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.
Read my Climate Change posts in chronological order by using the Climate Change Log.
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The team drove skidoos over the ice for thousands of kilometres taking measurements as they went, using radar and boreholes. The last time this area was visited by scientists was in 1961. More recently, satellites have been used to track changes. According to those measurements, the glacier was accelerating by around 1% a year throughout the 1990s. Julian Scott’s sensational finding this season is that “The measurements from last season seem to show an incredible acceleration, a rate of up to 7%. That is far greater than the accelerations they were getting excited about in the 1990s.”
Julian Scott hopes to figure out whether what’s been recorded is an exceptional surge or whether it heralds a major collapse of the ice, and he’s left some GPS measuring instruments behind on the glacier. The BAS researchers say that if the glacier continues to race along, discharging most of its ice into the sea, the PIG alone could raise global sea levels by 25cm (9.8 inches). That might take quite a while — perhaps decades, or even a century, they suggest — but neighbouring glaciers are accelerating too. If the entire region lost its ice, global sea levels would rise by 1.5 metres (59 inches).
It was 656 feet (200 metres) thick, had an area of 1,255 square miles (3,250 sq. km) and weighed around 500 billion tonnes. In March 2002, the Larsen B ice shelf broke apart. This was not an entirely unexpected event — in 1998, researchers from the British Antarctic Survey had predicted that several ice shelves around the western peninsula were doomed because of rising temperatures in the region, but they were shocked at the speed with which Larsen B collapsed. At the time the reason seemed to be Antarctic summer heatwaves linked to global warming, pure and simple. But now Neil Glasser of Aberystwyth University in Wales and Ted Scambos of the USA’s Colorado University have claimed, in a new study, that it had been teetering on the brink of collapse for decades, and that glaciological and atmospheric factors were also invoved.
Meanwhile, at the other end of the world, a huge fracture in the Beaufort sea ice pack is causing concern amongst scientists. Discovered this winter, the fracture could be a sign of things to come as climate change continues to warm the Arctic, says David Barber, a climate scientist with the University of Manitoba. First discovered in December, the fracture occurred in the Beaufort ice pack off the west coast of Banks Island in Canada’s Northwest Territories.
“It’s the first time we’ve seen it happening so dramatically like this because we lost so much ice last summer,” Barber told