Warm oceans melting ice sheets faster.

• Position: Greenhouse Effect

Warming of the ocean's subsurface layers will melt underwater portions of the Greenland and Antarctic ice sheets faster than previously thought, according to research led by the University of Arizona, Tucson. Such melting would increase sea levels more than already projected.

"Ocean warming is very important compared to atmospheric warming because water has a much larger capacity than air," explains Jianjun Yin, assistant professor of geosciences. "If you put an ice cube in a warm room, it will melt in several hours but, if you put an ice cube in a cup of warm water it will disappear in just minutes."

Given a midlevel increase in greenhouse gases, the researchers, employing 19 state-of-the-art climate models, found the ocean layer about 650 to 1,650 feet below the surface would warm, on average, about 1.8[degrees]F by 2100. Along the Greenland coast, that layer would warm twice as much, but along Antarctica would warm less--only 0.9[degrees].

Part of the warming in the Northern Hemisphere comes from the Gulf Stream carrying subtropical waters north. By contrast, the Antarctic Circumpolar Current blocks some of the subtropical warmth from entering the Antarctic's coastal waters.

Like rivers of liquid water...