For the first time in perhaps 50 million years, the thick ice covering the North Pole has melted, opening up an ice-free stretch of ocean about a mile wide, according to scientists who recently visited the scene. The melting is being seen by many as further evidence that climate change is upon us. James McCarthy, a Harvard oceanographer and scientist with the Intergovernmental Panel on Climate Change, reported the news after serving as a lecturer on a tourist cruise aboard an icebreaker earlier this month. On a similar cruise six years ago, McCarthy says the ship plowed through ice six to nine feet thick at the North Pole. The Arctic Sea ice cover has shrunk by about 40 percent since the 1950s. Iceland and other Sub-Arctic regions are also warming noticeably.