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Antarctic May Cause Global Sea-Level Rise

Dr David Whitehouse

Global sea levels could rise by about 1.4 m by 2100 if Antarctic ice melts according to a review of climate change in the continent carried out by the Scientific Committee on Antarctic Research (SCAR.) This is twice as much as predicted two years ago (IPCC: 0.59 m) due to ocean expansion at higher temperatures, glacier and sea-ice melt.  The report says that the IPCC underestimated how much the melting of the Antarctic and Greenland ice sheets would contribute to total sea-level rises.

Determining how the Antarctic will evolve over the next century is fraught with difficulties and uncertainties. We have only a poor understanding of the mechanisms at work responsible for the changes observed there in the past few decades. This is especially true for the ocean where there are very few substantial time series of measurements.

It is against this background that projections of the evolution of the Antarctic climate over the next 100 years must be seen. So called coupled atmosphere-ocean-ice models are utilised but such models have severe difficulty in reproducing the changes that have taken place there already let alone predicting what will happen decades in the future.

The report predicts significant surface warming over Antarctica during the Twenty First Century, an increase of the annual average surface temperature of 0.34°C/decade over land and grounded ice sheets.  Due to the retreat of the sea ice edge induced by global warming, should it resume, the largest projected surface warming occurs during the winter when the sea ice extent approaches its maximum, e.g. 0.51 ± 0.26°C/decade off East Antarctica. Despite this large increase of temperature, the surface temperature by the year 2100 will remain below freezing over most of Antarctica and therefore will not contribute significantly to melting.

The report says, “The climate of the high latitude areas is more variable than that of tropical or mid-latitude regions and has experienced a huge range of conditions over the last few million years. The snapshot we have of the climate during the instrumental period is tiny in the long history of the continent, and separation of natural climate variability from anthropogenic influences is difficult. However, the effects of increased greenhouse gases and decreases in stratospheric ozone are already evident.”

“The effects of the expected increase in greenhouses gases over the next century, if they continue to rise at the current rate, will be remarkable because of their speed. Removal of the cooling effect of the ozone hole as it diminishes in extent will exacerbate the problem. We can make reasonably broad estimates of how quantities such as temperature, precipitation and sea ice extent might change, and consider the possible impact on marine and terrestrial biota. We cannot yet say with confidence how the large ice sheets of Antarctic will respond, but observed recent rapid changes give cause for concern – especially for the stability of parts of West Antarctica.”