Martin Kettle For nearly a century, human visitors to the North Pole have found a frozen, featureless scene covered in thick ice. Until now. Earlier this month, a group of international scientists aboard a Russian ice-breaker arrived at the pole to find not ice but a stretch of open water at least 1km wide, with ivory gulls flying overhead. Since Robert Peary led the first expedition to the top of the world on foot, no one has ever before found a watery pole, or birds flying in the Arctic air, and it is 50- million years since scientists can be certain that the pole was last definitively awash. “It was totally unexpected,” said Dr James McCarthy, a Harvard University oceanographer. “There was a sense of alarm. Global warming was real, and we were seeing its effects for the first time that far north.” Six years ago, when he last sailed to the pole in an ice-breaker, McCarthy recalled, the vessel ploughed through an ice cap between 2m and 3m thick at the pole. On his latest visit, the ice-breaker crunched its way through kilometres of unusually thin ice. Scientists could see through the ice to plankton which were able to grow in unaccustomed sunlight. When the ship reached the pole, water was lapping its bows. The Russian captain of the Yamal told McCarthy that he had made the voyage to the pole 10 times in recent years and that he had never before encountered the open sea. The scientists’ discovery appears to present some of the most tangible evidence possible that global warming is a real phenomenon. Over the past century, the surface temperature of the globe has risen by less than 1C, though the rate of increase has accelerated in the past 25 years. Strong evidence of the shrinking of the polar ice cap is not new. Scientists at Nasa’s Goddard Space Science Institute, who have compared data from submarines taken in the 1950s with more recent findings, have shown that the ice cover over the entire Arctic area has shrunk by around 45%. Satellite images have confirmed that the extent of the ice cap has been reduced. Most scientists say this is partly the result of the release by industry of heat-trapping gases into the atmosphere. A declining number say the phenomenon is purely cyclical. But in the light of the discovery at the North Pole, scientists say it will be hard for sceptics to go on claiming the problem does not exist.