MELISSA BLOCK, host:
This is ALL THINGS CONSIDERED from NPR News. I'm Melissa Block.
ROBERT SIEGEL, host:
And I'm Robert Siegel.
NASA scientists announced today that 2007 tied the record for the second hottest year in a century. A lot of that warm air was near the North Pole, so it's no coincidence that 2007 was also the worst year on record for melting sea ice in the Arctic. But air temperature is only part of the story, as NPR's Richard Harris reports.
RICHARD HARRIS: Every winter, the Arctic Ocean freezes over with a bed of ice that stretches from Canada to Siberia. Every summer, a lot of that ice melts back, exposing open ocean. Melting sea ice doesn't change sea level, but it does change the environment for polar bears and other wildlife. And for the past decade, the melt back has been getting bigger and bigger. 2007 was a doozie, eclipsing all previous records.
That trend has led Wieslaw Maslowski, at the Naval Postgraduate School in Monterey, to make a bold projection. Soon, he says, virtually all the Arctic Ocean's ice will melt in the summertimes.
Prof. WIESLAW MASLOWSKI (Oceanography, Naval Postgraduate School): If the trend that we've seen through 2007 continues, we probably don't need much more than five to 10 years to actually experience ice-free summers in the Arctic.
HARRIS: At a scientific meeting in San Francisco last month, he mentioned 2013 as the date that could happen. More warming leads to more open water. Water is darker than ice, so more sunlight gets absorbed. And that warming leads to more melting.
Prof. MASLOWSKI: So, we're just pretty much like a snowball going downhill.
HARRIS: But the Arctic Ocean isn't quite so tidy. Take last year's massive ice melt off. Cecilia Bitz, at the University of Washington, says it wasn't just caused by warmer water melting more ice.
Prof. CECILIA BITZ (Department of Atmospheric Sciences, University of Washington): It's normally very cloudy in the Arctic and it was much less cloudy and that let in more sunlight and that caused a lot more sea ice to melt.
HARRIS: And not only do icebergs melt, wind also blows them out of the Arctic Ocean.
Prof. BITZ: We know there's a stream of ice moving out. Something like 10 percent of the ice leaves every year.
HARRIS: Last year, Bitz says odd weather pattern shoved a lot more ice out into the North Atlantic, and that also contributed significantly to the loss of Arctic ice.
Dr. JIM MASLANIK (Research Associate, University of Colorado, Boulder): 2007 was very unique. You had all kinds of situations that came together to make it almost a perfect storm year for lost sea ice.
HARRIS: Jim Maslanik, from the University of Colorado, says next year will almost certainly be not so dramatic, but the long-term trend is still worrisome. He has an article in the latest issue of Geophysical Research Letters, "Looking at What Happened to the Arctic Ice as it Melted."
Dr. MASLANIK: The big change that we targeted was, what's happening to the ice that's remained.
HARRIS: He and his colleagues found that the ice that manages to survive summer is getting thinner and thinner. There's a lot of variation, but in general, ice that used to be 10 feet thick is now just six feet thick.
Dr. MASLANIK: So we have greater potential to lose more and more of the surviving ice because it's thinner to start with.
HARRIS: Eventually, Maslanik says, the Arctic Ocean will probably end up looking like the ocean around Antarctica. The sea ice will form every winter and melt every summer. But because there are so many factors that contribute to ice loss, it's hard to project when that day will come.
Cecilia Bitz and colleagues have run many sophisticated climate forecasts and they show an open Arctic Ocean in the summertime as soon as 2040 and as late as some time beyond 2100.
Prof. BITZ: I will see changes in my lifetime that will be more and more remarkable. But I think it's the future generation that I worry very much for. I think that they will see a planet that we would not recognize in their lifetime.
HARRIS: That is unless we do something dramatic and soon to reduce greenhouse gas emissions. Those emissions don't explain the dramatic year-to-year changes we've seen in the Arctic, she says, but they do seem to drive a long-term trend.
Richard Harris, NPR News.