for National Geographic News
Despite an unusually cold winter, Arctic sea ice is in worse shape than ever, according to the latest satellite observations.
Perennial sea ice—thicker ice that remains frozen throughout the summer—is now at an all-time low, researchers announced at a NASA press conference today.
Arctic sea ice grows through the winter, reaching its largest extent in March. Then it shrinks through the spring and summer, reaching its smallest size in September.
The total area that the sea ice occupies now is not much less than it was a couple of decades ago.
But now, for perennial sea ice, "there's been a real dramatic drop," said Walter Meier of the National Snow and Ice Data Center in Boulder, Colorado.
The amount of perennial sea ice "is essentially an indicator of the long-term health of the ice," Meier said, "and it's not looking very good."
(Explore an interactive of the Arctic's vanishing sea ice.)
Researchers have been closely monitoring Arctic sea ice throughout the year to get a sense of how it's changing, especially as global warming progresses.
Last September the sea ice reached the smallest size ever recorded, showing a whopping 27 percent drop over the previous low, which was set in 2005.
"This drop was a big event, and may be the turning point for Arctic sea ice," said Josefino Comiso of NASA Goddard Space Flight Center in Greenbelt, Maryland.
(Related story: "Arctic Ice Melting Much Faster Than Predicted" [May 1, 2007].)
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