"The Arcticís glaciers, including those of Greenlandís vast ice cap, are retreating. The land is thawing: the area covered by snow in June is roughly a fifth less than in the 1960s. The permafrost is shrinking. Alien plants, birds, fish and animals are creeping north: Atlantic mackerel, haddock and cod are coming up in Arctic nets. Some Arctic species will probably die out. Perhaps not since the 19th-century clearance of Americaís forests has the world seen such a spectacular environmental change. It is a stunning illustration of global warming, the cause of the melt. It also contains grave warnings of its dangers. The world would be mad to ignore them. As our special report shows in detail, the Arctic is warming roughly twice as fast as the rest of the planet. Since the 1950s the lower atmosphere has warmed by a global average of 0.7 degrees Celsius; Greenlandís air has warmed by 1.5 degrees. The main reason appears to be a catalytic warming effect, triggered by global warming. When snow or ice melt, they are replaced by darker melt-water pools, land or sea. As a result, the Arctic surface absorbs more solar heat. This causes local warming, therefore more melting, which causes more warming, and so on. This positive feedback shows how even a small change to the Earthís systems can trigger much greater ones."