Recent news that Arctic winter sea ice bounced back to previous levels after an unprecedented summer melt prompted speculation that the global warming scenario had been exaggerated. Indeed, it’s been a surprisingly cold winter across much of the northern hemisphere — so is there really anything to worry about? Yes, says a new report backed by NASA.
Since the end of December 2007, I’ve written several items concerning the rapidly changing scenario in the Arctic. In particular, on 28th December 2007, scientists reported that the 2007 summer melt of Arctic sea ice had beaten all previous recorded measurements, whereas on 21st February 2008 came news that the apparent expansion of Arctic sea ice during the winter months had been so extensive that the summer’s loss was completely recovered — even surpassed. Some took this to mean that the global warming of recent years could well be nothing more than a blip, a brief anomaly in a greater cycle of natural climate variation.
Now, data released by NASA show that the oldest, thickest Arctic sea ice is under considerable stress. That’s bad news, according to Walt Meier of the National Snow and Ice Data Center (an organisation partly funded by NASA). “Thickness is an indicator of long-term health of sea ice, and that’s not looking good at the moment,” he told reporters on Tuesday 18th March 2008.
There is a layer of long-lived ice known as perennial sea ice — year-round ice cover that remains even when the surrounding short-lived seasonal sea ice melts in summer. According to NASA-processed microwave data, the perennial sea ice has been rapidly declining from year to year: whereas perennial ice used to cover 50 to 60 percent of the Arctic, this year it covers less than 30 percent. Very old ice that remains in the Arctic for at least six years comprised over 20 percent of the Arctic area in the mid to late 1980s, but this winter it decreased to just six percent.
Because Arctic sea ice is already floating in water, it doesn’t raise sea levels as it melts — unlike the effect glaciers melting on Greenland or Antarctica have, because they’re on land — but its loss does contribute to global warming when the white ice that reflects heat from the sun is replaced by dark water that absorbs the sun’s heat energy.
Meier said that some 965,300 square miles (2.5 million sq kms) of perennial ice have been lost — about one and a half times the area of Alaska — a 50 percent decrease between February 2007 and February 2008. He added that the oldest “tough as nails” perennial ice has decreased by about 75 percent this year, losing 579,200 square miles (1.5 million sq kms), or about twice the area of Texas.
This means that in many areas, the stronger perennial ice is being replaced by younger, thinner new ice — ice that’s much more readily disturbed by wind and warm sea temperatures.
The BBC reported Meier saying of an Arctic largely covered with younger ice: “It may look OK on the surface, but it’s like looking at a Hollywood movie set — you see the facade of a building and it looks OK, but if you look behind it, there’s no building there.”
Turning their attention to Antarctica, the scientists found less dramatic change, attributed to the difference in the two polar regions: the Arctic is an ocean surrounded by land, while the Antarctic is a continent surrounded by ocean.
But the scientists did notice dramatic warming on the Western Antarctic Peninsula — warming recently documented in the field by British scientists and on which I reported in a write-up dated 25th February 2008.
Clearly, there’s still much to keep an eye on, both north and south.
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