Global warming cleared on ice shelf collapse rap
Natural causes to blame, expert claims
The high-profile collapse of some Antarctica's ice shelves is likely the result of natural current fluctuations, not global warming, says a leading British expert on polar climates.
This surprising finding is supported by analysis of data from the European Space Agency's ERS-1 satellite, according to Duncan Wingham, Professor of Climate Physics at University College London. The data, measuring changes in ice thickness across the Antarctic ice sheet using the polar orbiting satellite, show areas of growth from snowfall are as common as areas of decline.
This is a contrasting picture to one based solely on the northern Antarctic Peninsula - a shark's fin of land jutting out from the body of the continent, and reaching to just 750 miles from Chile - where there has been a drastic increase in temperature, thinning of ice sheets and collapse of ice shelves. The Larsen A ice shelf, 1600 square kilometres in size, fell off in 1995. The Wilkins ice shelf, 1100 square kilometres, fell off in 1998 and the Larsen B, 13,500 square kilometres, dropped off in 2002. Meanwhile, the northern Antarctic Peninsula's temperatures have soared by six celsius in the last 50 years.
"A lot of attention and research has focused on this relatively accessible area of the Antarctic Peninsula, but satellites are giving us a picture of the continent as a whole," Wingham told the Register. This broader picture shows evidence of growth and decay from place to place, a picture more in line with natural variations in snowfall and ocean circulation. The Antarctic is to some extent insulated from global warming because to its north are zonal flows in the atmosphere and ocean, unimpeded by other landmasses. This insulates the continent from warmer events further north and leads one to suppose it is better protected from global warming.
"Taken as a whole, Antarctica is so cold that our present efforts to raise its temperature might be regarded as fairly puny. Change is undoubtedly occurring: in the collapse of the northerly Peninsula ice shelves, and elsewhere in the West Antarctic Ice Sheet, where the circumpolar current appears to reached the ice edge and is eating away drastically at the ice shelves. One cannot be certain, because packets of heat in the atmosphere do not come conveniently labelled 'the contribution of anthropogenic warming'.
"But the warming of the Peninsula has been going on for a considerable time, and the pattern of regional change is variable, and neither of these is favorable to the notion we are seeing the results of global warming".
At the US station at the South Pole, temperatures have in fact fallen by a degree since 1957. "The Antarctic Peninsula is exceptional because it juts out so far north," Wingham explained.
The professor continued: "I am not denying global warming. For instance, Greenland, in the northern hemisphere, does seem to be going. But Greenland's ice cap - Greeland is quite far south - is a last survivor from the ice age and only its height protects it. The more that cap melts, the more it will continue to melt as it gets lower and warmer. But Antarctica is different. Even in the Arctic I am sceptical of some claims that 40 per cent of the sea ice has already vanished, and that what remains is drastically thinning.
"Sparse data from subs in some parts of the Arctic do seem to show a thinning trend, but our preliminary observations using satellite data point to large growth and decay from year to year and place to place, by as much a meter in just a few years. Here too natural variability is considerable. No one doubts that the ultimate fate of Arctic ice looks a grim one, but I believe we have too few data to be confident of how fast it will meet its fate."
Prof Wingham, who is the Director of the UK's National Environmental Research Council's Centre for Polar Observation and Modelling, spoke to us after a European Union Space Conference in Brussels. He attended in his capacity as the Project Scientist of the European Space Agency's 130M euro "Cryosat" satellite mission, to be launched later this year and dedicated to spotting climate change in the polar zones.
Earlier media reports after a conference on climate change in Exeter suggested it was "unclear" whether the collapse in the Antarctic ice shelves was due to global warming or not. Although the melt and collapse of the ice shelves does not raise sea levels initially, there is fear these shelves act as corks whose disappearance could lead to an outflow from landbased glaciers - which would increase sea levels.