Arctic researchers have discovered a clue as to why sea ice in the North is melting so much faster than anyone thought it would. Scientists have long puzzled over why Arctic sea ice is retreating at up to three times the rate that climate models say it should. In an effort to answer that question, a group of U.K-based explorers walked more than 500 kilometres of sea ice in the High Arctic, taking temperature readings of the ocean below them. They found a layer of cold, salty water about 200 metres down that they suspect has come from the melting...