The papers authors mention a number of factors that may counteract a runaway melting cycle. One is that the extra absorption of sunlight may be less than feared because the maximum area of open water occurs at the end of summer, when the days are already shortening and there is usually ample cloud cover to reflect light anyway. Another, they think, is that once the summer is over, new ice grows fastest where the ice cover is thin or non-existent to start with.

　　Meanwhile, in San Francisco, Dr Pfirman and her colleagues warned against complacency. They noted that CCSM3 does not do a good job of describing the rapid decline of the ice in the last decade. And since the reduction of greenhouse gases is not coming along as quickly as the Nature paper would have it, it seems wise to start treating the refuge area as a precious resource - for instance by keeping new shipping lanes in the Arctic as far from it as possible.

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