In this March 19, 2015, file photo, President Barack Obama, flanked by senior adviser Brian Deese, left, and Christina Goldfuss, managing director of the Council on Environmental Quality, speaks at Energy Department in Washington. In a highly anticipated announcement, the United States will pledge to cut its greenhouse gas emissions by up to 28 percent as its contribution to a major global climate treaty nearing the final stages of negotiation, according to people briefed on the White House's plans. (AP Photo/Jacquelyn Martin)