The West Antarctic Ice Sheet in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC): a key threat, a key uncertainty

Transcription

1 Agenda Item: ATCM 14, CEP 7 Presented by: ASOC Original: English Submitted: 31/03/2014 The West Antarctic Ice Sheet in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC): a key threat, a key uncertainty 1

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3 The West Antarctic Ice Sheet in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC): a key threat, a key uncertainty Introduction Information paper submitted by ASOC 1 The Intergovernmental Panel on Climate Change (IPCC) produces assessment reports on the state of climate science every 6-7 years. While there are other important assessment reports with more focused topics (for example, those published by the Royal Academy of Sciences (UK) or the National Research Council (US) or regions (for example, the SCAR ACCE report)), the IPCC provides a well-respected and well-rounded overview of global climate change. The IPCC s assessment reports have continued to track research as it changes and clarifies our understanding of anthropogenic global warming. Each report has provided strong language about the scientific consensus on anthropogenic climate change, with AR5 authors stating that, warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased 2. The IPCC is also clear about anthropogenic contributions to climate change, by noting that human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system. 3 It should be noted here that only the first working group report out of three has been published at the time of writing: this information paper uses material from the assessment report by Working Group I on the Physical Science Basis. Reports by Working Group II on Impacts, Adaptation, and Vulnerability and Working Group III on Mitigation will be published on March 31, and April 14, 2014, respectively, using the scientific material from Working Group I. This information paper will focus on one of the most uncertain and most globally relevant IPCC assessment topics: sea level rise, particularly the contribution of ice sheets, especially the unstable West Antarctic Ice Sheet. We will examine the new projections from the Fifth Assessment Report of the IPCC, discuss the technical and numerical changes from previous projections, and analyse implications for the Antarctic region and ATS. New Sea Level Rise Projections and the Ice Sheets Published in 2007, the sea level rise projections in IPCC s AR4 were controversial because they lacked any contribution for dynamical ice loss; that is, ice sheet collapse. The authors stated that uncertainty was simply too high to make a credible projection 4. Some critics, including fellow IPCC authors, contended that a more serious effort, such as using other methods for projection, could have been made 5. 1 Lead author Dr. Jessica O Reilly, with comments from Lyn Goldsworthy, Pam Pearson, Dr. Ricardo Roura and Dr. Rodolfo Werner. 2 IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Page 4. 3 IPCC 2013, 15 4 Intergovernmental Panel on Climate Change (IPCC). Climate Change 2007: The Physical Science Basis. Edited by Solomon, S, Qin, D, Manning, M, Chen, Z, Marquis, M, Averyt, KB, Tignor, M and Miller, HL Cambridge University Press, Cambridge. 5 Oppenheimer M, O Neill BC, Webster M and Agrawala S (2007) Climate change: The limits of consensus. Science 317(5844):

4 In the recently published AR5, the authors continued to grapple with high uncertainty relating to dynamical changes in the ice sheet. However, they attempted to manage this differently than in AR4 and included a wider breadth of information. Also, there have been strides made in understanding the climate and ice behaviour of the Earth s past, known as paleoclimatic data, as well as in several aspects of climate modelling. The IPCC prefers making projections using process-based models. These models are improving, though they do not adequately include (and in some cases, explicitly exclude) ice sheet collapse into their projections. In all of the scenarios in AR5, assessors provide a range of global sea level rise at 28-98cm over the next century, with means ranging from 44-74cm. It is important to note that these numbers form the LIKELY range (66% confidence interval), not the worst case scenario, which is what local planners use to mitigate risk. Indeed, the sea level rise chapter authors wrote a letter to Science explaining their language as well as asserting that much of their uncertainty and upper bound projections would be based on West Antarctic Ice Sheet dynamics 6. AR5 sea level rise projections are, on average, higher than the previous assessment reports. As our scientific understanding improves, the projections tend to go up. In 2007 s AR4, the sea level rise assessors only relied on models and did not consider alternative methods to projections in much detail. In 2013 s AR5, the assessors included projections from two sources in addition to models: 1) expert elicitation and 2) semi-empirical methods. While these projections did not figure into the main sea level rise projections above, the authors included these low confidence methods in AR5 to provide some insight into estimates involving methods alternative to models. The IPCC authors cited the most recent expert elicitation 7 to underscore the wide spread of projections about if and when the West Antarctic Ice Sheet might collapse and the expert uncertainty surrounding it. The major scientific uncertainty is the potential for the Antarctic ice sheet to disintegrate, causing a relatively rapid and large increase in global sea level. While a major field of inquiry supported by many National Antarctic Programs, the complex processes of ice sheets, particularly those of WAIS, which sits below sea level, make the likelihood of ice sheet collapse difficult to project. Nonetheless, the projected sea level rise that would occur with the collapse of the West Antarctic Ice Sheet makes gauging scientific research about it crucial. The assessors, after considering the semi-empirical literature, write that: Based on current understanding, only the collapse of marine-based sectors of the Antarctic ice sheet, if initiated, could cause global mean sea level to rise substantially above the likely range during the 21st century. However, there is medium confidence that this additional contribution would not exceed several tenths of a meter of sea level rise during the 21st century. {13.4, 13.5}[emphasis in original] 8. The assessors also differentiate between two major sources that could trigger disintegration of WAIS: surface warming, which causes the formation of meltwater ponds and destabilization on the surface of the ice sheet, and oceanic warming, which would destabilize submarine ice. In summary, the authors conclude that, Based on the limited literature, there is medium confidence that oceanic processes may potentially trigger further dynamical change particularly in the latter part of the 21st century, while there is also medium confidence that atmospheric change will not affect dynamics outside of the Antarctic Peninsula during the 21st century 9. 6 John A. Church, Peter U. Clark, Anny Cazenave, Jonathan M. Gregory, Svetlana Jevrejeva, Anders Levermann, Mark A. Merrifield, Glenn A. Milne, R. Steven Nerem, Patrick D. Nunn, Antony J. Payne, W. Tad Pfeffer, Detlef Stammer, and Alakkat S. Unnikrishnan. Science 20 December 2013: Bamber JL and WP Aspinal An expert judgment assessment of future sea level rise from the ice sheets. Nature Climate Change.Published online January 6. DOI: /NCLIMATE IPCC 2013, IPCC, Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. 4

5 Therefore, there is slightly more concern over oceanic warming than surface warming for triggering collapse in the next century: Global sea level rise is expected through 2100 even if mitigation measures take place soon. Resilience and mitigation planning are now required. Uncertainty remains around the likelihood of WAIS collapse, but such an event could contribute substantially (up to several more decimeters) to the 22-98cm projected globally if it occurs. Implications for the Antarctic The implications of a rapid disintegration of the WAIS are, of course, global. However, ASOC suggests that the ATCPs consider the implications of rapidly changing ice sheet dynamics from multiple perspectives: logistical, environmental, and scientific. Logistically, changes in the ice sheet may result in logistical challenges for operators, including blockages of shipping routes, significant local sea level rise, and salinization of base systems, among others. There may be significant challenges and costs to ice sheet change in the short and long term for Antarctic managers and operations. Environmentally, changes in the ice sheet will lead to other glaciological and ecological changes in the Antarctic. Ice streams may speed up or stall, subglacial lake dynamics may change, bird nesting grounds may be disturbed, traditional migratory or food obtaining routes may be altered or abandoned, to name a few potential changes. ASOC encourages flexible and quick-to-implement management plans to help protect key values and species where practicable, and the implementation of strong monitoring systems at a minimum to ensure that management plans are consistent with the potential new realities that may emerge from drastic glaciological changes. Scientifically, research on the ice sheet is ongoing and supported by many National Antarctic Programs. This research is critical to working towards understanding ice sheet behaviour with more certainty. Additionally, logistics should be put into place to transport scientists to site if dynamical changes start to occur. Deploying rapid research teams will allow for warning and detection globally as well as greatly improved scientific understanding of one of the planet s major glaciological concerns. Policy Recommendations for the ATCM 1) There is a longstanding international scientific consensus about the reality of anthropogenic climate change. IPCC s AR5 underscores this fact and notes that some of consequences of climate change are occurring now, and are accelerating. Framing climate science as a debate is harmful as it limits commonsense policy approaches towards mitigating the effects of climate change and stopping more catastrophic climate events from occurring. ASOC encourages all ATCPs to stop rehashing debates about climate change and start implementing proactive and practical mitigation management strategies in the Antarctic. 2) Antarctic research programs support some of the most important climate research being carried out. ASOC encourages support climate research at current or stronger levels. 3) Where long-term glaciological research is not feasible, Antarctic managers should have both rapid research and rapid response plans in place to cope with potential ice sheet collapse, from a scientific as well as logistical perspective. 4) ASOC supports the ATCPs efforts in producing press communiqués as a public outcome of annual ATCMs, and encourages communications about climate change to use scientific findings from assessments like the SCAR ACCE report and the IPCC assessment report. 5) This IPCC report and other scientific findings generate increasing uncertainty for policy decisions and behooves ATCPs to take a more precautionary approach in enacting conservation of values identified in the Protocol. ASOC urges ATCPs to review current policy decisions, especially with Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Page

6 respect to species protection, environmental impact assessment, and protected area development and management to ensure a deliberately precautionary approach is taken. 6