US President Barack Obama delivers remarks at a Clean Power Plan event at the White House in Washington, DC, August 3, 2015. President Barack Obama described climate change as one of the key challenges of our time Monday as he announced the first ever limits on US power plant emissions. As a step to try to adapt, Obama announced power plant owners must cut carbon dioxide emissions by 32 percent from 2005 levels by 2030. AFP PHOTO/JIM WATSON (Photo credit should read JIM WATSON/AFP/Getty Images)