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Why Predicting West Antarctic Ice Sheet Behavior is so Hard: What We Know, What We Don't Know and How We Will Find Out

Robert Bindschadler

One million years of paleoclimatic data tell a consistent and convincing story - a warmer Earth contains less ice. Given that the IPCC Fourth Assessment Report predicts a temperature increase of 1.1-6.4°C over the next century, we can expect the amount of ice on the planet to decrease. Just how fast this decrease will occur, however, is still not well established as scientists are working to understand the mechanisms that control how fast the ice sheets will melt. What we do know is that records of sea level in ancient coral show that, as the ice sheets retreated at the end of the last glaciation, sea level rose at a rate up to 30 times faster than the present rate of rise, suggesting that once ice sheets begin to melt, extended episodes of ice loss can be relatively rapid. Understanding what this would mean for the Antarctic Ice Sheet, particularly the West Antarctic Ice Sheet that is grounded below sea level, is the focus of this chapter.

Sea level rise is very much a 'wild card' when it comes to predicting the effects of climate change. Approximately a third of the world's population lives within about 50 km of the coast, with many living much closer. As a result, any rise in sea level could have significant social and economic consequences that would occur in addition to the environmental impacts. Even a relatively modest rise would begin to inundate low-lying regions, accelerate coastal erosion, increase the vulnerability of coastal cities to hurricanes, storm surges and other extreme events, and begin to force relocation of coastal communities and infrastructure. The cost to those in the US of a 1 m rise in sea level, occurring over a century, has been estimated at approximately US$400 billion (Titus et al, 1991). If the rate of rise is more rapid or occurs in increments as storms pound the coastline, the impacts could be much greater. The rate of future sea level rise remains difficult to predict, largely because the impacts of warming on the behavior of the Greenland and West Antarctic Ice Sheets cannot yet be accurately modeled, makes planning along the world's coastlines particularly problematic.

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