NEW YORK (AP) President Barack Obama will impose even steeper cuts on greenhouse gas emissions from U.S. power plants than previously expected, senior administration officials said Sunday, in what the president called the most significant step the U.S. has ever taken to fight global warming..... Obama, in a video posted to Facebook, said the limits were backed up by decades of data and facts showing that without tough action, the world will face more extreme weather and escalating health problems like asthma."Climate change is not a problem for another generation," Obama said.