Arctic Ice Thinner Than Ever Despite Cold Winter
Discover,com, Oct. 7, 2008
Sea ice in the Arctic Ocean has melted to its lowest volume in recorded history, according to new measurements.
At the end of last summer, the seas ice pack melted to the lowest coverage ever, following an exceptionally warm winter. But the winter of 2007-2008 was colder than the last few years have been, and even after this summer's melt season there is still more acreage of ice covering the water than last year.
The problem is, the ice may be thinner than ever.
Walt Meier of National Snow and Ice Data Center in Colorado and colleagues say the overall ice volume in the Arctic Ocean is at least as low as 2007, they say, and may even have dwindled more by as far as 10 percent. Though more widespread than last year, the ice is significantly thinner, Meier said, making it more prone to melting than ever before.
The area of ocean sea ice covers can vary a lot from year to year, so scientists look at ice volume as a long-term indicator of the "health" of the ice. Since satellite measurements began 30 years ago, it has been in steady decline.
"The long term trends in ice volume show a clear trend toward warming temperatures," Meier said. "The health of the ice is at the same state or worse than it was last year."
The latest drop in volume is likely due to a strong wind pattern last year that blew large amounts of thick, multi-year ice south passed the east coast of Greenland, and out of the Arctic Ocean. Because of cold winter, thin new ice formed in its place.
But given the ever-warming waters and air temperatures, Jay Zwally of NASA's Goddard Space Flight Center said the new ice has little chance of making a long term recovery.
"The reason volume is so important is new ice can't get thick enough in the winter to survive next summer's melting," he said. "It takes seven to eight years for sea ice to reach its equilibrium thickness of around four to five meters."
Last December, Zwally predicted that the Arctic Ocean could be seasonally ice free by the end of the summer of 2013, five years from now.
It would be more than just a symbolic milestone of the warming Earth. Pack ice is very good at reflecting sunlight, which protects the water below from warming. As the ice dwindles so does its shielding effect so that the less ice there is, the more quickly the ocean warms.
This factor, called the ice-albedo feedback, figures to exacerbate the effects of global warming, like shifting climate patterns and rising sea level.
The latest measurements are preliminary, though they seem to confirm Zwally's suspicions. However he stressed that scientists will have a better handle on the situation later this year, once the data are in from the ICE Sat satellite, which is currently taking readings of ice thickness from orbit.