HOUSTON -- Arctic sea ice in winter is melting far faster than before, two NASA studies reported yesterday, a new and alarming trend researchers say threatens the ocean's delicate ecosystem.
Scientists point to the sudden and rapid melting as a sure sign of man-made global warming.
``It has never occurred before ," said Josefino Comiso, a senior research scientist with the National Aeronautics and Space Administration, in a phone interview. ``It is alarming. . . . This winter ice provides the kind of evidence that it is indeed associated with the greenhouse effect."
Scientists have long worried about melting Arctic sea ice in the summer, but they had not seen a big winter drop in sea ice, even though they expected it. For more than 25 years, Arctic sea ice has diminished in winter by about 1.5 percent per decade. But in the past two years the melting has occurred at rates 10 to 15 times faster. From 2004 to 2005, the amount of ice dropped 2.3 percent; and over the past year, it has declined by 1.9 percent, according to Comiso.
A second NASA study by other researchers found the winter sea ice melt in one region of the eastern Arctic has shrunk about 40 percent in just the past two years. This is partly because of local weather, but also because of global warming, Comiso said.
The loss of winter ice is bad news for the ocean because this type of ice, when it melts in summer, provides a crucial breeding ground for plankton, Comiso said. Plankton are the bottom rung of the ocean's food chain. ``If the winter ice melt continues, the effect would be very profound, especially for marine mammals," he said.
The ice is melting even in subfreezing winter temperatures because the water is warmer and summer ice covers less area and is shorter-lived, Comiso said. Thus, the winter ice season shortens every year and warmer water melts at the edges of the winter ice more every year.
Scientists and climate models have long predicted a drop in winter sea ice, but it has been slow to happen. Global warming skeptics have pointed to the lack of ice melt as a flaw in global warming theory.
The findings are ``coming more in line with what we expected to find," said Mark Serreze, a senior research scientist at the National Snow and Ice Data Center in Boulder, Colo. ``I hate to say we told you so, but we told you so," he added.