tag:theconversation.com,2011:/global/topics/james-hansen-18908/articlesJames Hansen – The Conversation2023-12-08T16:37:43Ztag:theconversation.com,2011:article/2177592023-12-08T16:37:43Z2023-12-08T16:37:43ZThe disagreement between two climate scientists that will decide our future<figure><img src="https://images.theconversation.com/files/564531/original/file-20231208-25-i2uuog.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2700%2C1797&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/earth-observation-outer-space-elements-this-544968547">Vladi333/Shutterstock</a></span></figcaption></figure><p>Getting to net zero emissions by mid-century is conventionally understood as humanity’s best hope for keeping Earth’s surface temperature (already 1.2°C above its pre-industrial level) from increasing well beyond 1.5°C – potentially reaching a point at which it could cause widespread societal breakdown. </p>
<p>At least one prominent climate scientist, however, disagrees. </p>
<p>James Hansen of Columbia University in the US published <a href="https://academic.oup.com/oocc/article/3/1/kgad008/7335889?searchresult=1">a paper</a> with colleagues in November which claims temperatures are set to rise further and faster than the predictions of the Intergovernmental Panel on Climate Change (IPCC). <a href="https://www.youtube.com/watch?v=NXDWpBlPCY8">In his view</a>, the 1.5°C target is dead. </p>
<p>He also claims net zero is no longer sufficient to prevent warming of more than 2°C. To regain some control over Earth’s rising temperature, Hansen supports accelerating the retirement of fossil fuels, greater cooperation between major polluters that accommodates the needs of the developing world and, controversially, intervening in Earth’s “<a href="https://theconversation.com/why-dimming-the-sun-would-be-an-effective-tool-in-the-fight-against-climate-change-218670">radiation balance</a>” (the difference between incoming and outgoing light and heat) to cool the planet’s surface. </p>
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<p>There would probably be wide support for the first two prescriptions. But Hansen’s support for what amounts to the deliberate reduction of sunlight reaching Earth’s surface has brought into the open an idea that makes many uncomfortable. </p>
<p>Michael Mann from the University of Pennsylvania in the US and another <a href="https://www.scientificamerican.com/article/behind-the-hockey-stick/">titan of climate science</a>, spoke for many when he <a href="https://michaelmann.net/content/comments-new-article-james-hansen">dismissed solar radiation management</a> as “potentially very dangerous” and a “desperate action” motivated by the “fallacy … that large-scale warming will be substantially greater than current-generation models project”. </p>
<p>Their positions are irreconcilable. So who is right – Hansen or Mann?</p>
<h2>Earth’s radiation balance</h2>
<p>First, an explanation. </p>
<p>There are only two ways to reduce global warming. One is to increase the amount of heat radiated from Earth’s surface that escapes to space. The other is to increase the amount of sunlight reflected back to space before it lands on something – whether a particle in the atmosphere or something on Earth’s surface – and is converted to heat.</p>
<p>There are many ways to do both. Anything that reduces the amount of greenhouse gas in the atmosphere will let more heat escape to space (replacing fossil fuels with renewables, eating less meat and tilling the soil less for example). Anything that makes the planet brighter will reflect more sunlight to space (such as refreezing the Arctic, making clouds whiter or putting more reflective particles in the atmosphere). </p>
<p>But the key difference between the two, in terms of their impact on global warming, is their response time. That is, the time it takes for a change in the factors that allow more heat to escape or sunlight to be reflected to appear as a change in Earth’s surface temperature. </p>
<p>Intervening to speed up the loss of heat from Earth’s surface cools the planet slowly, over decades and longer. Intervening to increase the sunlight Earth reflects back to space cools the planet more or less immediately. </p>
<p>The essence of the dispute between Mann and Hansen is whether reducing greenhouse gases, by a combination of reducing new emissions and permanently removing past emissions from the atmosphere, is now enough on its own to prevent warming from reaching levels that threaten economic and social stability.</p>
<p>Mann says it is. Hansen says that, while doing these things remains essential, it is no longer sufficient and we must also make Earth more reflective.</p>
<h2>When will warming end?</h2>
<p>Mann aligns with IPCC orthodoxy when he says that emissions reaching net zero will result, within a decade or two, in Earth’s surface temperature stabilising at the level it has then reached. </p>
<p>In effect, there is no significant warming in the pipeline from past emissions. All future warming will be due to future emissions. This is the basis for the global policy imperative to get to net zero.</p>
<p>In his new paper, Hansen argues that if the atmospheric concentration of greenhouse gases remains close to its current level, the surface temperature will stabilise after several hundred years between 8°C and 10°C above the pre-industrial level.</p>
<p>Of this, at least 2°C will emerge by mid-century, and probably a further 3°C a century from now. A temperature increase of this magnitude would be catastrophic for life on Earth. Hansen adds that to avoid such an outcome, brightening Earth is now necessary to halt the warming in the pipeline from past emissions. </p>
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<img alt="Crevices in an ice sheet." src="https://images.theconversation.com/files/564511/original/file-20231208-15-2uidqq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564511/original/file-20231208-15-2uidqq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564511/original/file-20231208-15-2uidqq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564511/original/file-20231208-15-2uidqq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564511/original/file-20231208-15-2uidqq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564511/original/file-20231208-15-2uidqq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564511/original/file-20231208-15-2uidqq.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">
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<span class="caption">Bright surfaces, like ice sheets, reflect light to space.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/deep-crevices-on-ice-sheet-greenland-1641825838">Tobetv/Shutterstock</a></span>
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<p>But at the same time, we must also largely eliminate emissions if we are to stop recreating this problem in the future.</p>
<h2>Still getting hotter…</h2>
<p>We are scientists who study the feasibility and effectiveness of alternative responses to climate change, addressing both the engineering and political realities of enabling change at the scale and speed necessary. </p>
<p>We find Mann’s rebuttal of Hansen’s claims unconvincing. Crucially, Mann does not engage directly with Hansen’s analysis of new data covering the last 65 million years.</p>
<p>Hansen explains how the models used by IPCC scientists to assess future climate scenarios have significantly underestimated the warming effect of increased greenhouse gas emissions, the cooling effect of aerosols and how long the climate takes to respond to these changes. </p>
<p>Besides greenhouse gases, humanity also emits aerosols. These are tiny particles comprising a wide range of chemicals. Some, such as the sulphur dioxide emitted when coal and oil are burned, offset the warming from greenhouse gases by reflecting sunlight back to space. </p>
<p>Others, such as soot, have the opposite effect and add to warming. The cooling aerosols dominate by a large margin.</p>
<p>Hansen projects that in coming months, <a href="https://theconversation.com/air-pollution-cools-climate-more-than-expected-this-makes-cutting-carbon-emissions-more-urgent-192433">lower levels of aerosol pollution</a> from shipping will cause warming of as much as 0.5°C more than IPCC models have predicted. This will take global warming close to 2°C as early as next year, although it is likely then to fall slightly as the present El Niño wanes.</p>
<p>Underpinning Hansen’s argument is his conviction that the climate is more sensitive to greenhouse gases than previously reported. The IPCC estimates that doubling atmospheric CO₂ raises Earth’s temperature by 3°C. Hansen calculates it to be 4.8°C. </p>
<p>This, and the much longer climate response time that Hansen calculates from the historical record, would have a significant impact on climate model projections.</p>
<h2>Time for reflection</h2>
<p>The differences between Mann and Hansen are significant for the global response to climate change. </p>
<p>Mann says that allowing emissions to reach net zero by mid-century is sufficient, while Hansen maintains that on its own it would be disastrous and that steps must now be taken in addition to brighten the planet.</p>
<p>Brightening Earth could also reverse the reductions in reflectivity already caused by climate change. <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021GL094888">Data indicates</a> that from 1998 to 2017, Earth dimmed by about 0.5 watts per square metre, largely due to the loss of ice.</p>
<p>Given what’s at stake, we hope Mann and Hansen resolve these differences quickly to help the public and policymakers understand what it will take to minimise the likelihood of imminent massive and widespread ecosystem destruction and its disastrous effects on humanity. </p>
<p>While 1.5°C may be dead, there may still be time to prevent cascading system failures. But not if we continue to squabble over the nature and extent of the risks.</p>
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<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Is reaching net zero emissions by 2050 enough to halt warming? One leading scientist says no.Robert Chris, Honorary Associate, Geography, The Open UniversityHugh Hunt, Professor of Engineering Dynamics and Vibration, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1982862023-02-13T13:26:11Z2023-02-13T13:26:11ZBig Oil’s trade group allies outspent clean energy groups by a whopping 27x, with billions in ads and lobbying to keep fossil fuels flowing<p><em><a href="https://theconversation.com/los-grupos-aliados-de-las-grandes-petroleras-gastaron-miles-de-millones-en-publicidad-y-grupos-de-presion-para-mantener-el-negocio-de-los-combustibles-fosiles-199848">Leer en español</a>.</em></p>
<p>You’ve probably seen ads promoting gas and oil companies <a href="https://www.axios.com/newsletters/axios-generate-b5679c38-e2cf-40b1-9b9b-cf3e5476a693.html">as the solutions to climate change</a>. They’re meant to be <a href="https://www.ispot.tv/ad/ovGn/exxon-mobil-algae-potential">inspiring and hopeful</a>, with scenes of a green, clean future.</p>
<p>But <a href="https://www.youtube.com/watch?v=bKfLYRtCGY4">shiny ads</a> are not all these companies do to protect their commercial interests in the face of a rapidly heating world. Most <a href="https://link.springer.com/article/10.1007/s10584-022-03466-0">also provide financial support</a> to industry groups that are spending hundreds of millions of dollars on political activities, often to thwart polices designed to slow climate change.</p>
<p>For example, The New York Times recently reported on the Propane Education and Research Council’s <a href="https://www.nytimes.com/2023/01/11/climate/climate-propane-influence-campaign.html">attempts to derail efforts</a> to electrify homes and buildings in New York, in part by committing nearly US$900,000 to the New York Propane Gas Association, which flooded social media with misleading information about energy-efficient heat pumps.</p>
<p>The American Fuel and Petrochemical Manufacturers, which represents oil refiners and petrochemical firms, has <a href="https://www.buzzfeednews.com/article/zahrahirji/edelman-fossil-fuel-pr-climate">spent millions</a> on public relations campaigns, such as promoting a rollback of federal fuel efficiency standards.</p>
<p>These practices have been going on for decades, and evidence shows that industry groups have <a href="https://doi.org/10.1088/1748-9326/ac8ab3">played key roles</a> in <a href="https://www.taylorfrancis.com/books/mono/10.4324/9780429402074/business-battles-us-energy-sector-christian-downie">blocking state and federal climate policies</a>. This matters not just because of the enormous sums the groups are spending, but also because they often act as a <a href="https://www.routledge.com/Business-Battles-in-the-US-Energy-Sector-Lessons-for-a-Clean-Energy-Transition/Downie/p/book/9781138392717">command center</a> for political campaigns to kill pro-climate policies.</p>
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<p>We study the political activities of industry groups. In a recent <a href="https://doi.org/10.1007/s10584-022-03466-0">research paper</a>, we dug through U.S. tax filings to follow the money trail of trade associations engaged on climate change issues and track the billions they have spent to shape federal policy.</p>
<h2>What we found</h2>
<p>After NASA scientist James Hansen <a href="https://www.scribd.com/doc/260149292/Transcript-of-pivotal-climate-change-hearing-1988">sounded the alarm on climate change</a> in 1988, three trade associations – the National Association of Manufacturers, the Edison Electric Institute and the American Petroleum Institute – banded together with a couple of electrical utilities to form the <a href="https://doi.org/10.1080/09644016.2022.2058815">Global Climate Coalition</a>, or GCC.</p>
<p>The GCC systematically opposed any international regulation of climate-warming emissions, and successfully prevented the U.S. from ratifying the <a href="https://unfccc.int/kyoto_protocol">Kyoto Protocol</a>, a 1997 international agreement to reduce greenhouse gas emissions.</p>
<p>This was the first example of trade associations working together <a href="https://www.theguardian.com/environment/2021/nov/18/the-forgotten-oil-ads-that-told-us-climate-change-was-nothing">to stall government action</a> on climate change. Similar efforts continue today.</p>
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<p>So, how much do trade associations spend on political activities, such as public relations? As not-for-profit organizations under the Internal Revenue Code, trade associations have to report their revenue and spending.</p>
<p>We found that trade associations historically opposed to climate policies <a href="https://doi.org/10.1007/s10584-022-03466-0">spent $2 billion</a> in the decade from 2008 to 2018 on political activities, such as advertising, lobbying and political contributions. Together, they outspent climate-supporting industry groups 27 to 1. </p>
<p>The oil and gas sector was <a href="https://doi.org/10.1007/s10584-022-03466-0">the largest</a>, spending $1.3 billion. Across the 89 trade associations we examined in nine different sectors of the U.S. economy between 2008 and 2018, no other group of trade associations came close.</p>
<p><iframe id="PcNSM" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/PcNSM/8/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<h2>No. 1 expense: Advertising and promotion</h2>
<p>What came as more of a surprise as we were tallying up the data was how much trade associations are spending on advertising and promotion. This can include everything from mainstream media ads promoting the industry to hiring public relations firms to target particular issues before Congress.</p>
<p>For example, until they parted ways last year, Edelman, the world’s largest public relations firm, <a href="https://heated.world/p/edelmans-climate-cop-out">received close to $30 million</a> from American Fuel and Petrochemical Manufacturers to promote fossil fuels, reporters at the online news site Heated found.</p>
<p>Our study found that trade associations engaged on climate change issues spent a total of $2.2 billion on advertising and promotion between 2008 and 2018, compared with $729 million on lobbying. As <a href="https://www.opensecrets.org/orgs/american-petroleum-institute/summary?id=D000031493">2022 lobbying data shows</a>, their <a href="https://www.opensecrets.org/orgs/american-fuel-petrochem-manufacturers/summary?id=D000027874">spending continues</a>. While not all of this spending is directly targeting climate policy, climate change is one of the <a href="https://influencemap.org/landing/-a794566767a94a5d71052b63a05e825f-20189">top political issues</a> for many industries in the energy sector.</p>
<p>Media buys are expensive, but these numbers also reflect the specific role trade associations play in protecting the reputation of the firms they represent.</p>
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<figcaption><span class="caption">Trade groups run promotional ads for their industries, as well as negative ads.</span></figcaption>
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<p>One reason that groups like the American Petroleum Institute have historically taken the lead running negative public relations campaigns is so that their members, such as BP and Shell, are not tarred with the same brush, as <a href="https://doi.org/10.1007/s10584-022-03466-0">our interviews with industry insiders confirmed</a>. </p>
<p>However, many firms are now coming under pressure to leave trade associations that oppose climate policies. In one example, the oil giant Total <a href="https://www.washingtonpost.com/climate-environment/2021/01/15/french-oil-giant-total-quits-american-petroleum-institute/">quit API in 2021</a>, citing disagreements over climate positions.</p>
<p>Spending on social media in the weeks ahead of the U.S. midterm elections and during the U.N. Climate Conference in November 2022 offers another window into these groups’ operations.</p>
<p><a href="https://caad.info/wp-content/uploads/2023/01/DDD_ExposingClimateDisinfo-COP27.pdf">A review</a> by the advocacy group Climate Action Against Disinformation found that 87 fossil-fuel-linked groups spent roughly $3 million to $4 million on more than 3,700 ads through Facebook’s parent company alone in the 12 weeks before and during the conference. </p>
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<figcaption><span class="caption">Facebook received millions of dollars to run ads promoting natural gas.</span></figcaption>
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<p>The largest share came from a public relations group representing the American Petroleum Institute and focused heavily on advocating for natural gas and oil and discussing energy security. America’s Plastic Makers spent about $1.1 million on climate-related advertising during the two weeks of the U.N. conference.</p>
<h2>Funneling money to think tanks and local groups</h2>
<p>Trade associations also spent $394 million on grants to other organizations during the decade we reviewed. For example, they gave money to think tanks, <a href="https://www.nytimes.com/2022/10/31/climate/frank-mitloehner-uc-davis.html">universities</a>, charitable foundations and political organizations like associations of mayors and governors.</p>
<p>While some of these grants may be philanthropic in nature, among the trade associations we spoke to, most have a political purpose in mind. Grants channeled to local community groups, as one example, can help boost an industry’s reputation among key constituent groups, and as a result their social license to operate.</p>
<h2>What this means for climate policy</h2>
<p>Fossil fuel companies, which reported <a href="https://www.vox.com/energy-and-environment/2023/2/8/23587955/exxon-chevron-bp-oil-profits-climate">record profits</a> in 2022, still <a href="https://academic.oup.com/book/9937?login=true">spend more</a> on political activities than their trade associations do.</p>
<p>But industry groups historically opposed to climate policies are also big spenders, as our research shows. They outspent those that support actions to slow climate change, such as the solar and wind industries, by a whopping $2 billion to $74.5 million over the 10 years we reviewed.</p>
<p>This likely <a href="https://static1.squarespace.com/static/60bed54ea75154265d5f3862/t/60bee2b67579be685d2e4715/1623122616896/Downie-2018-Business-and-Politics.pdf">helps to explain</a> why it took Congress almost 35 years after Hansen first warned representatives about the dangers of climate change to pass a major climate bill, the 2022 <a href="https://www.congress.gov/bill/117th-congress/house-bill/5376">Inflation Reduction Act</a>.</p><img src="https://counter.theconversation.com/content/198286/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Researchers looked at a decade of political spending by the oil and gas industry and others engaged in climate policy. If money talks, one side had a giant megaphone.Christian Downie, Associate Professor, Australian National UniversityRobert Brulle, Professor of Sociology, Brown UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/928562018-03-25T09:17:47Z2018-03-25T09:17:47ZA Marxist approach appropriate for the climate crisis and the 21st Century<figure><img src="https://images.theconversation.com/files/211176/original/file-20180320-31596-157hdz0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Despite the climate crisis, humans have continued emitting and intensively using fossil fuels.</span> <span class="attribution"><span class="source">EPA</span></span></figcaption></figure><p>Climate change is the most serious challenge the human species faces. Despite numerous warnings – scientific studies, UN declarations, books, movies, progressive media reporting – global leadership has failed humanity. </p>
<p>But how do humans survive the climate crisis? </p>
<p>The climate crisis should be treated as an emergency, demanding transformative politics that gets to the root causes through democratic systemic reforms. These would include remaking how people produce, consume, finance and organise social life.</p>
<p>A civilisation constantly undermining the conditions that sustain life has to be transformed urgently.</p>
<p>Despite the science and global consensus on the climate crisis, humans have continued emitting and intensively using fossil fuels. As a result the world is recording the <a href="https://www.washingtonpost.com/news/energy-environment/wp/2018/01/18/2017-was-among-the-planets-hottest-years-on-record-government-scientists-report/?utm_term=.6662195245e1">hottest years</a> on the planet. A heated planet, as a result of human action, unhinges all certainties and places everything in jeopardy. It challenges fixation with growth economics, “catch up” development and every conception of modern progress. </p>
<p>Most fundamentally, it prompts the question, has globalised capitalism lost its progressiveness? Is today’s fossil fuel driven, hi-tech, scientific, financialised and post-Fordist industrial world leading humanity down a path of destruction? </p>
<p>A new book I’ve <a href="http://witspress.co.za/catalogue/the-climate-crisis/">edited</a>, <em>The Climate Crisis- South African and Global Democratic Eco-Socialist Alternatives</em>, draws from the analysis, concepts and systemic alternatives emerging at the frontiers of climate justice politics. This includes alternatives championed by global social movements such as <a href="https://viacampesina.org/en/">La Via Campesina</a>, the largest peasant movement in the world, progressive Southern intellectuals and movements within Bolivia, Ecuador and Africa. </p>
<h2>Challenging Marxism to meet the challenge</h2>
<p>As in previous volumes in the <a href="http://copac.org.za/democratic-marxism-book-series/">Democratic Marxism series</a>, this one brings together contributions that are thinking with – and learning from – grassroots movements. Many of the contributors are engaged activist scholars, grassroots activists and movement leaders.</p>
<p>This volume also places Marxism in dialogue with contemporary anti-capitalism in a way that draws on its ideological and movement potentials. Marxism in the 20th century as a ruling ideology, mostly as Marxism-Leninism, has pursued policies that have been ruinous to the environment. These have included championing growth at all costs, monopoly one party state control and catch-up industrialisation with capitalist countries. </p>
<p>In this volume nature is placed at the centre of how Marxism understands capitalism, history and alternatives. It confronts the intersections of climate change, patriarchy and racism inherent to capitalism. Marxism is challenged to think and act democratically in the 21st century. It’s tested as an intellectual resource to serve as the basis for a new future.</p>
<p>This is different from socialisms in the 20th century. These where authoritarian (controlled by elites), anti-nature and undermined the power of workers, peasants and progressive social forces. This volume affirms the renewal of socialism in the 21st century in dialogue with Marxism, ecological thought and democratic alternatives emerging from below. </p>
<h2>A heating planet</h2>
<p>In 1988, NASA scientist James Hansen <a href="https://skepticalscience.com/Hansen-1988-prediction-advanced.htm">drew attention</a> to the heating of the earth’s temperature, otherwise known as climate change. Yet over the past two decades the US refused to adopt the <a href="http://unfccc.int/kyoto_protocol/items/2830.php">Kyoto Protocol</a>. This didn’t go far enough but nevertheless locked in common but differentiated responsibilities for industrial countries to cut emissions. Instead, Washington has worked systematically to scuttle the Kyoto Protocol. </p>
<p>In 2006, Hansen <a href="http://www.pnas.org/content/103/39/14288">cautioned</a> that the world has a decade to change the trajectory of greenhouse gas emissions or face irreversible changes which would bring disastrous consequences. </p>
<p>Since this plea was made, another decade has been lost including through the ineffectual <a href="http://unfccc.int/paris_agreement/items/9485.php">“Paris Climate Agreement”</a> <a href="https://www.bostonglobe.com/news/world/2017/06/01/read-obama-statement-paris-climate-agreement/8jA3iHkFL2E1D55c74BnHJ/story.html">championed</a> by the US President Barack Obama but <a href="http://time.com/4802148/paris-agreement-barack-obama-donald-trump/">undermined</a> by incumbent Donald Trump. Today geologists and climate scientists are talking about a dangerous new world: the <a href="https://www.smithsonianmag.com/science-nature/what-is-the-anthropocene-and-are-we-in-it-164801414/">Anthropocene</a>. It’s a world in which humans have changed planetary conditions including climate, breaking a 11 700 year pattern of relatively stable climate known as the <a href="http://www.bbc.co.uk/nature/history_of_the_earth/Holocene">Holocene</a>.</p>
<h2>The realities of climate driven world</h2>
<p>For many the climate crisis is a complex scientific problem. At one level it is. And is very different from daily or seasonal variability in weather. The science of climate change has <a href="https://climate.nasa.gov/evidence/">confirmed</a>, with the measurement of greenhouse gases that human induced climate change is happening. </p>
<p>In 2015, the halfway mark towards catastrophic climate change was broken. This was confirmed by the <a href="https://www.wmo.int/pages/index_en.html">World Meteorological Organisation</a> which broadcast to the world that planetary temperatures have reached a 1 degree Celsius <a href="https://e360.yale.edu/digest/2016_hottest_year_on_record_wmo_12_degrees_c">increase</a> higher than the period prior to the industrial revolution.</p>
<p>The world is moving rapidly closer to a <a href="https://edition.cnn.com/2017/07/31/health/climate-change-two-degrees-studies/index.html">2°C increase</a> in planetary temperature. With this shift, extreme weather events such as droughts, heatwaves, drier conditions enabling fires and floods are becoming more commonplace. Sea levels are also rising, placing many low-lying communities, populous coastal cities and island states in jeopardy. </p>
<p>Climate change on this scale is not expected to unfold in a linear way. Instead, it potentially can happen abruptly or through feedback loops further accelerating runaway climate change. Examples of this include methane release from the Arctic ice sheet, carbon saturation in the oceans and the destruction of rain forests which all feed into the climate change crisis. As the world fails to address the climate crisis, it becomes more complex and more costly.</p>
<p>In response, the <em>Climate Crisis</em> highlights the importance of advancing a deep and just transition that decarbonises society and provides a new basis for organising society to endure climate shocks. </p>
<p>New systems have to be developed through democratic systemic reforms. These would include the rights of nature, degrowth, climate jobs, socially owned renewable energy, a substantive basic income grant, integrated public transport, food sovereignty, solidarity economy and commons approaches to land, water and the cyber sphere.</p><img src="https://counter.theconversation.com/content/92856/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Vishwas Satgar receives funding from the National Institute of Humanities and Social Science and the Rosa Luxemburg Foundation. He is an activist in the South African Food Sovereignty Campaign, he chairs the board of the Cooperative and Policy Alternative Centre (COPAC) and is the editor of the Democratic Marxism book series.</span></em></p>The climate crisis is a complex scientific problem. New systems have to be developed through democratic systemic reforms.Vishwas Satgar, Associate Professor, Department of International Relations, University of the WitwatersrandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/811342017-07-18T15:14:25Z2017-07-18T15:14:25ZInaction on climate change risks leaving future generations $530 trillion in debt<figure><img src="https://images.theconversation.com/files/178553/original/file-20170718-21748-1w9f5te.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">24Novembers / shutterstock</span></span></figcaption></figure><p>By continuing to delay significant reductions in greenhouse gas emissions, we risk handing young people alive today a bill of up to US$535 trillion. This would be the cost of the “negative emissions” technologies required to remove CO₂ from the air in order to avoid dangerous climate change. </p>
<p>These are the main findings of new research published in <a href="http://dx.doi.org/10.5194/esd-8-577-2017">Earth System Dynamics</a>, conducted by an international team led by US climate scientist James Hansen, previously the director of NASA’s Goddard Institute for Space Studies.</p>
<p>The <a href="https://theconversation.com/uk/topics/paris-agreement-23382">Paris Agreement</a> in 2015 saw the international community agree to limit warming to within 2°C. The Hansen team argue that the much safer approach is to reduce atmospheric concentrations of CO₂ from the current annual average of more than 400ppm (parts per million) back to 1980s levels of 350ppm. This is a moderately more ambitious goal than the aspiration announced in Paris to further attempt to limit warming to no more than 1.5°C. Many climate scientists and policymakers believe that either the 2°C or 1.5°C limits will <a href="https://theconversation.com/paris-emissions-cuts-arent-enough-well-have-to-put-carbon-back-in-the-ground-52175">only be possible with negative emissions</a> because the international community will be unable to make the required reductions in time. </p>
<h2>Putting carbon back in the ground</h2>
<p>The most promising negative emissions technology is BECCS – <a href="https://www.carbonbrief.org/beccs-the-story-of-climate-changes-saviour-technology">bioenergy with carbon capture and sequestration</a>. It involves growing crops which are then burnt in power stations to generate electricity. The carbon dioxide produced is captured from the power station chimneys, compressed, and piped deep down into the Earth’s crust where it will be stored for many thousands of years. This scheme would allow us to both generate electricity and reduce the amount of CO₂ in the Earth’s atmosphere.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/178662/original/file-20170718-12568-sbmvws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/178662/original/file-20170718-12568-sbmvws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178662/original/file-20170718-12568-sbmvws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178662/original/file-20170718-12568-sbmvws.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178662/original/file-20170718-12568-sbmvws.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178662/original/file-20170718-12568-sbmvws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178662/original/file-20170718-12568-sbmvws.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178662/original/file-20170718-12568-sbmvws.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Other energy sources are at best carbon-neutral, but BECCS removes more than it emits.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Carbon_flow.jpg">Elrapto</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>BECCS has <a href="http://www.nature.com/nclimate/journal/v4/n10/full/nclimate2392.html">important limits</a>, such as the sheer amount of land, water and fertiliser required to satisfy our energy demand. Perhaps more importantly, it doesn’t exist at anything like the scale required of it. Thus far only small <a href="https://www.washingtonpost.com/news/energy-environment/wp/2017/04/10/the-quest-to-capture-and-store-carbon-and-slow-climate-change-just-reached-a-new-milestone/?utm_term=.417c3c3d83d1">pilot projects</a> have demonstrated its feasibility. <a href="https://www.carbonbrief.org/explainer-10-ways-negative-emissions-could-slow-climate-change">Other negative emissions approaches</a> involve <a href="https://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch11s11-2-2.html">fertilising the ocean</a> to increase photosynthesis, or <a href="http://www.sciencemag.org/news/2017/06/switzerland-giant-new-machine-sucking-carbon-directly-air">direct air capture</a> which sucks CO₂ out of the air and converts it into plastics or other products. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/178664/original/file-20170718-10334-caaytf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/178664/original/file-20170718-10334-caaytf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178664/original/file-20170718-10334-caaytf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178664/original/file-20170718-10334-caaytf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178664/original/file-20170718-10334-caaytf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178664/original/file-20170718-10334-caaytf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178664/original/file-20170718-10334-caaytf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178664/original/file-20170718-10334-caaytf.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"></a>
<figcaption>
<span class="caption">An ethanol production plant in South Dakota, US. We’ll need many more of these – equipped with carbon capture tech – to have an impact on global emissions.</span>
<span class="attribution"><span class="source">Jim Parkin / shutterstock</span></span>
</figcaption>
</figure>
<p>The Hansen team estimate how much it will cost to extract excess CO₂ with BECCS. They conclude that it would be possible to move back to 350ppm mainly with reforestation and improving soils, leaving around 50 billion tonnes of CO₂ to be mopped up with negative emissions technologies (the plants grown for BECCS take in the CO₂, which is then sequestered when burned). </p>
<p>But that’s only if we make significant reductions in rates of emissions right now. If we delay, then future generations would need to extract over ten times more CO₂ beyond the end of this century.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/178558/original/file-20170718-21756-rtjq9r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178558/original/file-20170718-21756-rtjq9r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=205&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178558/original/file-20170718-21756-rtjq9r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=205&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178558/original/file-20170718-21756-rtjq9r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=205&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178558/original/file-20170718-21756-rtjq9r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=258&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178558/original/file-20170718-21756-rtjq9r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=258&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178558/original/file-20170718-21756-rtjq9r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=258&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Scenarios for future carbon dioxide emissions and extraction.</span>
</figcaption>
</figure>
<p>They estimate costs between US$150-350 for each tonne of carbon removed via negative emissions technologies. If global emissions are reduced by 6% each year – a very challenging but not impossible scenario – then bringing CO₂ concentrations back to 350ppm would cost US$8-18.5 trillion, spread over 80 years at US$100-230 billion a year. </p>
<p>If emissions remain flat or increase at 2% a year, then total cost balloons to at least US$89 trillion and potentially as much as US$535 trillion. That’s US$1.1 to US$6.7 trillion every year for eight decades. </p>
<p>To give these numbers some context, the <a href="https://www.cbo.gov/topics/budget">entire US federal budget</a> is about US$4 trillion, while annual spending by all countries on <a href="http://www.newsweek.com/global-defence-spending-western-budgets-shrink-444319">military and defence</a> is US$1.7 trillion.</p>
<h2>A climate balancing act</h2>
<p>Humans have pumped over <a href="https://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf">1.5 trillion tonnes</a> of CO₂ into the atmosphere since 1750. It is not just the amount, but the rate at which this CO₂ has been added. The oceans can absorb extra CO₂ but not fast enough to remove all human inputs and so it has been <a href="https://www.esrl.noaa.gov/gmd/ccgg/trends/history.html">progressively building up in the atmosphere</a>. This extra CO₂ traps more heat than would otherwise escape out into space. More energy is therefore entering the climate system than leaving it. </p>
<p>Over decades and centuries the climate will move back into balance with the same amount of energy leaving as entering. But this will be at a higher temperature with among other things less ice, higher sea levels, more heatwaves, and more floods. The last time the Earth’s climate experienced such an energy imbalance was the <a href="https://theconversation.com/the-last-time-earth-was-this-hot-hippos-lived-in-britain-thats-130-000-years-ago-53398">Eemian interglacial period</a> some 115,000 years ago. At that time global sea levels were six to nine metres higher than today. </p>
<p>The Hansen team argues that even maintaining the current energy imbalance risks locking in several metres of sea level rise. That is because slow processes such as melting ice sheets still haven’t “caught up”. The longer the climate is held out of balance, the greater their effect will be.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/178676/original/file-20170718-10283-1ed7x1m.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/178676/original/file-20170718-10283-1ed7x1m.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178676/original/file-20170718-10283-1ed7x1m.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=343&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178676/original/file-20170718-10283-1ed7x1m.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=343&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178676/original/file-20170718-10283-1ed7x1m.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=343&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178676/original/file-20170718-10283-1ed7x1m.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=431&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178676/original/file-20170718-10283-1ed7x1m.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=431&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178676/original/file-20170718-10283-1ed7x1m.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=431&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Climate change isn’t instant. Even if carbon emissions ceased today, ice caps would keep melting for decades.</span>
<span class="attribution"><span class="source">Bernhard Staehli / shutterstock</span></span>
</figcaption>
</figure>
<p>One argument against making drastic cuts to greenhouse gas emissions is that it will harm economies as our industries are still largely fossil fuelled. Responding to climate change needs to balance the desire to continue to grow economies today with avoiding disastrous climate change or prohibitively expensive remedies tomorrow. </p>
<p>Whatever assumptions you make about economic growth, or however much you discount future costs, it’s unimaginable that US$535 trillion could be afforded. While these costs will be spread over 80 years, this will also be a period in which the global population will increase from seven billion to perhaps <a href="https://theconversation.com/can-the-earth-feed-11-billion-people-four-reasons-to-fear-a-malthusian-future-43347">11 billion and beyond</a>. Humanity will need to grow enough crops to feed these billions while fuelling BECCS schemes at a time when climate change will already be impacting food production. There are also no guarantees that BECCS or any other negative emission technologies will actually work. If they fail then large amounts of CO₂ could be released very rapidly with disastrous consequences.</p>
<p>By delaying significant carbon emission reductions we risk handing both an impossible financial and technological burden to future generations. Our children and grandchildren may be unable to understand how we negotiated such an arrangement on their behalf.</p><img src="https://counter.theconversation.com/content/81134/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Dyke is as an editor of the EGU journal Earth System Dynamics. He served as the handling editor for the Hansen et al manuscript discussed in this article</span></em></p>New research calculates the huge cost of ‘negative emissions’ technologies that will be required to avoid dangerous climate change.James Dyke, Lecturer in Sustainability Science, University of SouthamptonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/568072016-03-30T19:10:06Z2016-03-30T19:10:06ZWhat does the science really say about sea-level rise?<figure><img src="https://images.theconversation.com/files/116725/original/image-20160330-28472-ebelg2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Glaciers have been a major contributor to sea-level rise.</span> <span class="attribution"><span class="source">Knut Christianson</span></span></figcaption></figure><p>A recent <a href="http://www.atmos-chem-phys.net/16/3761/2016/acp-16-3761-2016.html">high-profile study</a> led by US climatologist James Hansen has warned that sea levels could rise by several metres by the end of this century. How realistic is this scenario? </p>
<p>We can certainly say that sea levels are rising at an accelerating rate, after several millennia of relative stability. The question is how far and how fast they will go, compared with Earth’s previous history of major sea-level changes.</p>
<p>Seas have already <a href="http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s10712-011-9119-1">risen by more than 20 cm</a> since 1880, affecting coastal environments around the world. Since 1993, sea level has been rising faster still (see chapter 3 <a href="http://www.ipcc.ch/report/ar5/wg1/">here</a>), at about 3 mm per year (30 cm per century). </p>
<p>One key to understanding future sea levels is to look to the past. The <a href="http://science.sciencemag.org/content/349/6244/aaa4019">prehistoric record</a> clearly shows that sea level was higher in past warmer climates. The best evidence comes from the most recent interglacial period (129,000 to 116,000 years ago), when sea level was 5-10 m higher than today, and high-latitude temperatures were at least 2°C warmer than at present. </p>
<p>The two largest contributions to the observed rise since 1900 are thermal expansion of the oceans, and the loss of ice from glaciers. Water stored on land (in lakes, reservoirs and aquifers) has also made a small contribution. Satellite observations and models suggest that the amount of sea-level rise due to the Greenland and Antarctic ice sheets has increased since the early 1990s. </p>
<p>Before then, their contributions are not well known but they are unlikely to have contributed more than 20% of the observed rise. </p>
<p>Together, these contributions provide a reasonable explanation of the observed 20th-century sea-level rise.</p>
<h2>Future rise</h2>
<p>The Intergovernmental Panel on Climate Change (IPCC) projections (see chapter 13 <a href="http://www.ipcc.ch/report/ar5/wg1/">here</a>) forecast a sea-level rise of 52-98 cm by 2100 if greenhouse emissions continue to grow, or of 28-61 cm if emissions are strongly curbed. </p>
<p>The majority of this rise is likely to come from three sources: increased ocean expansion; glacier melt; and surface melting from the Greenland ice sheet. These factors will probably be offset to an extent by a small increase in snowfall over Antarctica. </p>
<p>With continued emissions growth, it is entirely possible that the overall rate of sea-level rise could reach 1 m per century by 2100 – a rate not seen since the last global ice-sheet melting event, roughly 10,000 years ago.</p>
<p>Beyond 2100, seas will continue to rise for many centuries, perhaps even millennia. With continued growth in emissions, the IPCC has projected a rise of as much as 7 m by 2500, but also warned that the available ice-sheet models may underestimate Antarctica’s future contribution. </p>
<p>The joker in the pack is what could happen to the flow of ice from the Antarctic ice sheet directly into the ocean. The IPCC estimated that this could contribute about 20 cm of sea-level rise this century. But it also recognised the possibility of an additional rise of several tens of centimetres this century if the ice sheet became rapidly destabilised. </p>
<p>This could happen in West Antarctica and in parts of the East Antarctic ice sheets that are resting on ground below sea level, which gets deeper going inland from the coast. If relatively warm ocean water penetrates beneath the ice sheet and melts its base, this would cause the grounding line to move inland and ice to flow more rapidly into the ocean.</p>
<p>Several recently published studies have confirmed that parts of the West Antarctic ice sheet are already in <a href="https://theconversation.com/we-can-now-only-watch-as-west-antarcticas-ice-sheets-collapse-26957">potentially unstoppable retreat</a>. But for these studies the additional rise above the IPCC projections of up to 98 cm by 2100 from marine ice sheet instability was more likely to be just one or two tenths of a metre by 2100, rather than several tenths of a metre allowed for in the IPCC report. This lower rise was a result of more rigorous ice-sheet modelling, compared with the results available at the time of the IPCC’s assessment.</p>
<h2>How stable are ice sheets?</h2>
<p>Ocean temperatures were thought to be the major control in triggering increased flow of the Antarctic ice sheet into the ocean. Now a <a href="http://nature.com/articles/doi:10.1038/nature17145">new study published in Nature</a> by US researchers Robert DeConto and David Pollard has modelled what would happen if you factor in increased surface melting of ice shelves due to warming air temperatures, as well as the marine melting. </p>
<p>Such an ice-shelf collapse has already been seen. In 2002, the Larsen-B Ice Shelf on the Antarctic Peninsula <a href="http://earthobservatory.nasa.gov/Features/WorldOfChange/larsenb.php">disintegrated</a> into thousands of icebergs in a matter of weeks, allowing glaciers to flow more rapidly into the ocean. The IPCC’s predictions had considered such collapses unlikely to occur much before 2100, whereas the new study suggests that ice-sheet collapse could begin seriously affecting sea level as early as 2050. </p>
<p>With relatively high greenhouse emissions (a scenario referred to in the research literature as <a href="http://link.springer.com/article/10.1007%2Fs10584-011-0149-y">RCP8.5</a>), the new study forecasts a rise of about 80 cm by 2100, although it also calculated that this eventuality could be almost totally averted with lower emissions. But when the model parameters were adjusted to simulate past climates, the Antarctic contribution was over 1 m by 2100 and as much as 15 m by 2500. </p>
<p>Greenland’s ice sheet is crucially important too. Above a certain threshold, warming air temperatures would cause surface melting to outstrip snow accumulation, leading to the ice sheet’s eventual collapse. That would add an extra 7 m to sea levels over a millennium or more. </p>
<p>The problem is that we don’t know where this threshold is. It could be as little as 1°C above pre-industrial average temperatures or as high as 4°C. But given that present-day temperatures are already almost 1°C above pre-industrial temperatures, it is possible we could cross this threshold this century, regardless of where exactly it is, particularly for high-emission scenarios. </p>
<p>Overall, then, it is clear that the seeds for a multi-metre sea-level rise could well be sown during this century. But in terms of the actual rises we will see in our lifetimes, the available literature suggests it will be much less than the 5 m by 2050 anticipated by Hansen and his colleagues.</p>
<p>The wider question is whether the ice-sheet disintegration modelled by DeConto and Pollard will indeed lead to rises of the order of 15 m over the coming four centuries, as their analysis and another <a href="http://www.nature.com/nclimate/journal/v6/n4/full/nclimate2923.html">recent paper</a> suggest. Answering that question will require more studies, with a wider range of climate and ice-sheet models.</p>
<hr>
<p><em>John will be on hand for an Author Q&A between 2 and 3pm AEDT on Thursday, March 31, 2016. Post your questions in the comments section below.</em></p><img src="https://counter.theconversation.com/content/56807/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Church receives funding from the Australian Climate Change Science Program. </span></em></p><p class="fine-print"><em><span>Peter Clark receives funding from the U.S. National Science Foundation.</span></em></p>Could sea levels really rise by several metres this century. Probably not, although this century’s greenhouse emissions could potentially set the stage for large rises in centuries to come.John Church, CSIRO Fellow, CSIROPeter Clark, Distinguished Professor of Earth, Ocean, and Atmospheric Sciences, Oregon State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/456552015-08-07T06:22:43Z2015-08-07T06:22:43ZHow to make sense of ‘alarming’ sea level forecasts<figure><img src="https://images.theconversation.com/files/91125/original/image-20150807-4388-v1vzpq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Sea level rise is one of the biggest worries of climate change. This image is from the Witness King Tides project, which aims to visualise sea level rise using large tides and storm surges. </span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/witnesskingtides/12278497275/">Witness King Tides/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span></figcaption></figure><p>You may have read recent reports about huge changes in sea level, inspired by <a href="http://www.atmos-chem-phys-discuss.net/15/20059/2015/acpd-15-20059-2015.html">new research</a> from James Hansen, NASA’s former Chief Climate Scientist, at Columbia University. Sea level rise represents one of the most worrying aspects of global warming, potentially displacing millions of people along coasts, low river valleys, deltas and islands. </p>
<p>The Intergovernmental Panel on Climate Change, the UN’s scientific climate body, <a href="https://www.ipcc.ch/pdf/unfccc/cop19/3_gregory13sbsta.pdf">forecasts</a> rises of approximately 40 to 60 cm by 2100. But other studies have found much greater rises are likely.</p>
<p>Hansen and 16 co-authors found that with warming of 2C sea levels could rise by several metres. Hansen’s study was published in the open-access journal Atmospheric Chemistry and Physics Discussion, and has not as yet been peer-reviewed. It received much media coverage for its <a href="http://newsbusters.org/blogs/business/joseph-rossell/2015/07/28/media-hype-hansens-latest-alarming-prediction-sea-levels">“alarmist” findings</a>. </p>
<p>So how should we make sense of these dire forecasts? </p>
<h2>What we’re pretty sure about</h2>
<p>According to the <a href="https://www.ipcc.ch/pdf/unfccc/cop19/3_gregory13sbsta.pdf">IPCC</a> sea level rise has accelerated from 0.05 cm each year during 1700-1900 to 0.32 cm each year during 1993-2010. Over the next century the IPCC expects an average rise of 0.2 to 0.8 cm each year. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/90825/original/image-20150805-12011-1e40392.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/90825/original/image-20150805-12011-1e40392.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/90825/original/image-20150805-12011-1e40392.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/90825/original/image-20150805-12011-1e40392.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/90825/original/image-20150805-12011-1e40392.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/90825/original/image-20150805-12011-1e40392.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/90825/original/image-20150805-12011-1e40392.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/90825/original/image-20150805-12011-1e40392.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Observed and projected sea level rise.</span>
<span class="attribution"><a class="source" href="https://www.ipcc.ch/pdf/unfccc/cop19/3_gregory13sbsta.pdf">IPCC AR5</a></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/90826/original/image-20150805-11984-11cfnkn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/90826/original/image-20150805-11984-11cfnkn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/90826/original/image-20150805-11984-11cfnkn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=361&fit=crop&dpr=1 600w, https://images.theconversation.com/files/90826/original/image-20150805-11984-11cfnkn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=361&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/90826/original/image-20150805-11984-11cfnkn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=361&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/90826/original/image-20150805-11984-11cfnkn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=454&fit=crop&dpr=1 754w, https://images.theconversation.com/files/90826/original/image-20150805-11984-11cfnkn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=454&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/90826/original/image-20150805-11984-11cfnkn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=454&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sea level rise has accelerated.</span>
<span class="attribution"><a class="source" href="https://www.ipcc.ch/pdf/unfccc/cop19/3_gregory13sbsta.pdf">IPCC AR5</a></span>
</figcaption>
</figure>
<p>The collapse of the West Antarctic ice sheet would add several tens of centimetres to the total. </p>
<p>The IPCC report adds that “it is very likely that there will be a significant increase in the occurrence of future sea level extremes” and “it is virtually certain that global mean sea level rise will continue for many centuries beyond 2100, with the amount of rise dependent on future emissions”.</p>
<h2>Looking to the past</h2>
<p>The IPCC estimates stand in sharp contrast to projections made by some climate scientists, in particular James Hansen who pointed out <a href="http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_1.pdf">in 2007</a> and <a href="http://www.huffingtonpost.com/dr-james-hansen/multi-meter-sea-level-rise-is-an-issue-for-todays-public_b_7875828.html">in his and his colleagues’ latest study</a> of the effects of ocean warming on the ice sheets.</p>
<p>The IPCC reports did not take into account rates of dynamic ice sheet breakdown, despite satellite gravity measurements reported in the <a href="http://onlinelibrary.wiley.com/doi/10.1002/2014GL061052/abstract">peer-reviewed literature</a> by <a href="http://onlinelibrary.wiley.com/doi/10.1002/2014GL061052/abstract">other scientists</a>. </p>
<p><a href="http://onlinelibrary.wiley.com/doi/10.1029/2009GL040222/abstract">In Greenland</a>, ice loss reached around 280 gigatonnes of ice each year during 2003-2013, whereas <a href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.170.8753&rep=rep1&type=pdf">in Antarctica</a> the loss reached around 180 gigatonnes of ice each year during the same period. Both ice sheets appear to be undrgoing accelerated rates of ice melt, as shown in the diagrams.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/90827/original/image-20150805-11977-ra32zm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/90827/original/image-20150805-11977-ra32zm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/90827/original/image-20150805-11977-ra32zm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=456&fit=crop&dpr=1 600w, https://images.theconversation.com/files/90827/original/image-20150805-11977-ra32zm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=456&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/90827/original/image-20150805-11977-ra32zm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=456&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/90827/original/image-20150805-11977-ra32zm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=573&fit=crop&dpr=1 754w, https://images.theconversation.com/files/90827/original/image-20150805-11977-ra32zm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=573&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/90827/original/image-20150805-11977-ra32zm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=573&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Melting of the Greenland ice sheet recorded by satellites.</span>
<span class="attribution"><a class="source" href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.170.8753&amp;rep=rep1&amp;type=pdf">GRACE</a></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/90828/original/image-20150805-12018-17jlz34.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/90828/original/image-20150805-12018-17jlz34.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/90828/original/image-20150805-12018-17jlz34.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=467&fit=crop&dpr=1 600w, https://images.theconversation.com/files/90828/original/image-20150805-12018-17jlz34.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=467&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/90828/original/image-20150805-12018-17jlz34.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=467&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/90828/original/image-20150805-12018-17jlz34.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=586&fit=crop&dpr=1 754w, https://images.theconversation.com/files/90828/original/image-20150805-12018-17jlz34.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=586&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/90828/original/image-20150805-12018-17jlz34.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=586&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Melting of the West Antarctic ice sheet recorded by satellites.</span>
<span class="attribution"><a class="source" href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.170.8753&amp;rep=rep1&amp;type=pdf">GRACE</a></span>
</figcaption>
</figure>
<p>Hansen and his 16 colleagues reach their conclusion by looking at both the present and the past. During the Eemian interglacial, a period between ice ages around 130,000–115,000 years ago, average global temperatures were around <a href="http://www.nature.com/nature/journal/v493/n7433/full/nature11789.html">1C warmer</a> than temperatures before the industrial revolution – that is, similar to today’s temperatures. In Greenland temperatures were about 8C warmer (the rise in polar temperatures is generally higher than the rise in tropical and subtropical temperatures, due to the ice-water albedo contrast effect). This led to sea level rise of around <a href="http://www.realclimate.org/index.php/archives/2013/01/the-greenland-melt/">6-7 metres</a>, to a large extent due to melting of the Antarctic ice sheet.</p>
<p>The study points out that during the Eemian contact between the warming ocean and ice sheets led to abrupt disintegration of the ice, raising sea levels by several metres over period of 50-200 years, an extreme rate exceeding current IPCC estimates. The concern is that similar high rates of warming and of sea level rise may pertain in future.</p>
<p>For these reasons Hansen’s group considers sea level could reach several meters toward the end of the century.</p>
<p>These authors state: “We conclude that 2C global warming above the pre-industrial level, which would spur more ice shelf melt, is highly dangerous. Earth’s energy imbalance, which must be eliminated to stabilize climate, provides a crucial metric.”</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/90829/original/image-20150805-12011-131iaae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/90829/original/image-20150805-12011-131iaae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/90829/original/image-20150805-12011-131iaae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/90829/original/image-20150805-12011-131iaae.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/90829/original/image-20150805-12011-131iaae.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/90829/original/image-20150805-12011-131iaae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/90829/original/image-20150805-12011-131iaae.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/90829/original/image-20150805-12011-131iaae.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Earth with a sea level rise of six meters.</span>
<span class="attribution"><a class="source" href="http://blogs.agu.org/geospace/2014/05/15/humans-caused-nearly-90-percent-sea-level-rise-warming-upper-ocean-study-says/">NASA</a></span>
</figcaption>
</figure>
<h2>Criticisms of the study</h2>
<p><a href="http://www.washingtonpost.com/news/energy-environment/wp/2015/07/23/controversial-sea-level-rise-paper-is-now-published-online/">Extensive criticism</a> of this conclusion followed. Kevin Trenberth, of the US National Centre for Atmospheric Research, stated “there are way too many assumptions and extrapolations for anything here to be taken seriously other than to promote further studies.”</p>
<p>Greg Holland, also from the US National Centre for Atmospheric Research, stated: “There is no doubt that the sea level rise, within the IPCC, is a very conservative number, so the truth lies somewhere between IPCC and [James Hansen].”</p>
<p>Michael Mann <a href="http://www.climatedepot.com/2015/07/24/nasas-ex-con-james-hansen-gets-dissed-by-global-warming-establishment-warmists-say-sea-level-rise-study-based-on-flimsy-evidence-rife-with-speculation/#ixzz3hphhoQGi">stated</a> Hansen’s estimates are prone to a very large “extrapolation error”. </p>
<p>Media comments range from <a href="http://thinkprogress.org/climate/2015/07/27/3684564/james-hansen-climate-danger-hyper-anthropocene/">positive</a> to <a href="http://www.climatedepot.com/2015/07/24/nasas-ex-con-james-hansen-gets-dissed-by-global-warming-establishment-warmists-say-sea-level-rise-study-based-on-flimsy-evidence-rife-with-speculation/">derogatory</a>. However, few comments respond in detail to the comprehensive analysis by the authors of Hansen’s 2015 paper.</p>
<h2>Could it be worse?</h2>
<p>The consequences of advanced ice melt include the <a href="http://iopscience.iop.org/1748-9326/2/2/024002">increased discharge of icebergs</a> from a disintegrating ice sheet, as occurred in the past during stadial phases of interglacial periods. Stadials are sharp cooling phases following peak temperatures, caused by the discharge of cold melt water into the ocean. Such discharges constitute a negative feedback, namely cooling.</p>
<p>Past stadial phases, in the wake of peak temperatures, included the Younger dryas (12,900 – 11,700 years-ago) and melting of the Laurentian ice sheet <a href="http://onlinelibrary.wiley.com/doi/10.1029/2007PA001457/pdf">8,500 years-ago</a>. </p>
<p>A stadial freeze, predicted due to a collapse of the <a href="http://earthsky.org/earth/rapid-collapse-of-atlantic-ocean-circulation-possible-new-study-suggests">North Atlantic Thermohaline Current</a> would follow in the wake of large-scale melting and discharge of large parts of the Greenland ice sheet. With further rise in atmospheric CO2 this would constitute a transient stage in global warming.</p>
<p>Warming of <a href="https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter12_FINAL.pdf">2-4C</a> implies a rise in sea level by several to many metres. Future sea level rise, once it reaches equilibrium with temperature rise of about 2C above pre-industrial temperature, could reach levels on the scale of the Pliocene (pre-2.6 million years ago) around 25+/-12 metres. Temperature rise of 4C higher than pre-industrial would be consistent with peak Miocene (about 16 million years ago) equilibrium sea levels of about 40 meters. </p>
<p>We don’t know how long it would take for seas to rise that high with rising temperatures. However the extreme rise rate of atmospheric greenhouse gas concentrations, <a href="http://www.esrl.noaa.gov/gmd/ccgg/trends/">higher than 2 ppm CO2 per year</a>, if continues, threatens an accelerating rate of sea level rise. </p>
<p>If so, it follows human civilisation has now begun to preside over a major change to the map of planet Earth.</p><img src="https://counter.theconversation.com/content/45655/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Glikson 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>Sea level rise represents one of the most worrying aspects of global warming, potentially displacing millions of people along coasts, low river valleys, deltas and islands.Andrew Glikson, Earth and paleo-climate scientist, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/451392015-07-23T20:09:33Z2015-07-23T20:09:33ZStudy predicts multi-meter sea level rise this century, but not everyone agrees<figure><img src="https://images.theconversation.com/files/89554/original/image-20150723-22849-mymo1f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Study raises new questions over the rate of ice melting, and thus sea level rise. </span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/gsfc/15572202849/in/photolist-pJ4Bo2-8SjsBk-pJ6Nhm-pJ87s6-bVeG6j-aBwCF5-pYoCZU-aBcsF2-axdGwx-bVeFVy-aBf9ds-b6AwCF-79KYY4-aBf95E-7Ftz9v-btRFYj-azfu9R-7byYPM-awDuFt-33fGbC-aACpiZ-7Ftzc2-aAF8Km-bQC4LF-e4X8x2-aBcsCH-awKfDu-dCbfMZ-bmxWBv-bGLuDK-bGLuKe-bGLuHX-aAF8HC-awGadH-5qbnQZ-7jHRYF-7HaWuZ-9h8Eev-9h8EiV-7Ftz7a-ppC5pB-pYGFbS-aACphp-dWcWed-9h8EbF-ay3rhK-nYoh6C-8xvSZ9-8XULfV-qNvb1c">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>There’s a new study that’s getting a fair amount of attention in the climate science community and the popular press.</p>
<p>Published online in <a href="http://www.atmos-chem-phys-discuss.net/15/20059/2015/acpd-15-20059-2015.pdf">Atmospheric Chemistry and Physics</a>, the paper argues that melting from Greenland and Antarctica will <a href="http://www.livescience.com/51619-dire-climate-warning-by-nasa-scientist.html?cmpid=NL_OAP_weekly_2015-07-21">occur faster than previous projections</a>, leading to rapid sea level rise of several meters, potentially this century. It looks at the prehistoric record to conclude that ice sheets are vulnerable to “non-linear” disintegration, or rapid melting from higher temperatures. It builds on a study published last year that found <a href="https://theconversation.com/we-can-now-only-watch-as-west-antarcticas-ice-sheets-collapse-26957">that melting in West Antarctica</a> was effectively unstoppable.</p>
<p>The lead author of the study is <a href="http://www.columbia.edu/%7Ejeh1/">Dr James Hansen</a>, the former director of the NASA Goddard Institute for Space Studies and now adjunct professor at Columbia University’s Earth Institute, who has become a high-profile activist for policies to reduce greenhouse gas emissions. Among its most alarming conclusions are: </p>
<blockquote>
<p>Our analysis paints a different picture than [the United Nations] IPCC (2013) for how this…phase is likely to proceed if GHG (greenhouse gas) emissions grow at a rate that continues to pump energy at a high rate into the ocean. We conclude that multi-meter sea level rise would become practically unavoidable. Social disruption and economic consequences of such large sea level rise could be devastating. It is not difficult to imagine that conflicts arising from forced migrations and economic collapse might make the planet ungovernable, threatening the fabric of civilization.</p>
</blockquote>
<p>As a climate scientist, I find that the study from Hansen et al is provocative and intriguing. But it is rife with speculation and “what if” scenarios. It has many conjectures and huge extrapolations based on what I see as quite flimsy evidence, but evidence nonetheless. In that regard, it raises good questions and topics worthy of further exploration, but it is not a document that can be used for setting policy for addressing climate change, although that appears to be its intent.</p>
<h2>Models and paleo-data</h2>
<p>The paper is long. It hinges upon interpretation of paleo, or prehistoric, and other data that is apt to be somewhat controversial because of dating uncertainties and conversion of proxy data to geophysical quantities. </p>
<p>It uses a model that does not, in my view, have a very good climate simulation. There are no differences between model results and observations shown, and some errors appear to be large. No mention is made of short-term phenomena, including the El Niño Southern Oscillation (ENSO) or Pacific decadal variations that dominate interannual and decadal variability in the real world, and which are a key to understanding the <a href="http://onlinelibrary.wiley.com/doi/10.1002/2013EF000165/full">recent hiatus</a> in the rate of rising surface temperatures. This absence is significant because recent trends based on short-term fluctuations are not representative of longer-term trends, although frequently interpreted as such.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/74863/original/image-20150315-7058-l65n7s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/74863/original/image-20150315-7058-l65n7s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/74863/original/image-20150315-7058-l65n7s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/74863/original/image-20150315-7058-l65n7s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/74863/original/image-20150315-7058-l65n7s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/74863/original/image-20150315-7058-l65n7s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/74863/original/image-20150315-7058-l65n7s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Any changes to projected rates of sea level rise have deep implications to many coastal areas.</span>
<span class="attribution"><a class="source" href="http://eoimages.gsfc.nasa.gov/images/imagerecords/84000/84737/iss041e074232_lrg.jpg">NASA</a></span>
</figcaption>
</figure>
<p>In their section 4.5, the authors point out the need to simulate a number of features realistically, and the model does not really do them very well, especially basic things like sea surface salinity. So the relevance of the model is not established. Yet, they use the model for a number of highly artificial experiments that are supposed to depict melting of ice at high latitudes. </p>
<p>These experiments introduce a lot of very cold fresh water in various places, and then they see what happens. The question is: how relevant are these to the real world and what is happening as global warming progresses? They do not seem at all realistic to me.</p>
<p>A key to a lot of this is how cloud cover changes as a result of melting and changing ocean temperatures, and one needs to get clouds right in the first place to have confidence in the results. Unfortunately, this is an area where major problems exist. The models have far too much sunshine penetrating to the surface over the southern oceans compared with observations. </p>
<h2>Trying too hard to make a case?</h2>
<p>No doubt all of the changes in the southern ocean, featured strongly by Hansen et al, play an important role, but data there are poor, and changes are not well-known. In particular, the <a href="https://theconversation.com/what-caused-the-pause-in-global-warming-32257">recent hiatus</a> in global warming greatly influences observations, which can therefore be quite misleading with regards to long-term trends. Although Hansen argues that the real world is responding even faster than in the model scenarios, this is not at all clear owing to the natural variability.</p>
<p>The paper is quite well-written and a <em>tour de force</em> in many respects, but there are way too many assumptions and extrapolations for anything here to be taken seriously other than to promote further studies. </p>
<p>The authors often say that “these model limitations must be kept in mind” – and there are many other model limitations not discussed – but then they do not keep them in mind when drawing conclusions. I strongly agree with some of the conclusions with regard to the need for immediate actions to reduce emissions, but it seems that this study has gone out of its way to make the case, stretching credibility.</p><img src="https://counter.theconversation.com/content/45139/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kevin Trenberth does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>NASA’s former climate chief, James Hansen, is lead author on a paper that predicts rapidly rising seas this century, but not all climate scientists believe the study’s models are convincing.Kevin Trenberth, Distinguished Senior Scientist, National Center for Atmospheric Research Licensed as Creative Commons – attribution, no derivatives.