They begin knowing about it a little more about the evolution of the polar floe this summer in the big North. The American Centre of data on the snow and the ice (NSIDC) published on Wednesday its first analyses. The surface of ice of Arctic sea got closer to the historical minimum of last year, without crossing it. Before it begins again growing last week, the floe was 9,4 % more sprawling than last year. On the other hand, it was less of 33 % than the normal calculated over 1979 in 2000. Minimum is attained in September, and the maximum in March of every year.

In 2007, explains NSIDC, during last weeks of the period of cast iron, the ice had been pushed northward by winds, compactant the floe in the high degrees of latitude, and liberating waters more in the south. What is productive difficult to make the part of things between the role of these displacements and the real cast iron. This year, the analyses of movements of the floe show less compact ice, and therefore divided on one more supermarket.

Other parametres allow to explain distance between 2007 and 2008. First of all, it was more cool on the Arctic ocean this year. Besides, the young ice (formed last winter) has been this summer in higher degrees of latitude, and therefore more cold, than the one-year-old ice were noticed in 2007. They therefore less melted. Suddenly, the winter period starts with much more of young ice than last year (on the graph, the age of the ice in September 15th of the dark blue - one year in the red - six years and more).

It remains that these observations do not give long-term indication on the evolution of climate in the Arctic. She indeed assesses on several decades. On this occastion the minimum of floe raised this year registers in the downward trend raised since 1979. But it will be necessary to wait for the launching of satellites capable of measuring the thicknesses of ice to appreciate what takes place in the North Pole and to know the lost volume of ice, or earned, every year. Today, data fragmented, got by air-borne radars and submarines, let think that the thickness drops for several decades. But they concern only a weak part of the Arctic, especially in the zones of shipping. Climatologists and glaciologists wait with impatience that a satellite brings a total vision of situation.

In 2005, the European Space Agency had lost Cryosat, after the fault of a Russian pitcher Rockot. His substitute Cryosat-2 must be thrown in 2009. He will load the altimetre radar SIRAL 2, capable of measuring difference between the height of the ice and the surface of the sea. His mission is envisaged for three years. A too short length to determine the long-term evolution of the floe and of the continental skull caps of ice, but which will allow to fix a point of reference for the future campaigns of observations.

NB. The users of Google Earth will be able to show here the data of NSIDC. A video also gives the evolution of the mimum of Arctic floe from 1979 till 2006

Picture: © NSIDC - University of Colorado at Boulder