Global warming may be melting glaciers and Antarctic ice more quickly than previously thought, accelerating the threat from rising sea levels, according to two new studies published in this week's Science magazine.

Researchers from the University of Alaska in Fairbanks have determined that glaciers in the state are melting significantly faster than previously believed and contributing more than expected to rising sea levels.

"We're finding that glaciers are thinning much more rapidly than was thought in the past," said Anthony Arendt, the leader of the team that authored the study.

The researchers found that the state's glaciers thinned enough to raise the sea level about 0.14 mm a year between the mid-1950s and the mid-1990s, and an average of 0.27 mm yearly during the past decade. Both amounts were vastly greater than recent models used to predict sea-level rise.

A second study by Columbia University scientists of sharply declining salinity in the Antarctic's Ross Sea over the past 40 years concluded that the melting West Antarctic ice sheet is a major contributor to the freshening of seawater that made its way to the South Pacific.

Previously, researchers believed that increased rain and snowfall in the Antarctic were responsible.

The two studies are certain to add to growing concern about the impact of global warming on the world's oceans.

New theories by oceanographers suggest that substantially larger volumes of fresh water flowing into the oceans could not only increase sea levels — threatening low-lying islands and coastlines — but could also seriously disrupt and even reverse ocean currents such as the Gulf Stream, which warms the waters and climate of the North Atlantic region within very short periods of time.

Irresponsible and short-sighted

The collapse earlier this year of an Antarctic ice shelf the size of the US state of Rhode Island coupled with the fact that the 1990s was the hottest decade in the past century, have increased public concern over climate change here and abroad.

US President George W Bush's withdrawal from the Kyoto Protocol, an international agreement to reduce greenhouse emissions, has increasingly come under attack, particularly after a report released by his own Environmental Protection Agency (EPA) in late May.

It concluded not only that carbon emissions bore most of the responsibility for warming, but also that resulting climate change will "very likely" lead to disruptions in snow-fed water supplies, stifling heat waves, and the disappearance of entire ecosystems within the United States over the next few decades.

A poll released last week found that more than three-quarters of voters, including 65 percent of self-described Republicans, agreed with the statement that doing nothing about global warming is "irresponsible and short-sighted".

The new studies are likely to fuel the debate. They not only tend to confirm global warming but also support predictions by climate models that assume warming is caused by rising concentrations of greenhouse gases emitted by the burning of fossil fuels. Those models predict the polar regions will warm more rapidly than the rest of the world.

The Alaska study is also worrisome in that it suggests the sea level — which has risen on average about 1.5 mm a year over the past century and as much as 3.3 mm a year over the past decade — could rise higher and more rapidly than predicted.

The latest results show that the Alaska glaciers alone accounted for almost 10 percent of sea-level rise in the past 40 years. Although they make up only 13 percent of the total mountain glacier area on Earth, the state's glaciers are responsible for one-half of the increase in the sea level caused by all glaciers, mainly due to their proximity to the coast.

Even fractional rises in sea level can have major impacts. More than 100 million people live within one metre of sea level, and storm surges can devastate coral reefs and low-lying islands and coastlines from the Indian Ocean to the Eastern Caribbean.

"Although some degree of sea-level rise is anticipated in the coming decades, the greater the rise and the faster it occurs, the greater the impact will be on human population," says Benjamin Preston, senior research fellow with the Pew Center on Global Climate Change here.

Other threats

The increasing flow of fresh water from both glaciers and polar ice into the world's oceans also poses other threats, particularly to critical ocean currents, which many scientists believe act as a climate-control mechanism for much of the planet.

The Columbia study, led by Stanley Jacobs of the university's Lamont-Doherty Earth Observatory, used records compiled over 40 years to uncover a sharp decline in the salinity of the water in the Ross Sea, as well as warmer air and water temperatures in the area.

While researchers in the past argued that increased precipitation caused a drop in salinity, the Columbia group found that increased melt water from the West Antarctic ice sheet was also a major factor, and that the melting had accelerated.

That finding comes amid increased attention to the theory that a major increase in the fresh water content of the oceans could block or divert the Gulf Stream, causing air temperatures to plunge as much as 10 degrees Fahrenheit from the eastern coast of North America across the Atlantic to the Baltic Sea, within a decade or even less.

"Although the likelihood of such an event remains highly uncertain," noted Preston, "if scientists have underestimated the amount of fresh water likely to enter the oceans in coming decades, they may have also underestimated the risk of such a phenomenon occurring." — IPS