* Thinner winter ice could mean more summer melting
* Arctic drives global weather
By Deborah Zabarenko, Environment Correspondent
WASHINGTON, Feb 4 (Reuters) - Scant ice over the Arctic Sea this winter could mean a "double whammy" of powerful ice-melt next summer, a top U.S. climate scientist said on Thursday.
"It's not that the ice keeps melting, it's just not growing very fast," said Mark Serreze, director of the U.S. National Snow and Ice Data Center.
In January, Arctic sea ice grew by about 13,000 square miles (34,000 sq km) a day, which is a bit more than one-third the pace of ice growth during the 1980s, and less than the average for the first decade of the 21st century.
Arctic ice cover is important to the rest of the world because the Arctic is the globe's biggest weather-maker, sometimes dubbed Earth's air-conditioner for its ability to cool down the planet.
More melting Arctic sea ice could affect this weather-making process; it is unlikely to lead to rising sea levels, any more than an ice cube melting in a glass of water would make the glass overflow.
If Arctic ice fails to build up sufficiently during the dark, cold winter months, it is likely to melt faster and earlier when spring comes, Serreze said by telephone from Colorado.
"We've grown back ice in the winter, but that ice tends to be thin and that's the problem," he said. "You set yourself up for a world of hurt in summer. The ice that is there is also thinner than it was before and thinner ice simply takes less energy to melt out the next summer."
With less of the Arctic sea covered in ice in winter, and with the existing ice thinner and more fragile than before, "you've got a double whammy going on," Serreze said.
This more perishable thin ice is prone to early melting, and when it does, the heat-reflecting light-colored sea ice is replaced by heat-absorbing dark-colored ocean water, which accelerates spring and summer melting in the Arctic.
This winter, there were unusually warm December temperatures in the Arctic due to a weather pattern known as the Arctic oscillation, so ice grew more slowly than normal.
In January, that pattern shifted to produce cooler Arctic temperatures. The ice extent -- the area the ice covers -- was below normal over much of the Atlantic sector, including the Barents Sea, part of the East Greenland Sea and in the Davis Strait.
There was above-average ice extent on the Pacific side of the Bering Sea, the National Snow and Ice Data Center reported.
The last three years -- 2007, 2008 and 2009 -- had the lowest level of ice extent since satellite records began in 1979. (Editing by Mohammad Zargham)