain armies, fight, and were finally defeated only in 31BC in the naval battle of Actium. If people were going hungry, the conflict itself and profiteering grain dealers were perhaps more to blame than the climate (as was the case in <a href="https://www.hrw.org/sites/default/files/reports/Ethiopia919.pdf">the Ethiopian famines of the 1980s</a>).</p>
<p>The effects of Okmok’s eruption in 43BC may have been serious, as McConnell’s team argue. But it is also very clear that personal, political and military decisions – and chance – were the direct determiners of how history unfolded in Rome and Egypt. There were many points in the years after 44 BC at which things could have turned out quite differently, whatever the climate was like. </p>
<p>The military activity of the period alone would seem to show that both Rome and Egypt were quite resilient, overall, in the face of natural hazards, and as states they continued to transform in an ever-changing world.</p><img src="https://counter.theconversation.com/content/141196/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Guy D. Middleton receives funding from the European Regional Development Fund-Project “Creativity and Adaptability as Conditions of the Success of Europe in an Interrelated World” (no. CZ.02.1.01/0.0/0.0/16_019/0000734).</span></em></p>New research suggests ancient climate change shaped the fate of western civilisation.Guy Middleton, Visiting Fellow, School of History, Classics and Archaeology, Newcastle UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/829022017-08-23T19:22:43Z2017-08-23T19:22:43ZAntarctic ice reveals that fossil fuel extraction leaks more methane than thought<figure><img src="https://images.theconversation.com/files/183132/original/file-20170823-13299-1u60k1n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The analysis of large amounts of ice from Antarctica's Taylor Valley has helped scientists to tease apart the natural and human-made sources of the potent greenhouse gas methane.</span> <span class="attribution"><span class="source">Hinrich Schaefer</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>The fossil fuel industry is a larger contributor to atmospheric methane levels than previously thought, according to our research which shows that natural seepage of this potent greenhouse gas from oil and gas reservoirs is more modest than had been assumed.</p>
<p>In our research, <a href="http://www.nature.com/articles/doi:10.1038/nature23316">published in Nature today</a>, our international team studied Antarctic ice dating back to the last time the planet warmed rapidly, roughly 11,000 years ago. </p>
<figure>
<iframe src="https://player.vimeo.com/video/67359077" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">Katja Riedel and Hinrich Schaefer discuss NIWA’s ice coring work at Taylor Glacier in Antarctica.</span></figcaption>
</figure>
<p>We found that natural seepage of methane from oil and gas fields is much lower than anticipated, implying that leakage caused by fossil fuel extraction has a larger role in today’s emissions of this greenhouse gas.</p>
<p>However, we also found that vast stores of methane in permafrost and undersea gas hydrates did not release large amounts of their contents during the rapid warming at the end of the most recent ice age, relieving fears of a catastrophic methane release in response to the current warming. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/183135/original/file-20170823-13271-14o5tbc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/183135/original/file-20170823-13271-14o5tbc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/183135/original/file-20170823-13271-14o5tbc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/183135/original/file-20170823-13271-14o5tbc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/183135/original/file-20170823-13271-14o5tbc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/183135/original/file-20170823-13271-14o5tbc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/183135/original/file-20170823-13271-14o5tbc.jpg?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">
<figcaption>
<span class="caption">The ice is processed in a large melter before samples are shipped back to New Zealand.</span>
<span class="attribution"><span class="source">Hinrich Schaefer</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>A greenhouse gas history</h2>
<p>Methane levels <a href="http://onlinelibrary.wiley.com/doi/10.1029/2006GL026152/full">started to increase with the industrial revolution</a> and <a href="http://www.nature.com/nature/journal/v453/n7193/full/nature06950.html">are now 2.5 times higher than they ever were naturally</a>. They have caused <a href="http://science.sciencemag.org/content/326/5953/716">one-third of the observed increase in global average temperatures</a> relative to pre-industrial times. </p>
<p>If we are to reduce methane emissions, we need to understand where it comes from. Quantifying different sources is notoriously tricky, but it is especially hard when natural and human-driven emissions happen at the same time, through similar processes. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/detecting-methane-leaks-with-infrared-cameras-theyre-fast-but-are-they-effective-70249">Detecting methane leaks with infrared cameras: They're fast, but are they effective?</a>
</strong>
</em>
</p>
<hr>
<p>The most important of these cases is natural methane seepage from oil and gas fields, also known as geologic emissions, which often occurs alongside leakage from production wells and pipelines. </p>
<p>The total is reasonably well known, but where is the split between natural and industrial?</p>
<p>To make matters worse, human-caused climate change could destabilise permafrost or ice-like sediments called gas hydrates (or clathrates), both of which have the potential to release more methane than any human activity and reinforce climate change. This scenario has been hypothesised for past warming events (the “clathrate gun”) and for future runaway climate change (the so-called “Arctic methane bomb”). But how likely are these events? </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/183134/original/file-20170823-13285-16053hy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/183134/original/file-20170823-13285-16053hy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/183134/original/file-20170823-13285-16053hy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/183134/original/file-20170823-13285-16053hy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/183134/original/file-20170823-13285-16053hy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/183134/original/file-20170823-13285-16053hy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/183134/original/file-20170823-13285-16053hy.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">Antarctic ice traps tiny bubbles of air, which represents a sample of ancient atmospheres.</span>
<span class="attribution"><span class="source">Hinrich Schaefer</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>The time capsule</h2>
<p>To find answers, we needed a time capsule. This is provided by tiny air bubbles enclosed in polar ice, which preserve ancient atmospheres. By using radiocarbon (14C) dating to determine the age of methane from the end of the last ice age, we can work out how much methane comes from contemporary processes, like wetland production, and how much is from previously stored methane. During the time the methane is stored in permafrost, sediments or gas fields, the 14C decays away so that these sources emit methane that is radiocarbon-free. </p>
<p>In the absence of strong environmental change and industrial fossil fuel production, all radiocarbon-free methane in samples from, say, 12,000 years ago will be from geologic emissions. From that baseline, we can then see if additional radiocarbon-free methane is released from permafrost or hydrates during rapid warming, which occurred around 11,500 years ago while methane levels shot up. </p>
<h2>Tracking methane in ice</h2>
<p>The problem is that there is not much air in an ice sample, very little methane in that air, and a tiny fraction of that methane contains a radiocarbon (14C) atom. There is no hope of doing the measurements on traditional ice cores. </p>
<p>Our team therefore went to Taylor Glacier, in the Dry Valleys of Antarctica. Here, topography, glacier flow and wind force ancient ice layers to the surface. This provides virtually unlimited sample material that spans the end of the last ice age. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/183136/original/file-20170823-13285-gv9u10.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/183136/original/file-20170823-13285-gv9u10.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/183136/original/file-20170823-13285-gv9u10.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/183136/original/file-20170823-13285-gv9u10.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/183136/original/file-20170823-13285-gv9u10.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/183136/original/file-20170823-13285-gv9u10.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/183136/original/file-20170823-13285-gv9u10.jpg?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">
<figcaption>
<span class="caption">A tonne of ice yielded only a drop of methane.</span>
<span class="attribution"><span class="source">Hinrich Schaefer</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>For a single measurement, we drilled a tonne of ice (equivalent to a cube with one-metre sides) and melted it in the field to liberate the enclosed air. From the gas-tight melter, the air was transferred to vacuum flasks and shipped to New Zealand. In the laboratory, we extracted the pure methane out of these 100-litre air samples, to obtain a volume the size of a water drop. </p>
<p>Only every trillionth of the methane molecules contains a 14C atom. Our collaborators in Australia were able to measure exactly how big that minute fraction is in each sample and if it changed during the studied period. </p>
<h2>Low seepage, no gun, no bomb</h2>
<p>Because radiocarbon decays at a known rate, the amount of 14C gives a radiocarbon age. In all our samples the radiocarbon date was consistent with the sample age. </p>
<p>Radiocarbon-free methane emissions did not increase the radiocarbon age. They must have been very low in pre-industrial times, even during a rapid warming event. The latter indicates that there was no clathrate gun or Arctic methane bomb going off. </p>
<p>So, while today’s conditions differ from the ice-covered world 12,000 years ago, our findings implicate that permafrost and gas hydrates are not too likely to release large amounts of methane in future warming. That is good news. </p>
<p>Wetlands must have been responsible for the increase in methane at the end of the ice age. They have a lesser capacity for emissions than the immense permafrost and clathrate stores. </p>
<p>Geologic emissions are likely to be lower today than in the ice age, partly because we have since drained shallow gas fields that are most prone to natural seepage. Yet, our highest estimates are only about half of the lower margin estimated for today. The total assessment (natural plus industrial) for fossil-fuel methane emissions <a href="http://www.nature.com/nature/journal/v538/n7623/full/nature19797.html">has recently been increased</a>. </p>
<p>In addition, we now find that a larger part of that must come from industrial activities, raising the latter to one third of all methane sources globally. For comparison, <a href="https://www.ipcc.ch/report/ar5/wg1/">the last IPCC report</a> put them at 17%.</p>
<p><a href="http://science.sciencemag.org/content/352/6281/80">Measurements in modern air</a> suggest that the rise in methane levels over the last years is dominated by agricultural emissions, which must therefore be mitigated. Our new research shows that the impact of fossil fuel use on the historic methane rise is larger than assumed. In order to mitigate climate change, methane emissions from oil, gas and coal production must be cut sharply.</p><img src="https://counter.theconversation.com/content/82902/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hinrich Schaefer works for the National Institute of Water and Atmospheric Research.
He has received funding from the New Zealand Government through Strategic Science Investment Funds and a Marsden Grant.
In previous positions, his work has received government funding from Germany, the European Union, Canada and the USA, as well as a grant from the American Chemical Society. </span></em></p>Analysis of 12,000-year-old Antarctic ice reveals that methane leaks from fossil fuel extraction play a larger role than previously thought.Hinrich Schaefer, Research Scientist Trace Gases, National Institute of Water and Atmospheric ResearchLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/730452017-02-20T04:14:50Z2017-02-20T04:14:50ZFactCheck Q&A: was it four degrees hotter 110,000 years ago?<figure><img src="https://images.theconversation.com/files/157278/original/image-20170217-4271-6avur5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Senator Jacqui Lambie, speaking on Q&A.</span> <span class="attribution"><span class="source">Q&A</span></span></figcaption></figure><p><strong>The Conversation fact-checks claims made on Q&A, broadcast Mondays on the ABC at 9:35pm. Thank you to everyone who sent us quotes for checking via <a href="http://www.twitter.com/conversationEDU">Twitter</a> using hashtags #FactCheck and #QandA, on <a href="http://www.facebook.com/conversationEDU">Facebook</a> or by <a href="mailto:checkit@theconversation.edu.au">email</a>.</strong></p>
<hr>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/VunHZ7cCCyw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
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<blockquote>
<p>JACQUI LAMBIE: First of all, we’ve always had climate change – it’s been much, much hotter and much, much colder. Even 110,000 years ago, it was four degrees hotter. Charging our pensioners and our businesses and families more for power…</p>
<p>TONY JONES: There’ll be fact checkers on that one, Jacqui…– <strong>Tasmanian senator Jacqui Lambie, <a href="http://www.abc.net.au/tv/qanda/txt/s4612398.htm">speaking on Q&A</a> with host Tony Jones, February 13, 2017</strong></p>
</blockquote>
<p>With renewable energy, heatwaves and climate change back in the headlines, Tasmanian senator Jacqui Lambie told Q&A that it was four degrees hotter 110,000 years ago.</p>
<p>Is that right?</p>
<h2>Checking the source</h2>
<p>When asked for sources to support her statement, a spokesman for Jacqui Lambie referred The Conversation to Al Gore’s book <a href="https://www.amazon.com/Inconvenient-Truth-Planetary-Emergency-Warming/dp/B000QEJ0WY">An Inconvenient Truth</a> and Tim Flannery’s book <a href="http://www.theweathermakers.org/">The Weather Makers</a>.</p>
<p>The spokesman confirmed that Lambie was referring to 4°C, not Fahrenheit, and added:</p>
<blockquote>
<p>… most people think that the average world temperature has been constant for millions of years. The Gore and Flannery books prove it hasn’t.</p>
</blockquote>
<p>The detailed response from Lambie’s office, which is available <a href="http://theconversation.com/full-response-from-a-spokesperson-for-jacqui-lambie-for-a-factcheck-on-climate-change-73064">here</a>, included a chart from Gore’s book An Inconvenient Truth, which Lambie’s office had annotated. That chart is based on <a href="https://www.ncdc.noaa.gov/paleo-search/study/6080">data</a> from <a href="http://science.sciencemag.org/content/317/5839/793">Antarctic ice cores</a>. A response that The Conversation sourced from Tim Flannery on Lambie’s representation of his work can also be found <a href="http://theconversation.com/full-response-from-a-spokesperson-for-jacqui-lambie-for-a-factcheck-on-climate-change-73064">here</a>. </p>
<p>Let’s check the scientific evidence.</p>
<h2>Warmer, compared to what?</h2>
<p>Most non-scientists probably think in terms of “warmer than today” or “cooler than today”.</p>
<p>However, much of the science on this compares past and projected temperatures to a <a href="https://www.climate-lab-book.ac.uk/2017/defining-pre-industrial/">pre-industrial baseline</a>, not to the temperature today in 2017. That’s because temperatures now are rising too rapidly to serve as a useful baseline. (Industrialisation began in the late 18th century, and the world has warmed by <a href="https://climate.nasa.gov/evidence/">about 1°C since then</a>).</p>
<p>In this FactCheck, we will talk about both: comparing to pre-industrial levels and comparing to today.</p>
<h2>Was it ‘much, much hotter’ and ‘much, much colder’ in the past?</h2>
<p>Lambie was right to say that the Earth’s climate has always changed and that, at different times, Earth has been hotter and colder than today.</p>
<p>The past 650,000 years of Earth’s history (the interval shown in the annotated chart provided by Lambie’s office) was characterised by large climate swings as Earth moved naturally in and out of “ice ages” <a href="https://theconversation.com/ice-ages-have-been-linked-to-the-earths-wobbly-orbit-but-when-is-the-next-one-70069">triggered by changes in its orbit relative to the Sun</a>. </p>
<p>Initial cooling, brought on by slow changes to the shape of the Earth’s orbit and wobble of the Earth’s axis, was <a href="https://www.epa.gov/climate-change-science/causes-climate-change">amplified by natural effects</a>, including the growing ice sheets and the drawing down of carbon dioxide into the deep oceans. Over tens of thousands of years these <a href="https://www.theguardian.com/environment/2011/jan/05/climate-change-feedback-loops">amplifying feedbacks</a> caused Earth’s climate to descend into an ice age. </p>
<p>At the peak of the last ice age (around 20,000 years ago), Earth’s global average temperature is estimated by scientists to have been about <a href="http://www.nature.com/nature/journal/v538/n7624/full/nature19798.html">5-6°C cooler</a> than it was during the pre-industrial interval.</p>
<p>So, yes, it is fair to describe the ice ages as much, much colder than now. But were the warm periods of the last 650,000 years “much, much hotter”? </p>
<p>No. The warm climates of the so-called “interglacials” – meaning the period between ice ages – were similar to today. <a href="http://www.nature.com/nature/journal/v538/n7624/full/nature19798.html">A few of these periods</a> were a little bit hotter; some were a little bit cooler. </p>
<p>None had a <em>global</em> average temperature that was 4°C warmer than either today or pre-industrial times (we will return later to what the data say about <em>local</em> average temperatures).</p>
<h2>How warm was it 110,000 or so years ago?</h2>
<p>There was a warm interglacial period <a href="http://www.sciencedirect.com/science/article/pii/S0277379114003382">around 130,000 to 115,000 years ago</a>, before the last ice age. </p>
<p>This last interglacial period <em>was</em> one of the warmest periods of the past 650,000 years. But it wasn’t 4°C hotter globally. </p>
<p>Extensive <a href="http://rsta.royalsocietypublishing.org/content/371/2001/20130097">scientific evidence from across the globe</a> shows that the global average temperature during this interglacial period was <a href="http://www.nature.com/nature/journal/v538/n7624/full/nature19798.html">1-2°C warmer</a> than pre-industrial times (or about as warm as it was in 2016).</p>
<p>This evidence comes from <a href="https://www.ncdc.noaa.gov/news/what-are-proxy-data">natural climate archives</a>, including the tiny marine organisms that <a href="http://icestories.exploratorium.edu/dispatches/big-ideas/ice-and-sediment-cores/">accumulate as sediment on the bottom of the oceans</a> and whose chemical makeup fluctuates with surface ocean temperatures, and the <a href="https://theconversation.com/explainer-what-are-ice-cores-24302">water molecules in ice cores</a> that reflect air temperatures over the polar regions.</p>
<p>The last time Earth’s average temperature was 4°C warmer than pre-industrial levels was around <a href="http://rsta.royalsocietypublishing.org/content/371/2001/20120294">5-10 million years ago</a>. To put that in context, modern humans have existed for the last 200,000 years and civilised societies began to form only around 6,000 years ago.</p>
<h2>Global average temperatures versus local warming</h2>
<p>While the global average temperature during the last interglacial period was 1-2°C warmer than pre-industrial times, in some places like Antarctica and Greenland <em>local</em> warming resulted in temperatures as high as, <a href="http://www.nature.com/nature/journal/v493/n7433/full/nature11789.html">or even higher than</a>, 4°C warmer. These more extreme <em>local</em> temperature changes near the poles are referred to as
<a href="http://www.realclimate.org/index.php/archives/2006/01/polar-amplification/">polar amplification</a>.</p>
<p>Scientists have used ice-core data to calculate that during the last interglacial period Antarctica was around <a href="https://www.ncdc.noaa.gov/paleo/study/6080">3-5°C warmer</a> than it was during pre-industrial times. But <em>global</em> average temperatures were not 4°C warmer. </p>
<h2>Why does it matter?</h2>
<p>The fact that Earth has experienced natural climate changes in the past doesn’t downplay the significance of how humans are changing the climate now. </p>
<p>The vast amounts of coal, oil and gas burned since the Industrial Revolution in 1750 has caused the levels of <a href="https://www.co2.earth/">carbon dioxide in our atmosphere to rise</a> very significantly.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/UatUDnFmNTY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Time history of atmospheric carbon dioxide, by the Co-operative Institute for Research In Environmental Sciences (CIRES) and National Oceanic and Atmospheric Administration (NOAA)</span></figcaption>
</figure>
<p>Natural climate variations have continued to be a factor in Earth’s climate since the Industrial Revolution, but the rapid rise in carbon dioxide (and other greenhouse gases) has been the <a href="https://www.ipcc.ch/report/ar5/wg1/docs/WG1AR5_FAQbrochure_FINAL.pdf">dominant cause of climate warming during the industrial era</a>.</p>
<p>In 2016, the planet’s average surface temperature had risen to be about <a href="https://www.nasa.gov/press-release/nasa-noaa-data-show-2016-warmest-year-on-record-globally">1.1°C warmer than in the late 19th century</a>, when instrumental records began. This places our climate today at a similar global average temperature to the last interglacial.</p>
<hr>
<p><iframe id="tc-infographic-187" class="tc-infographic" height="2000" src="https://cdn.theconversation.com/infographics/187/6864d164de3795db8173059dc5a397f7e744e8fd/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<hr>
<p>When global average temperatures were 1-2°C warmer than pre-industrial times between 115,000 and 130,000 years ago, this caused so much of the Antarctic and Greenland ice sheets to destabilise and melt that <a href="http://science.sciencemag.org/content/349/6244/aaa4019">sea level rose by 6-9 metres</a>.</p>
<p>It takes time to melt an ice sheet. But in some parts of Antarctica, climate warming since the Industrial Revolution has <a href="https://theconversation.com/we-can-now-only-watch-as-west-antarcticas-ice-sheets-collapse-26957">already triggered unstoppable changes in the ice sheets</a> that will likely commit us to the higher end of the <a href="https://theconversation.com/what-does-the-science-really-say-about-sea-level-rise-56807">28-98cm range of sea-level rise</a> predicted for the end of this century by the latest report from the Intergovernmental Panel on Climate Change.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/157267/original/image-20170217-4280-742ine.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/157267/original/image-20170217-4280-742ine.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/157267/original/image-20170217-4280-742ine.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=432&fit=crop&dpr=1 600w, https://images.theconversation.com/files/157267/original/image-20170217-4280-742ine.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=432&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/157267/original/image-20170217-4280-742ine.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=432&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/157267/original/image-20170217-4280-742ine.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=543&fit=crop&dpr=1 754w, https://images.theconversation.com/files/157267/original/image-20170217-4280-742ine.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=543&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/157267/original/image-20170217-4280-742ine.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=543&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Peak global mean temperature, atmospheric CO2, maximum global mean sea level (GMSL), and source(s) of meltwater. Light blue shading indicates uncertainty of GMSL maximum. Red pie charts over Greenland and Antarctica denote fraction (not location) of ice retreat.</span>
<span class="attribution"><a class="source" href="http://science.sciencemag.org/content/349/6244/aaa4019">Dutton et al. Sea-level rise due to polar ice-sheet mass loss during past warm periods, Science.</a></span>
</figcaption>
</figure>
<h2>Verdict</h2>
<p>Senator Jacqui Lambie’s description of past climate change on Q&A was not entirely correct. </p>
<p>She was right to say that Earth’s climate has always changed. It always will - driven by a wide range of natural causes, and now dominated by the growing influence of human activities such as burning fossil fuels. And at different times it has been hotter and colder than today.</p>
<p>But was it 4°C hotter 110,000 years ago, as Lambie said? No, not globally. </p>
<p>The Antarctic was about 4°C hotter during last interglacial period (around 130,000-115,000 years ago) than it was in pre-industrial times – but the <em>global</em> average temperature then was closer to 1-2°C warmer than pre-industrial times. </p>
<p>Our climate today is at a similar global average temperature to the last interglacial period about 130,000-115,000 years ago. <strong>– Nerilie Abram</strong></p>
<h2>Review</h2>
<p>This is a sound FactCheck. It is presented in a clear and accessible manner. In drawing its conclusions it cites a range of peer-reviewed scientific literature in our top journals. It highlights the key distinction between local and global temperature, and our understanding of polar amplification. </p>
<p>I would only add that the rate of warming over the last century is very unusual in the context of glacial and interglacial cycles. When the earth has moved out of ice ages in recent millennia it has taken, <a href="http://earthobservatory.nasa.gov/Features/GlobalWarming/page3.php">on average, 1,000 years</a> to warm the planet by 1°C. The earth’s temperature in recent decades has risen at around <a href="http://earthobservatory.nasa.gov/Features/GlobalWarming/page3.php">1°C per 100 years</a>, or <a href="http://theconversation.com/meet-el-ninos-cranky-uncle-that-could-send-global-warming-into-hyperdrive-72360">faster</a>. So the recent <em>rate</em> of warming is very unusual in this context. NASA makes this point <a href="http://earthobservatory.nasa.gov/Features/GlobalWarming/page3.php">here</a>. </p>
<p>The climate science community is very well aware of the record of past changes in the Earth’s climate. Indeed, these changes are part of the evidence for why we expect the rapid accumulation of greenhouse gases in the atmosphere due to human activity to produce large changes to the climate. <strong>– Ben Henley</strong></p>
<hr>
<p><div class="callout"> Have you ever seen a “fact” worth checking? The Conversation’s FactCheck asks academic experts to test claims and see how true they are. We then ask a second academic to review an anonymous copy of the article. You can request a check at checkit@theconversation.edu.au. Please include the statement you would like us to check, the date it was made, and a link if possible.</div></p><img src="https://counter.theconversation.com/content/73045/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nerilie Abram receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Ben Henley receives funding from an ARC Linkage Project and is an associate investigator with the ARC Centre of Excellence for Climate System Science.</span></em></p>During a Q&A discussion about climate change, Tasmanian Senator Jacqui Lambie said it was four degrees hotter 110,000 years ago. Is that right?Nerilie Abram, ARC Future Fellow, Research School of Earth Sciences; Chief Investigator for the ARC Centre of Excellence for Climate Extremes, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/591652016-05-10T20:19:55Z2016-05-10T20:19:55ZAntarctic ice shows Australia’s drought and flood risk is worse than thought<figure><img src="https://images.theconversation.com/files/121846/original/image-20160510-20721-7yi8c1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The past century hasn't seen the worst drought that Australia's climate can throw at us.</span> <span class="attribution"><span class="source">CSIRO/Wikimedia Commons</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Australia is systematically underestimating its drought and flood risk because weather records do not capture the full extent of rainfall variability, according to our new research.</p>
<p>Our <a href="http://www.hydrol-earth-syst-sci.net/20/1703/2016">study</a>, published today in the journal Hydrology and Earth System Sciences, uses Antarctic ice core data to reconstruct rainfall for the past 1,000 years for catchments in eastern Australia. </p>
<p>The results show that instrumental rainfall records – available for the past 100 years at best, depending on location – do not represent the full range of abnormally wet and dry periods that have occurred over the centuries. </p>
<p>In other words, significantly longer and more frequent wet and dry periods were experienced in the pre-instrumental period (that is, before the 20th century) compared with the period over which records have been kept. </p>
<h2>Reconstructing prehistoric rainfall</h2>
<p>There is no direct indicator of rainfall patterns for Australia before weather observations began. But, strange as it may sound, there is a link between eastern Australian rainfall and the summer deposition of sea salt in Antarctic ice. This allowed us to deduce rainfall levels by studying ice cores drilled from Law Dome, a small coastal ice cap in East Antarctica. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/121856/original/image-20160510-20734-1uboyt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/121856/original/image-20160510-20734-1uboyt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/121856/original/image-20160510-20734-1uboyt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/121856/original/image-20160510-20734-1uboyt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/121856/original/image-20160510-20734-1uboyt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/121856/original/image-20160510-20734-1uboyt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/121856/original/image-20160510-20734-1uboyt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/121856/original/image-20160510-20734-1uboyt.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"></a>
<figcaption>
<span class="caption">It might sound strange, but there’s a direct link between Antarctic ice and Australia’s rainfall patterns.</span>
<span class="attribution"><span class="source">Tas van Ommen</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>How can sea salt deposits in an Antarctic ice core possibly be related to rainfall thousands of kilometres away in Australia? It is because the processes associated with rainfall variability in eastern Australia – such as the El Niño/Southern Oscillation (ENSO), as well as other ocean cycles like the Interdecadal Pacific Oscillation (IPO) and the Southern Annular Mode (SAM) – are also responsible for variations in the wind and circulation patterns that cause sea salt to be deposited in East Antarctica (as outlined in our <a href="http://onlinelibrary.wiley.com/doi/10.1002/2014GL062447/abstract">previous</a> <a href="http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00003.1">research</a>).</p>
<p>By studying an ice record spanning 1,013 years, our results reveal a clear story of wetter wet periods and drier dry periods than is evident in Australia’s much shorter instrumental weather record. </p>
<p>For example, in the Williams River catchment, which provides water for the Newcastle region of New South Wales, our results showed that the longest dry periods lasted up to 12 years. In contrast, the longest dry spell since 1900 lasted just eight years. </p>
<p>Among wet periods, the difference was even more pronounced. The longest unusually wet spell in our ice record lasted 39 years – almost five times longer than the post-1900 maximum of eight years.</p>
<h2>Busting myths about drought and flood risk</h2>
<p>Although this does not tell us when the next major wet or dry period will happen, it does help us predict how often we can expect such events to occur, and how long they might last. This is critical information for water resource managers and planners, especially when our millennium-long record tells a very different story to the post-1900 instrumental record on which all water infrastructure, planning and policy is based.</p>
<p>Our results challenge the underlying assumptions that govern water resource management and infrastructure planning. These assumptions include: </p>
<ul>
<li><p>that droughts longer than five years are rare; </p></li>
<li><p>that droughts or flood-dominated periods cannot last longer than about 15 years;</p></li>
<li><p>that drought and flood risk does not change over time, so a century of instrumental records is enough to gain a full understanding of the situation. </p></li>
</ul>
<p>The fact that these assumptions are probably wrong is a concern. These principles are used to make crucial decisions, not just about predicting the likelihood and severity of droughts and floods themselves, but also about the design of infrastructure such as roads, reservoirs and buildings. Our study suggests that these decisions are being taken on the basis of incomplete information.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/121857/original/image-20160510-20731-9cwepy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/121857/original/image-20160510-20731-9cwepy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/121857/original/image-20160510-20731-9cwepy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/121857/original/image-20160510-20731-9cwepy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/121857/original/image-20160510-20731-9cwepy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/121857/original/image-20160510-20731-9cwepy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/121857/original/image-20160510-20731-9cwepy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/121857/original/image-20160510-20731-9cwepy.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">Cold case: drilling for ice to reveal long-term weather patterns.</span>
<span class="attribution"><span class="source">Tessa Vance</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>What’s more, Australia’s increasing population and development will mean that water demands and exposure to droughts and floods are likely to have been different in the past to what they are now (and will be in the future). </p>
<p>Therefore, given that the factors used to quantify risk are most likely wrong, it implies that current hydroclimatic risk assessments are not representative of the true level of risk. </p>
<p>This raises serious questions about water security and the robustness of existing water resource management, infrastructure design and catchment planning across eastern Australia and in other places where hydroclimatic risk is assessed on records that do not capture the full range of possible variation.</p>
<p>Water is a precious resource, meaning that we need the best knowledge about what our rainfall patterns are capable of delivering. Our findings can be used to better characterise and manage existing and future flood and drought risk. Forewarned is forearmed.</p><img src="https://counter.theconversation.com/content/59165/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Anthony Kiem receives funding from the Australian Research Council. Anthony does not work for or own shares in any company or organization that would benefit from this article. </span></em></p><p class="fine-print"><em><span>Carly Tozer receives funding from the Antarctic Climate & Ecosystems CRC (based at the University of Tasmania) and the University of Newcastle. </span></em></p><p class="fine-print"><em><span>Tessa Vance receives funding from the federal government through the Antarctic Climate & Ecosystems CRC (based at the University of Tasmania). She receives logistical and project support from the Australian Antarctic Division. </span></em></p>A new millennium-long record reveals that Australia has suffered longer droughts and wet periods than those recorded in the past century’s weather observations.Anthony Kiem, Senior Lecturer – Hydroclimatology, University of NewcastleCarly Tozer, Hydrologist, Antarctic Climate & Ecosystems Cooperative Research Centre, University of Tasmania, University of NewcastleTessa Vance, Palaeoclimatologist, Antarctic Climate & Ecosystems Cooperative Research Centre, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/552352016-03-07T03:27:31Z2016-03-07T03:27:31ZChasing ice: how ice cores shape our understanding of ancient climate<figure><img src="https://images.theconversation.com/files/113976/original/image-20160307-3860-stj5n5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Million-year-old ice likely lies more than 3km below Antarctica's surface. </span> <span class="attribution"><span class="source">Tas van Ommen</span>, <span class="license">Author provided</span></span></figcaption></figure><p>It is just over 50 years since French scientist Claude Lorius dropped some glacier ice in his whisky and started a quest that continues today. Lorius was studying glaciers in Antarctica and wondered if the air bubbling out of some ice he had drilled that day might carry information from the past. </p>
<p>The answer to that question was “yes”. We now know that <a href="https://theconversation.com/explainer-what-are-ice-cores-24302">ice cores carry a rich archive of past information</a> in the bubbles and the ice itself. </p>
<p>This week the <a href="http://www.ipics2016.org/">world’s ice core community is meeting in Hobart</a> as the 24 nations of the International Partnerships in Ice Core Sciences (IPICS) gather. IPICS was formed in 2004 to help coordinate and guide this highly collaborative branch of science. Large ice-coring projects involve challenging logistics in the harshest environments on earth, so well-developed and coordinated programs are important.</p>
<h2>Secrets in the ice</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/113341/original/image-20160301-4063-1n4dcmf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/113341/original/image-20160301-4063-1n4dcmf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/113341/original/image-20160301-4063-1n4dcmf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/113341/original/image-20160301-4063-1n4dcmf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/113341/original/image-20160301-4063-1n4dcmf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/113341/original/image-20160301-4063-1n4dcmf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/113341/original/image-20160301-4063-1n4dcmf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/113341/original/image-20160301-4063-1n4dcmf.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"></a>
<figcaption>
<span class="caption">Drilling ice.</span>
<span class="attribution"><span class="source">Tas van Ommen</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The field of ice core palaeoclimate is now a mature branch of earth science that has provided revolutionary insights into the climate of the past 800,000 years. No insight is more potent than the revelation that global temperature and carbon dioxide (CO<sub>2</sub>) <a href="https://www.bas.ac.uk/wp-content/uploads/2015/04/003.jpg">march in lock step</a> through the ice ages. Current CO<sub>2</sub> levels sit far above the natural range (now just over 400 parts per million (ppm), or more than 100 ppm higher than any time in 800,000 years).</p>
<p>Drilling an ice core is a significant logistical exercise. It can take several years of preparation, and for deep cores (1km to over 3km deep) requires several summer seasons in the field to drill. Shallower cores, up to several hundred metres in depth, can be drilled in a single field season, so it is possible to build up a broader array of these cores across Antarctica. </p>
<p>Over the years a number of long, deep ice core records have been extracted from Antarctica and Greenland, along with many shorter cores from polar and mountain glaciers around the world. There is a pressing need to continue the work. Ever-improving analytical methods are delivering more information from ice cores more efficiently, but there are still too few core sites to build a reliable picture of past change. </p>
<p>For example, recent research to <a href="http://www.nature.com/ngeo/journal/v6/n5/full/ngeo1797.html">reconstruct the climate for the last 2,000 years</a> relied on just four cores in East Antarctica: a challenge comparable to understanding Australia’s climate from just four or five weather stations.</p>
<p>As we seek to mitigate the worst impacts of climate change and adapt to inevitable changes, it is critical to understand how the climate system behaves in the longer term.</p>
<h2>Looking to the future</h2>
<p>We know which questions we need to answer first. At the most basic level, we need to expand our network of ice cores so that we can better study climate variations over the last couple of millennia.</p>
<p>This work has proved important for testing climate models. We can use information from ice cores to see how accurately climate models recreate past climates, which helps us assess how useful they are for predicting the future. For Australia, ice cores have expanded our understanding of <a href="http://www.antarctica.gov.au/news/2014/antarctic-ice-cores-tell-1000-year-australian-drought-story">factors influencing drought</a>.</p>
<p>The most ambitious priority for ice core science is the challenge of recovering a core that extends to well over a million years ago. The oldest ice core presently reaches just 800,000 years, but there is a strong prospect that ice over a million years old exists near the bottom of the Antarctic icecap (more than 3km below the surface). </p>
<p>Around a million years ago, ice age cycles shifted their pacing from 41,000 years’ to 100,000 years’ length. We don’t know what caused this shift. An ice core covering this period would allow us to extract a direct record of CO<sub>2</sub> and see what role, if any, it may have played.</p>
<p>Another challenge that requires a major deep drilling effort is to explore the warm period before the last ice age began, around 100,000 years ago. This warm period, or interglacial, peaked around 2˚C warmer than pre-industrial times. Sea levels then were 6-9 metres above present. </p>
<p>New ice core records from Greenland and Antarctica would help to understand how fast sea levels rose and how the pattern and timing of warming varied across the planet. At the moment, the Greenland ice core records of this period are discontinuous and incomplete, while Antarctica offers the prospect of very detailed ice cores that tell more about the size of the Antarctic ice sheet through this period of higher sea level.</p>
<p>Such information would be valuable in understanding the rates and extent of sea level rise that face us in the future.</p>
<p>Ice core scientists are also looking to projects that might help us understand complexities of ice flow as well as purely climatic information. These could drive new drilling in challenging places like ice streams. </p>
<p>A further pressing issue that is being discussed is the rapid loss of icecaps in mountainous regions. These vanishing glaciers hold climate information that will soon be lost to us, so the ice core community is urgently looking to drill and <a href="http://phys.org/news/2015-03-ice-vault-idea-climate-capsule.html">archive this precious resource</a>.</p><img src="https://counter.theconversation.com/content/55235/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tas van Ommen is a national delegate to the International Partnerships in Ice Core Sciences. </span></em></p>Ice cores tell us vital information about how the world’s climate has changed - and how it will change in the future.Tas van Ommen, Senior Principal Research Scientist - Climate and Ice, Australian Antarctic DivisionLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/243022014-03-20T06:09:38Z2014-03-20T06:09:38ZExplainer: what are ice cores?<figure><img src="https://images.theconversation.com/files/43731/original/g6n7yw5v-1394637688.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ice core samples storing mysteries from bygone eras. </span> <span class="attribution"><a class="source" href="http://www.flickr.com/photos/genericprofilename/7009543197/in/photostream/">Genericprofilename</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Ice cores are cylinders of ice drilled from glaciers and ice sheets. When snow falls it takes with it a record of many aspects of the atmosphere. As long as no melting takes place, this information is preserved as each layer of snow is buried by successive snowfalls from year to year. By drilling into the ice sheet, we can recover a chronological archive of the atmosphere.</p>
<p>Most ice cores are recovered from the Greenland and Antarctic ice sheets. However, it is also possible to obtain cores from glaciers at high altitudes at lower latitudes for example, in the Alps, Andes and Himalaya mountains. In the two large polar ice sheets, the ice may be more than 3000m deep. </p>
<p>Cores are recovered using drills that collect typically 3m of ice at a time, in a cylinder often 10cm in diameter. The drill is on the end of a cable: it is lowered to the depth of the previous collection, where it grips the side of the hole so that an inner section, with drill teeth on the lower end, can rotate. The teeth cut a ring of chippings, so that a cylinder of ice fills the inside of the drill barrel. This is then taken to the surface. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/43830/original/j643z4cx-1394696342.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/43830/original/j643z4cx-1394696342.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=915&fit=crop&dpr=1 600w, https://images.theconversation.com/files/43830/original/j643z4cx-1394696342.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=915&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/43830/original/j643z4cx-1394696342.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=915&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/43830/original/j643z4cx-1394696342.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1149&fit=crop&dpr=1 754w, https://images.theconversation.com/files/43830/original/j643z4cx-1394696342.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1149&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/43830/original/j643z4cx-1394696342.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1149&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Drilling an ice core.</span>
<span class="attribution"><span class="source">R Mulvaney/British Antarctic Survey</span></span>
</figcaption>
</figure>
<p>Because ice deforms under pressure, the hole has to be filled with an inert fluid that keeps it from closing. The ice cores are then kept cold, in insulated boxes inside freezers, while they are transported from Greenland and Antarctica to laboratories of universities and research institutes for analysis.</p>
<h2>Analysing the ice</h2>
<p>The ice can be dated by various methods – in favourable cases it is possible to find a chemical whose concentration varies from summer to winter, so that each year can be counted. However often more complex methods are used to determine the age. The oldest ice recovered in an ice core so far is <a href="http://www.sciencemag.org/content/317/5839/793.abstract">800,000 years in Antarctica and 128,000 years in Greenland</a>.</p>
<p>The ice can be analysed for its physical properties (such as electrical conductivity), and sections are melted for chemical analysis. Information is held in three forms:</p>
<ol>
<li><p>The water molecules of the ice itself are not all the same – they come in various isotopic forms. The ratio between the different isotopes is used to determine the temperature at the time the snow fell.</p></li>
<li><p>Various chemicals are trapped with the snow at the surface of the ice sheet. For example, after large volcanic eruptions, sulfuric acid is deposited from the atmosphere and shows up in ice cores as clear spikes in sulfate concentration against a relatively flat background. </p></li>
<li><p>As the layers of snow are buried the individual crystals of snow eventually (at somewhere between 60 and 100m deep) join together to form a solid matrix of ice with air bubbles trapped inside. These air bubbles contain a sample of all the stable gases in the air from the time that it compacted including nitrogen, oxygen and argon. They can be cracked open for analysis. </p></li>
</ol>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/43829/original/pkx2gmt2-1394696336.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/43829/original/pkx2gmt2-1394696336.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=394&fit=crop&dpr=1 600w, https://images.theconversation.com/files/43829/original/pkx2gmt2-1394696336.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=394&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/43829/original/pkx2gmt2-1394696336.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=394&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/43829/original/pkx2gmt2-1394696336.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=495&fit=crop&dpr=1 754w, https://images.theconversation.com/files/43829/original/pkx2gmt2-1394696336.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=495&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/43829/original/pkx2gmt2-1394696336.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=495&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Air bubbles in an ice core.</span>
<span class="attribution"><span class="source">British Antarctic Survey</span></span>
</figcaption>
</figure>
<h2>Unlocking knowledge of the past</h2>
<p>Ice cores are a very important source of information about the past. They are the main archive of information about temperature and snowfall rates in the polar regions, as well as our only direct record of atmospheric composition <a href="http://pubs.rsc.org/en/Content/ArticleLanding/2012/CS/c2cs35227c#!divAbstract">before the middle of the 20th century</a>.</p>
<p>Numerous chemicals can be measured that give information about the extent of past sea ice, volcanic activity, the strength of the sun, winds and many other environmental parameters. Information from ice cores is then complemented by other palaeoclimate archives such as marine sediments, corals, tree rings and speleothems (mineral deposits that form in caves such as stalactites).</p>
<p>Numerous major scientific findings have emerged from ice cores. Carbon dioxide concentrations were fairly steady at around 280 parts per million in the millenium before 1800, but have risen to nearly <a href="dx.doi.org/10.1029/2006GL026152">400 parts per million since then</a>. This reveals the extent that industrialisation has added CO<sub>2</sub> to the atmosphere, and clarifies how unusual recent changes are compared to the small and slow natural variations throughout history.</p>
<p>At a much longer timescale, Antarctic ice cores have shown that temperatures there, like many other climate signals, varied between warm interglacial periods and cold “ice ages” roughly every 100,000 years. Carbon dioxide concentrations in the ice tracked faithfully with the temperature changes. The CO<sub>2</sub> increases at the end of each cold period helped to amplify small regional changes in climate into the large global changes that led Earth into and out of ice ages.</p>
<p>Ice cores therefore play an important role in adding to our understanding of the Earth’s climate through the ages and help us confirm and map how the climate has evolved. Unfortunately they don’t give much of a forecast for the future, however, because the ice core era does not contain concentrations of CO<sub>2</sub> comparable to now and the future.</p><img src="https://counter.theconversation.com/content/24302/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Eric W. Wolff has received funding from the Natural Environment Research Council (UK), the Royal Society and the European Union (under FP7).</span></em></p>Ice cores are cylinders of ice drilled from glaciers and ice sheets. When snow falls it takes with it a record of many aspects of the atmosphere. As long as no melting takes place, this information is…Eric W. Wolff, Royal Society Research Professor of Earth Sciences, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/235762014-02-25T05:58:54Z2014-02-25T05:58:54ZStudying Earth’s distant past can teach us lessons about its climate for the future<figure><img src="https://images.theconversation.com/files/42386/original/w2qwx7jc-1393268101.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The past, on ice.</span> <span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:NICL_Freezer.jpg">National Ice Core Lab</a></span></figcaption></figure><p>How can air bubbles trapped in ice for millions of years, or fossilised fern fronds, or the chemical make-up of rocks that were underwater in the distant past provide us with an inkling of our future?</p>
<p>The answer lies in these clues provided by studying the <a href="http://www.bbc.co.uk/nature/history_of_the_earth/Pliocene">Pliocene epoch</a>, the span of geological time that stretched from 5.3 to 2.6 million years ago. This period of Earth’s history is interesting for many reasons, but one of the most profound is that the Earth’s atmosphere apparently contained high concentrations of carbon dioxide. Our best estimates suggest concentrations of about <a href="http://env.lowtem.hokudai.ac.jp/saishin.pdf/Seki2010EarthPlanetarySci.Lett.Alkenone%20and%20boran-based%20Plicene%20pCO2%20records.pdf">300-400 parts per million</a> (ppm) – much higher than concentrations of 100 years ago, but <a href="http://co2now.org/">the same or lower than today</a> after centuries of industrialisation and fossil fuel burning.</p>
<p>So studying the Pliocene could provide valuable insight into the type of planet we are creating via global warming. Our researchers at the Cabot Institute recently released a <a href="http://www.youtube.com/watch?v=KpLvPT5a6jg'">video</a> on the topic, which has coincided with pronounced flooding across the UK and renewed attention focused on our weather and climate. There is little doubt that increased carbon dioxide concentrations will cause global warming. The key questions are <a href="https://www.ipcc.ch/report/ar5/wg1/docs/review/WG1AR5-SPM_FOD_Final.pdf">how much, and with what consequences</a>.</p>
<p>One of the key lessons from Earth history is <a href="http://www.scientificamerican.com/article/ipcc-revises-climate-sensitivity/">climate sensitivity</a>. Climate sensitivity can be expressed in various ways, but in its simplest sense it is a measure of how much warmer the Earth becomes for a given doubling of atmospheric carbon dioxide concentrations.</p>
<p>This is well known for the <a href="https://www.skepticalscience.com/hansen-and-sato-2012-climate-sensitivity.html">Pleistocene</a>, and especially the past 800,000 years of Earth history, a period for which we have detailed temperature reconstructions and carbon dioxide records derived from bubbles of gas trapped in ancient ice cores. </p>
<p>During that time, across several ice ages, the planet’s climate sensitivity showed warming of about 2.5-3°C for a doubling of carbon dioxide, which falls in the middle of the range of predictions given by models. Ice core records, however, extend back no more than a million years, and this time period is generally characterised by colder climates than those of today. If we want to explore climate sensitivity on a warmer planet, we must look further back into Earth history, to times such as the Pliocene.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/KpLvPT5a6jg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Reconstructing atmospheric carbon dioxide concentrations without relying on ice cores is admittedly more challenging. Instead of directly measuring the concentration of carbon dioxide in gas bubbles, we must rely on indirect records. For example, carbon dioxide concentration influences the number of stomata (pores) on plant leaves, and this can be measured on the fossils of ancient leaves. Alternatively, there are a number of geochemical tools based on how carbon dioxide affects the pH of seawater, or how algae take up carbon dioxide as they photosynthesise – these are recorded in the chemical composition of ancient fossils.</p>
<p>These means of drawing estimates come with larger margins of error, but they still provide key insights into climate sensitivity on a warmer Earth. Recent <a href="http://env.lowtem.hokudai.ac.jp/saishin.pdf/Seki2010EarthPlanetarySci.Lett.Alkenone%20and%20boran-based%20Plicene%20pCO2%20records.pdf">research</a> indicates that these various carbon dioxide estimates of Pliocene carbon dioxide levels are converging, giving added confidence from which to derive estimates of climate sensitivity. In particular, it seems an increase of carbon dioxide from about 280ppm (equivalent to that before the industrial revolution) to about 400ppm in the Pliocene resulted in an Earth <a href="http://geology.er.usgs.gov/eespteam/prism/prism_gallery.html">warmer by 2°C</a>.</p>
<p>Taking into account other factors, this suggests a climate sensitivity of about 3°C, which confirms both the Pleistocene and model-based estimates. It also suggests that we have yet to experience the full consequences of the greenhouse gases already added to the atmosphere, let alone those we are still putting into it.</p>
<p>So then, what was this much warmer world like? First of all, it was not an inhospitable planet – plants and animals thrived. This should not be a surprise – in fact, the Earth was much warmer <a href="http://onlinelibrary.wiley.com/doi/10.1002/2013GC004935/abstract">even further back into the past</a>. The changes in the climate we are inducing is a problem for us humans, and for our societies, not the planet we’re on. However, the Pliocene was a rather different world. For example – relevant considering current events in Britain – higher global temperatures <a href="http://www.ncbi.nlm.nih.gov/pubmed/18854302">were associated</a> with a climate that was also <a href="https://www.sciencemag.org/content/340/6139/1421.abstract">wetter than at present</a>. That provides important corroborating evidence for models that predict <a href="http://www.metoffice.gov.uk/media/pdf/1/2/Recent_Storms_Briefing_Final_SLR_20140211.pdf">a warmer and wetter future</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/42387/original/9hmgybnt-1393268376.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/42387/original/9hmgybnt-1393268376.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=67&fit=crop&dpr=1 600w, https://images.theconversation.com/files/42387/original/9hmgybnt-1393268376.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=67&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/42387/original/9hmgybnt-1393268376.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=67&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/42387/original/9hmgybnt-1393268376.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=84&fit=crop&dpr=1 754w, https://images.theconversation.com/files/42387/original/9hmgybnt-1393268376.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=84&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/42387/original/9hmgybnt-1393268376.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=84&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A section of an ice core of from 16,000 years ago.</span>
<span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:GISP2D1837_crop.jpg">National Ice Core Laboratory</a></span>
</figcaption>
</figure>
<p>Perhaps most striking, sea level appears to have been between <a href="http://www.nature.com/ngeo/journal/v4/n5/full/ngeo1118.html">10 to 40 metres</a> higher than today, indicating that both the Greenland Ice Sheet and Antarctic Ice Sheet were markedly smaller. To put that into context, the Met Office has already commented on how flooding in the UK has been affected by sea level rise <a href="http://www.metoffice.gov.uk/media/pdf/1/2/Recent_Storms_Briefing_Final_SLR_20140211.pdf">of 12cm over the last 100 years</a>, and will be exacerbated further by another 5-7cm by 2030.</p>
<p>We must be careful in how we extract climate lessons from the geological record, and that is particularly true when we consider ice sheet behaviour. One widely discussed concept is <a href="https://www.geo.umass.edu/climate/papers2/pollard_deconto_hysteresis.pdf">ice sheet hysteresis</a>. This is a fancy way of saying that due to feedback mechanisms, it could be easier to build an ice sheet on Greenland or Antarctica than it is to melt one. If hysteresis is a force stabilising our current ice sheets, then it may be that a planet with today’s carbon dioxide levels of 400 ppm will not necessarily have a sea level 20 metres higher than that of today – as it was during the Pliocene. On the other hand if hysteresis is rather weak, then the question is not whether we will see such a massive sea level change, but how long it will take to arrive (probably hundreds or even thousands of years).</p>
<p>Most importantly, the collective research into Earth history, including the Pliocene, reveals that Earth’s climate can and has changed. It also reveals that climate does not just change randomly: it changes when forced in ways that are relatively well understood – one of these is the concentration of carbon dioxide in our atmosphere. And consequently, there is little doubt from Earth’s history that transforming fossil carbon underground into carbon dioxide in the air – as we are doing today – will significantly affect the climate we experience for the forseeable future.</p>
<p><em>Professor Rich Pancost gives a public lecture on how biogeochemical cycles have regulated the global climate system throughout Earth’s history today, February 25th, in Bristol. The event is free and <a href="http://bristol.ac.uk/cabot/events/2014/375.html">open to all</a>.</em></p><img src="https://counter.theconversation.com/content/23576/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Richard Pancost receives funding from the RCUK (NERC) to support this research.</span></em></p>How can air bubbles trapped in ice for millions of years, or fossilised fern fronds, or the chemical make-up of rocks that were underwater in the distant past provide us with an inkling of our future…Richard Pancost, Professor of Biogeochemistry, Director of the Cabot Institute, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/99412012-10-28T13:12:35Z2012-10-28T13:12:35ZHumans did affect the atmosphere - even before industrialisation<figure><img src="https://images.theconversation.com/files/16701/original/dghqhc8n-1350602040.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">By studying ice cores, researchers can measure the methane emissions from thousands of years earlier.</span> <span class="attribution"><span class="source">Arabani/Flickr</span></span></figcaption></figure><p>The past is the key to the future. When snow falls on polar ice sheets, in Greenland and Antarctica for example, air is trapped between the snowflakes. Year after year, the snow compacts under its own weight to become ice, and air is enclosed in small bubbles. These are the best atmospheric archives on Earth. </p>
<p>By analysing the air enclosed in polar ice, we can reconstruct past changes in the atmosphere’s composition. We have reconstructed past methane (CH<sub>4</sub>) variations back to the Roman Empire period, and discovered that humans emitted significant amounts of methane 2,000 years ago.</p>
<p>Nobel Prize winner in chemistry <a href="http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1995/crutzen-autobio.html">Paul Crutzen</a> described the current geological period as the “Anthropocene”, or the human era. It started with the onset of the industrial revolution in the second half of the 19th century, when human-related emissions of atmospheric trace gases strongly increased. </p>
<p>But did it really start then? For how long have humans influenced the composition of the atmosphere? </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/16879/original/9nxhsjw9-1351128867.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/16879/original/9nxhsjw9-1351128867.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=392&fit=crop&dpr=1 600w, https://images.theconversation.com/files/16879/original/9nxhsjw9-1351128867.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=392&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/16879/original/9nxhsjw9-1351128867.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=392&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/16879/original/9nxhsjw9-1351128867.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=492&fit=crop&dpr=1 754w, https://images.theconversation.com/files/16879/original/9nxhsjw9-1351128867.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=492&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/16879/original/9nxhsjw9-1351128867.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=492&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Freshly drilled ice core used in the research.</span>
<span class="attribution"><span class="source">Supplied</span></span>
</figcaption>
</figure>
<p>A decade ago, famous climatologist <a href="http://www.evsc.virginia.edu/faculty/ruddiman-william-f/">William Ruddiman</a> suggested humans influenced the climate much earlier than previously thought. Ruddiman’s hypothesis was criticised, but a few years later <a href="http://www.sciencemag.org/content/309/5741/1714.abstract">isotope measurements</a> on methane trapped in polar ice cores indicated strong biomass burning - likely related to human activity - had increased atmospheric methane levels <a href="http://www.fas.harvard.edu/%7Eeps5/writing_assignment/T_GHG_RECON/Ferretti2005.pdf">before the 16th century</a>.</p>
<p>The strength of isotope measurements is that they allow distinguishing variations in methane emitted from various sources. Indeed, every type of sources produces methane with a characteristic isotopic signature.</p>
<p>Because methane is emitted by multiple sources, understanding its budget is not straightforward. These sources can be divided into three categories: biogenic, pyrogenic and fossil sources, with each category comprising both natural and anthropogenic methane emissions.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/16702/original/xb8t4vt7-1350602056.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/16702/original/xb8t4vt7-1350602056.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=428&fit=crop&dpr=1 600w, https://images.theconversation.com/files/16702/original/xb8t4vt7-1350602056.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=428&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/16702/original/xb8t4vt7-1350602056.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=428&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/16702/original/xb8t4vt7-1350602056.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=538&fit=crop&dpr=1 754w, https://images.theconversation.com/files/16702/original/xb8t4vt7-1350602056.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=538&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/16702/original/xb8t4vt7-1350602056.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=538&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Rice paddies have been a source of biogenic methane for thousands of years.</span>
<span class="attribution"><span class="source">Chericbaker/Flickr</span></span>
</figcaption>
</figure>
<p>Biogenic methane is formed by tropical and boreal wetlands, ruminants, rice paddies, landfills and waste water treatment. Pyrogenic emissions include biomass burning and the combustion of bio fuel. And fossil sources can be divided into two groups: fossil fuel and geological sources (methane formed deep in the Earth’s crust, which then travels upward through the sediment to the atmosphere).</p>
<p>In order to better understand the contribution of the different methane sources to the atmospheric burden, we have analysed the methane isotopic signature on ice core samples from Greenland. These samples date back to the Roman empire period.</p>
<p>Our results were interpreted with the help of atmospheric models. They show that the centennial-scale variations in isotope ratios can be attributed to changes in pyrogenic and biogenic sources. They also reveal several distinct periods of higher methane emissions from biomass burning within the last two thousand years. </p>
<p>Variations in biomass burning coincided partly with climate variability (changes in temperature and precipitation), but also with changes in human population and land use. For example, the burning-related emissions decreased during the decline of the Roman empire and the Han dynasty, and increased during the population expansion of the Medieval period. This is attributed to increased deforestation during those periods, but also to the burning of wood for heating purposes and metallurgy. </p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/16454/original/m2fs4nyq-1350007639.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/16454/original/m2fs4nyq-1350007639.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/16454/original/m2fs4nyq-1350007639.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/16454/original/m2fs4nyq-1350007639.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/16454/original/m2fs4nyq-1350007639.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/16454/original/m2fs4nyq-1350007639.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/16454/original/m2fs4nyq-1350007639.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">The construction of armour in medieval periods also affected the Earth’s atmosphere.</span>
<span class="attribution"><span class="source">DavidInc/Flick</span></span>
</figcaption>
</figure>
<p>Heavy metals in dust were recorded in the sediment of several lakes in Asia and in Greenland ice. This shows metallurgy, especially to produce weapons and tools, was important during these periods.</p>
<p>Further analysis of changes in land use was carried out by <a href="http://arve.epfl.ch/">EPFL’s Atmosphere Regolith Vegetation</a> group in Lausanne, Switzerland. Their results, together with the methane data, suggest that the long-term increase in methane concentration over the last two thousand years is caused at least partly by agricultural activities. For example, the development of rice paddies and irrigation of agricultural fields, thereby providing experimental evidence for the Ruddiman hypothesis.</p>
<p>It seems humans had a global impact on the atmosphere long before industrialisation. The results of our study show a need to reconsider the benchmark of natural versus “anthropogenic” eras, while aiming to predict future climates. </p><img src="https://counter.theconversation.com/content/9941/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Célia Sapart is affiliated with Institute for Marine and Atmospheric Research Utrecht, Utrecht Universtity, The Netherlands.</span></em></p>The past is the key to the future. When snow falls on polar ice sheets, in Greenland and Antarctica for example, air is trapped between the snowflakes. Year after year, the snow compacts under its own…Célia Sapart, Postdoctoral Researcher, Atmospheric Physics and Chemistry Group, Utrecht UniversityLicensed as Creative Commons – attribution, no derivatives.