Professor Chris Rapley, of UCL, said: "With the temperature gradient between the Arctic and equator dropping, as is happening now, it is also possible that the jet stream in the upper atmosphere could become more unstable. That could mean increasing volatility in weather in lower latitudes, similar to that experienced this year."
CryoSat-2 is the world's first satellite to be built specifically to study sea-ice thickness and was launched on a Dniepr rocket from Baikonur cosmodrome, Kazakhstan, on 8 April, 2010. Previous Earth monitoring satellites had mapped the extent of sea-ice coverage in the Arctic. However, the thickness of that ice proved more difficult to measure.
The U.S. probe ICESat made some important measurements of ice thickness but operated intermittently in only a few regions before it stopped working completely in 2009. CryoSat was designed specifically to tackle the issue of ice thickness, both in the Arctic and the Antarctic. It was fitted with radar that can see through clouds. (ICESat's lasers could not penetrate clouds.) CryoSat's orbit was also designed to give better coverage of the Arctic sea.
"Before CryoSat, we could see summer ice coverage was dropping markedly in the Arctic," said Rapley. "But we only had glimpses of what was happening to ice thickness. Obviously if it was dropping as well, the loss of summer ice was even more significant. We needed to know what was happening – and now CryoSat has given us the answer. It has shown that the Arctic sea cap is not only shrinking in area but is also thinning dramatically."
Sea-ice cover in the Arctic varies considerably throughout the year, reaching a maximum in March. By combining earlier results from ICESat and data from other studies, including measurements made by submarines traveling under the polar ice cap, Laxon said preliminary analysis now gave a clear indication of Arctic sea-ice loss over the past eight years, both in winter and in summer.
In winter 2004, the volume of sea ice in the central Arctic was approximately 17,000 cubic kilometers. This winter it was 14,000, according to CryoSat.
However, the summer figures provide the real shock. In 2004 there was about 13,000 cubic kilometers of sea ice in the Arctic. In 2012, there is 7,000 cubic kilometers, almost half the figure eight years ago. If the current annual loss of around 900 cubic kilometers continues, summer ice coverage could disappear in about a decade in the Arctic.
However, Laxon urged caution, saying: "First, this is based on preliminary studies of CryoSat figures, so we should take care before rushing to conclusions. In addition, the current rate of ice volume decline could change." Nevertheless, experts say computer models indicate rates of ice volume decline are only likely to increase over the next decade.
As to the accuracy of the measurements made by CryoSat, these have been calibrated by comparing them to measurements made on the ice surface by scientists including Laxon; by planes flying beneath the satellite's orbit; and by data supplied by underwater sonar stations that have analyzed ice thickness at selected places in the Arctic. "We can now say with confidence that CryoSat's maps of ice thickness are correct to within 10 centimeters," added Laxon.
Laxon also pointed out that the rate of ice loss in winter was much slower than that in summer. "That suggests that, as winter starts, ice is growing more rapidly than it did in the past and that this effect is compensating, partially, for the loss of summer ice." Overall, the trend for ice coverage in Arctic is definitely downwards, particularly in summer, however – a point recently backed by Professor Peter Wadham, who this year used aircraft and submarine surveys of ice sheets to make estimates of ice volume loss. These also suggest major reductions in the volume of summer sea ice, around 70% over the past 30 years.
"The Arctic is particularly vulnerable to the impact of global warming," said Rapley. "Temperatures there are rising far faster than they are at the equator. Hence the shrinking of sea-ice coverage we have observed. It is telling us that something highly significant is happening to Earth. The weather systems of the planet are interconnected so what happens in the high latitudes affects us all."
Intellpuke: You can read this article by the Observer's Science and Technology Editor Robin McKie in context here: www.guardian.co.uk/environment/2012/aug/11/arctic-sea-ice-vanishing