WASHINGTON (AP) — Arctic Sea ice melted this summer to the second lowest level since record-keeping began more than 50 years ago, scientists reported Thursday, mostly blaming global warming.“This is not a random event,” said oceanographer James Overland of the U.S. National Oceanic and Atmospheric Administration. “It’s a long-term change in Arctic climate.”The new measurements were taken by the National Snow and Ice Data Center. It reported the amount of ice covering the Arctic hit its lowest point late last week, covering just 1.67 million square miles.