Tipping point for disintegration?

West Antarctic in red.                                                                        Idiotblogid/Creative Commons

In recent years the West Antarctic Ice Sheet has started to show signs of instability: ice shelves the size of European countries have broken off from coastal areas and glaciers have begun to accelerate into the ocean.

The Antarctic ice sheet covers an area of over 12 million square kilometres (three times the size of the European Union) and is up to 5000 metres thick in places. If it melts entirely, it would raise global sea levels by over 50 metres. While the collapse of the entire Antarctic ice sheet is not considered to be a likely event in the near future, a part of it, the West Antarctic Ice Sheet (WAIS) is attracting interest from the research community as it rests on a bed far below sea level, is directly interacting with the warming ocean, could raise the sea level by 5-6 metres, and is one of the most uncertain elements in modelling climate change in the near future. Over the past few decades, WAIS disintegration was considered a low-probability, high-risk event: something unlikely to happen in the next few centuries, but if it did, could bring devastating environmental and social consequences to much of the world's coastal areas. In recent years, WAIS has started to show signs of instability: ice shelves the size of European countries have broken off from coastal areas and glaciers that were once tucked safely behind the ice shelves have begun to accelerate into the ocean, rapidly thinning parts of WAIS. These events have cast doubts on earlier understanding of WAIS and there is a sense of urgency to update our models and understanding to match reality. The potential for WAIS disintegration in the near term is now considered to be greater than previously estimated. This new view of the ice sheet begs the question: at what temperature would the disintegration of WAIS be inevitable? In other words, what is WAIS' tipping point?

There is a range of estimates for the potential tipping point. Alley and MacAyeal suggested that the WAIS could already be destined for collapse independent of anthropogenic global warming. Newer studies estimate that an irreversible collapse of the WAIS could be triggered if average global temperature rises by 1-5°C above current levels. The existence of such a tipping point would not resolve the question of how fast sea level rise would occur, though a "rapid" disintegration is conventionally considered to occur over one or two centuries. An expert elicitation project in 2002 gave a five per cent likelihood of a rapid disintegration of WAIS within the next 200 years. Katz and Worster updated these estimates and gave a higher likelihood of a rapid disintegration based on recent direct and satellite observations of the WAIS, which show parts of the ice sheet warming, thinning and accelerating. To complicate matters even further, the Antarctic ice sheet is not changing uniformly: for example, some ice streams are accelerating while others nearby are not moving at all.

A future WAIS disintegration remains a highly uncertain phenomenon that researchers are vigorously studying. Even the concept of a WAIS tipping point is still being debated, though most researchers think it would occur if temperatures continue to rise and some suggest it has already been reached, others argue that a "point-of-no-return" model is unrealistic. The research to date, along with predictive ice models, provides results that remain uncertain, but there is no doubt that the WAIS is changing, along with other parts of the world as a response to anthropogenic warming. Precautionary, global action is necessary.

ASOC is a global network of environmental organisations founded in 1978. It holds the only environmental non-governmental seats in the Antarctic Treaty System institutions. It aims to achieve the highest level of environmental protection of the Antarctic region and undertakes activities to proactively address current and emerging threats to the Antarctic environment at national, regional and international levels.

ASOC was instrumental in elevating climate change to a mainstream and crucial item of discussion at the annual meetings of the Antarctic Treaty Consultative Parties, Commission for the Conservation of Antarctic Marine Living Resources, and the Committee for Environmental Protection. In 2005 it began to present high-quality reviews on the state-of-the-art science on Antarctic climate change to draw Treaty Parties' attention to the urgency of climate change. These advocacy efforts have borne fruit and since 2010, climate change has been considered as a subject of high importance at annual meetings of the Antarctic Treaty System institutions.

ASOC has now moved on to advocate for climate change action in Antarctica in line with the rest of the world: mitigation (reduction of greenhouse gas emissions from Antarctic research stations and tourists travelling to and within the Antarctic) and adaptation (protection of the Ross Sea as a climate refugium; and consideration of climate change impacts in the management of Antarctic krill). ASOC's efforts extend beyond the fora of the Antarctic Treaty System, including linking Antarctic climate issues to broader global climate processes like the UNFCC and the IPCC. Its scientific reviews have been submitted to UNFCCC meetings and have been included in publications by the International Union for Conservation of Nature, and the Wildlife Conservation Society. The Ross Sea is one of the world's most important large marine ecosystems remaining in a relatively intact state. It supports internationally important populations of Antarctic wildlife, possesses a unique evolutionary history, and can serve as an important climate change reference area. ASOC proposes a series of steps to fully protect the Ross Sea. At the 2008, 2009 and 2010 ATCM and CCAMLR meetings ASOC introduced detailed information papers on the Ross Sea. The US government introduced papers making the science case for protection prepared by Grant Ballard and David Ainley, ASOC collaborators, at the 2010 meeting of CCAMLR's Working Group on Ecosystem Monitoring and Management.

Tina Tin and Jessica O'Reilley /ASOC

The Future of the West Antarctic Ice Sheet: Observed and Predicted Changes,Tipping Points, and Policy Considerations can be dowloaded at http://asoc.org/storage/documents/ATME/future_of_WAIS.pdf
Read more about climate change and tha Antarctic at: http://asoc.org/issues-and-advocacy/climate-change-and-the-antarctic

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