Ice sheets, namely the Greenland and the West and East Antarctic Ice Sheets store 75 per cent of the planet's fresh water - enough to raise sea level by approximately 65 m. Data from ocean sediment cores and from cores drilled through the ice sheets themselves are providing a rich trove of information about past behavior of the ice sheets. The record indicates that, over the roughly hundred thousand-year cycle of Pleistocene ice ages (the Pleistocene is the geological epoch covering the last glacial period from about 1.8 million to about 11,000 years ago), there have been repeated, slow build-ups of ice sheets, followed by relatively rapid retreats. Ice sheet waning by accelerating ice flow is an easy explanation for the asymmetric behavior, but the details of when, where and how this happens are far from adequately understood, and this is particularly troubling. The time histories suggest that what matters most is what is happening around the edges of the ice sheets. It appears that the dynamics of ice sheet movement, processes that are at present poorly represented in ice sheet models, are the likely mechanisms behind rapid retreat and that, once initiated, these processes rapidly overwhelm the potential for ice build-up from any increase in snowfall rates.
While evident in the geological and cryospheric record, any credible skill in models of reproducing or predicting these dynamic processes remains absent, although achieving skill is currently the main focus of research by many groups. So far, the IPCC assessments have suggested that the pace of change will be modest and smooth, even though glacial history suggests that there could be meltwater pulses and relatively rapid change.
Until recently, the lack of data from the polar regions has meant that scientists had only a rough idea of how the ice sheets would respond over extended periods to climate change. Now better access to these areas for scientific expeditions and new observations from near-polar orbiting satellites have helped show scientists the complexity of the polar environment and how it is already responding to climate change.
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