One of the world's biggest ice masses, the West Antarctic Ice Sheet, could melt over the next few thousand years and raise sea level by as much as 5 meters if nearby ocean temperatures rise by several degrees Celsius, researchers report. Although such a dramatic rise in temperature may seem unlikely in the near term, such conditions are possible based on paleoclimate data and a new computer model, which show that the ice sheet has collapsed multiple times in the past.
Researchers are investigating what warmer temperatures might do to the world's largest ice masses, including the 2-kilometer-thick ice mass that constitutes the West Antarctic Ice Sheet, lying to the southwest of the southern tip of South America. If the ice sheet melts, many of the world's coastal areas, including Bangladesh, southern Florida, and southern Louisiana, could be under water.
Forecasting the ice sheet's behavior has been difficult, however, because over the past million years, global temperatures have been too cool to provide much insight about what might happen in a balmier climate. So, two teams of researchers tried a new approach. One group examined a pristine drill core from sediment below the sea bottom near the ice. In the part of the core that dates back from about 5 million to 3 million years ago, when temperatures and greenhouse gas levels were somewhat higher than they are today, the group found evidence of multiple, 40,000-year cycles of melting and refreezing.
Then the second group compared that data with a new, three-dimensional computer model that simulated the ice sheet's behavior over the past 5 million years. The teams report in two papers tomorrow in Nature that the West Antarctic Ice Sheet could indeed begin to collapse sometime in the next century or so if nearby ocean temperatures increase roughly 5°C--a possibility if current warming trends continue. If that warming occurs, the sheet could totally collapse in a few thousand years but contribute to sea-level rise much sooner.
Geoscientist Richard Alley of Pennsylvania State University, University Park, says the data team has "done an amazing amount of work to reconstruct the history of the [Antarctic] climate and the ice sheet over times that are important, because we may warm to or beyond those conditions under business-as-usual behavior." Likewise, he says, the modelers have "made major advances," though the ice model will need to be combined with an equally sophisticated ocean model to more precisely estimate the melt rate of the ice sheet.