Associated Press: The U.N. climate chief praised President Barack Obama’s pledge to tackle global warming and expressed hope Friday that the U.S. policy shift would boost chances for a new international agreement on cutting emissions of greenhouse gases. “It’s been a night-to-day change in terms of the U.S. position on this topic,” United Nations climate chief Yvo de Boer said in Tokyo, adding that he hopes that the more active American approach will encourage China and other developing nations to make …