Brussels, 06 Mar 2006
One of the paradoxes of the global warming phenomenon will be an increase in the number of dry and cold winters in Europe, according to an advanced climate model developed by the Alfred Wegener Institute (AWI) and the GKSS (Forschungszentrum Geesthacht) - both members of the German Helmholtz Institute. Meanwhile, US research suggests that the West Antarctic ice-sheet is indeed melting, adding some 0.2mm to global sea-levels per year, while in Africa, a third study shows increasingly polarised weather. All three studies map changes in an ever warmer world.
In both the Arctic and Antarctic, the huge icy surfaces efficiently reflect the Sun's energy back into space. This reflectivity, or 'albedo', means that the ice warms much less quickly than surfaces not covered by ice. If the ice begins to melt, the albedo drops, creating a negative-feedback loop as the surface absorbs more heat, causing more melting, causing the albedo to drop further and so on.
The researchers believe that this drop in albedo is influencing the operation of the North Atlantic Oscillation (NAO), the five to six year fluctuation in air pressure in the north Atlantic, and primary driver of weather patterns in Europe. 'This global pattern of air pressure and temperature distribution has changed drastically during the last five decades. This resulted in significantly warmer winter and slightly cooler summer periods,' said the AWI's Professor Klaus Dethloff.
'Detailed analysis of the first nine years of simulations showed that though warming may occur in the midaltitudes, Arctic cooling will result from a polar vortex churning cold air from the Rockies northward. This indicated that the Arctic exerts a strong influence on the middle- and high-latitude climate,' reads the paper, published in the February edition of Geophysical Research Letters. 'Moreover, the improved parameterization revealed Arctic Oscillation-like fluctuations in the middle troposphere and in middle latitudes that can strongly affect European climate.'
A second study, published in Science has been measuring the thickness of the Antarctic ice-sheets using gravitational information from the Gravity Recovery And Climate Experiment (GRACE) satellites. The two satellites have measured differences in gravity across the planet, which has been useful in obtaining figures for ice melt.
The satellites travel 220 km apart, measuring the gravitational pull of the Earth to an unusually high accuracy. Pictures published in 2003 showed a 'lumpy' earth, with stronger pull in areas of greater mass, such as the Himalayas, and less pull in areas of lower mass, such as the Pacific Ocean.
When looking specifically at the ice sheets in Greenland and particularly the Antarctic, the team found that the Antarctic loses 152 cubic kilometres per year, mostly in the West Antarctic. The only drawback of the system is that it is not sensitive enough to pinpoint exactly where changes are taking place, although accuracy will increase by the end of the mission, currently scheduled for 2009.
The system has accounted for the paradoxical data from the Greenland ice sheet, which suggested that the middle of the sheet was growing while the edges were receding - as the atmosphere warms, the outlying glacier melts, but there is more precipitation, falling as snow, in the centre.
A third study, again published in Science and carried out by a team in South Africa, has found that if rainfall drops by as much as ten per cent, then stocks of ground water could drop by up to 25 per cent by the end of the century. The effects would not be generalised, however, with warm regions becoming warmer and wetter regions becoming wetter.