Yale Environment 360: President Barack Obama has rejected a Canadian companys request to build the Keystone XL Pipeline, which would have carried 800,000 barrels of oil a day from Albertas tar sands to refineries on the U.S. Gulf Coast. The decision is a major victory for climate and conservation groups and burnishes Obamas legacy in the battle to slow global warming. Obamas announcement, made after a seven-year review by the U.S. State Department and other agencies, comes just weeks ahead of key United Nations climate...