and, michael oppenheimer, a climate scientist at princeton university and a member of un panels thatissued reports about climate change. we welcome you both back to the program. coral davenport to you, first, why is the president doing this now? >> the president really wants to use these last two years of his term to build a legacy on climate change. he knows that he can't move anything through congress. he tried that in his first term and it failed. now with the new republican congress, any kind of legislation is d.o.a., so he's turned to the power of the clean air act, an existing law under which he can put out regulations to govern pollution from different sectors of the economy. we've seen him move forward on regulations on emissions from vehicles and power plants, so this is is another piece to have the economy, he's going to sector by sector to rein in emissions wherever they are. so these methane emissions from oil and gas wells, the oil and gas sector are a big piece of the nation's greenhouse gas pollution. >> woodruff: so michael oppenheimer, help us understand why methane