Associated Press: British explorers in northern Canada to measure the thickness of floating Arctic sea ice ended their expedition short of reaching the North Pole due to an early summer ice melt, the team said Thursday. Explorers Pen Hadow, Ann Daniel and photographer Martin Hartley had planned a three-month journey to the North Pole, but ended their arduous trek Wednesday, approximately 304 miles (490 kilometers) from their destination, said Hadow. The trio stopped after 73 days, during which …