| | Datum: | 05.12.05 | | Titel: | BBC Focus, December 2005: IS THE ICE REALLY MELTING? | | Link: | www.focusmag.co.uk/ | | Details1: | IS THE ICE REALLY MELTING?
BBC Focus, December 2005
By David Whitehouse
Recent reports suggest that Arctic sea ice is declining faster than ever. But do we know enough to say what's happening with any certainty?
Recently the news headlines told us that scientists at the University of Colorado had found that the extent of Arctic sea ice - the floating ice that covers the Arctic Ocean - is declining rapidly. Almost everyone said that anthropogenic global warming was to blame and that it was another example of humanity's detrimental effect on the planet.
The data was obtained from a satellite that uses microwave radiation to monitor sea-ice changes. According to Mark Serreze of Colorado University's National Snow and and Ice Data Center, it indicated that in September 2004 sae ice extent (in other words, the ice's surface area) was almost 14 per cent below average. September usually marks the end of the summer melt season when the extent of the ice is at its lowest. Even so, the decline in sea ice extent during September has only been around eight per cent during the past decade. "This is the third year in a row with extreme ice losses, pointing to an acceleration of the downward trend," Serreze told BBC Focus. Researchers say a dip in the September ice extent one year is often followed by a recovery the following year, but that this has not been the cased in the past year. The September 2004 sea ice loss was especially evident in northern Alaska and eastern Siberia.
"One possible explanation for the continuing loss of sea ice is that climate warming from human activities like the burning of fossil fuels is becoming more apparent," says Serreze. "Climate models are in general agreement that one of the strongest signals of greenhouse warming will be a loss of Arctic sea ice."
UK on ice
Some say it's a crisis. According to the University of Colorado's Julienne Stroeve, we may soon reach a 'tipping point' - a threshold beyond which the sea ice can no longer recover. The result would be a runaway loss of ice, leading to an ice-free Arctic in a few decades. This would alter the global energy balance and affect ocean circulation patterns, possibly causing the North Atlantic drift that keeps Britain's shores ice-free, to fail.
Serreze believes natural climate variability likely plays some part in the observed changes. "However, the most reasonable view is that the nice decline represents a combination of both natural variability and the greenhouse effect, with the latter becoming more evident in coming decades," he says.
But scientists need to be careful. The records of ice in the Arctic do not go very far, meaning that researchers cannot be completely sure whether what they see is a result of man or nature.
"It's always difficult with a short period of observations to determine if a trend seen over a short period will continue," climate scientists Professor Duncan Wingham, of University Collage London, told BBC Focus. "We know that Arctic ice has cycles of decline and recovery, but the recent decrease seems considerable. It does seem to be indicative of a larger change than we have ever seen before."
Cryosat coverage
But not all scientists agree that the declining surface area of ice in the Arctic is an indication that the total amount of ice is diminishing. It is known that ice can get thinner in some regions and thicker in others so that even when the total area declines there could be little change in the total volume.
Scientists thought they had a solution to the problem of finding out exactly what was happening to the Arctic ice - in the form of a European Space Agency (ESA) satellite called Cryosat. "Cryosat was designed to improve the data coverage of the Arctic ice and to tell us how much ice ikn total, not just the area of ice, was disappearing from the Arctic," says Professor Wingham.
But disaster struck. Cryosat was launched on a Russian rocket from the Plesetsk complex in Northern Siberia on 8 October. A few minutes after launch it suffered a malfunction and instead of entering orbit crashed onto the very ice it was supposed to monitor. Dismayed scientists say that Cryosat most be rebuilt and relaunched, perhaps as soon as three years from now.
At Liverpool John Moores University, Dr Benny Peiser points out that the Arctic ice is a complex system and that if you look at it in too simplistic a way, you will not be able to draw valid conclusions: "We must be careful in equating a decrease in the quantity in surface ice area with a real decrease in the quantity of ice. There is much variation in growth and decay from year to year and place to place., by as much as a metre in just a few years. Natural variability is considerable. Mankind may not be to blame after all."
Dr David White House is Science Editor of BBC News Online
Copyright, 2005 BBC Focus
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