North Pole Since 2002, the Russians have also annually established a base, Barneo, close to the Pole. This operates for a few weeks during early spring. Studies in the 2000s predicted that the North Pole may become seasonally ice-free because of Arctic ice shrinkage, with timescales varying from 2016 to the late 21st century or later. The sea depth at the North Pole has been measured at by the Russian Mir submersible in 2007 and at 4,087 m (13,410 ft) by USS "Nautilus" in 1958. The nearest land is usually said to be Kaffeklubben Island, off the northern coast of Greenland about
North Pole will be entirely free of ice in the summer. This may have significant commercial implications; see "Territorial Claims," below. The retreat of the Arctic sea ice will accelerate global warming, as less ice cover reflects less solar radiation, and may have serious climate implications by contributing to Arctic cyclone generation. Polar bears are believed to travel rarely beyond about 82° North owing to the scarcity of food, though tracks have been seen in the vicinity of the North Pole, and a 2006 expedition reported sighting a polar bear just from the Pole. The ringed seal has also been seen at