While we may debate the finer points of how climate change may interact with ice sheets, the general understanding that if our planet warms, ice sheets and glaciers will retreat and sea levels will rise, is not widely contested. It is clear from the geological records that this close connection between

5 Essentially, their hypothesis is that increasing circulatory winds in the Southern Ocean draw more warm water onto the Antarctic continental shelf, and provide more heat for ice sheet melt ing. However, a shortage of marine monitoring sites means that this is difficult to pin down with any real confidence.

temperature and sea-level has been maintained through many glacial cycles. And it is also clear that ice sheets contain the potential to raise sea-level at rates that are many times higher than those we have observed in recent decades. However, the overriding questions regarding the rate that ice sheets will contribute to sea level in coming centuries will remain unresolved until we attain a substantially improved understanding of ice sheet behaviour. The geological record of past changes is a guide in this regard, but today's ice sheets cannot be expected to respond to future anthropogenic change exactly as it did to past natural variations. The contrasting configurations of the Greenland and Antarctic ice sheets mean that they occupy subtly different positions within the climate change debate, both of which have been described as representing tipping points.

The way that the risk that ice sheets pose is perceived is an area that is also worth brief consideration. Studies of risk perception show that they many identifiable factors amplify the social importance and fear surrounding particular risks [18]. These include: the longevity of the risk; its apparent invisibility; and its potential to cause catastrophic events (rather than impacting a few individuals at any one time). As described in this chapter, each of these factors applies strongly to the threat of sea-level rise from ice sheet. Ice sheets may produce effects that, as with nuclear waste, many future generations will have to live with; they are so remote that they can be viewed as essentially invisible, and recent coastal flooding events, for example in New Orleans, have shown the huge scale and severity of the impacts that may become all the more frequent in future. All these factors may serve amplify the perception of the risk and to exert a powerful influence on the public and policymakers alike, but this does not mean that the risk does not exist, or can be ignored, and it is clear that a substantial number of scientists see sea-level rise as a worrying adjunct to the wider climate change debate, and an area where the scientific understanding that underpins predictions is particularly lacking.

We know immeasurably more about current changes in the ice sheets of Antarctica and Greenland, than we did even a decade ago, but it is arguable that this increase understanding has actually increased our uncertainty. Whereas the ice sheets could once be ignored as sleeping giants, there is now evidence they are becoming restless.

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