Global warming threatens Greenland, study says

Emissions may melt ice-sheet in 1,000 years

April 08, 2004|By Bryn Nelson | Bryn Nelson,NEWSDAY

The rise of worldwide carbon dioxide emissions could virtually eliminate Greenland's massive ice-sheet and swamp coastal communities with 23 feet of sea water in as little as 1,000 years, according to a climate modeling study by a trio of European researchers.

At that height, oceans would likely cover much of low-lying areas such as Florida, Bangladesh and the Netherlands.

A permanent loss of the ice cover on Greenland could be triggered by a rise in the island's average year-round temperature of 5.4 degrees Fahrenheit or more, the study suggests, an effect precipitated by increasing emissions of carbon dioxide and other greenhouse gases into the atmosphere.

"Even if atmospheric composition and the global climate were to return to pre-industrial conditions, the ice-sheet might not be regenerated, which implies that the sea-level rise could be irreversible," the scientists write in today's issue of the journal Nature.

Climate modeling studies have traditionally carried a number of uncertainties, and the latest study is no exception. But lead author Jonathan Gregory, a climate scientist at the Hadley Centre for Climate Prediction and Research in the United Kingdom, said the "real possibility" of the ice loss represents "a severe consequence, so that is something one should think carefully about."

Scientists consider carbon dioxide the main greenhouse gas contributing to global warming, and pre-industrial levels of the gas have been estimated at 280 parts per million, while current levels stand at about 370 parts per million. Most climate studies have predicted a rise in gas levels to beyond 450 parts per million by mid-century.

In all but one of the resulting 35 scenarios in Gregory's study, Greenland's average annual temperature climbed by more than 4.9 degrees Fahrenheit, compared with temperatures in 1990.

After this threshold, past studies indicate, snow melt exceeds snowfall, initiating a contraction of the ice sheet. And beyond a 5.5-degree temperature rise, models have predicted shrinkage to the degree that only residual mountain glaciers would remain. This point of no return, the study suggests, could lead to irreversible sea level increases. The most extreme scenarios envision temperature gains of 14 degrees or more and a virtual meltdown in as little as 1,000 years.

The study contains several caveats, however. Experts say summer temperature increases - instead of average annual increases - are most relevant to the question of Greenland's ice melt since no melting would occur in the frigid winter air.

Michael Oppenheimer, a professor of geosciences and international affairs at Princeton University, said the study's findings are consistent with past conclusions. But Woods Hole Oceanographic Institution physical oceanographer Raymond Schmitt said he is skeptical because the climate models used don't adequately account for ocean warming and heat capacity, so the amount of temperature change could be overestimated.

Nevertheless, Gregory said the study suggests actions taken in the next few decades could have profound implications for sea level changes far into the future.

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