The way clouds cover the Earth may be changing because of global warming, according to a study published Monday that used satellite data to track cloud patterns across about two decades, starting in the 1980s.Clouds in the mid-latitudes shifted toward the poles during that period, as the subtropical dry zones expanded and the highest cloud-tops got higher.These changes are predicted by most climate models of global warming, even though those models disagree on a lot of other things related to clouds, says Joel Norris, a climate scientist at the University of California, San Diego. 

Here is a pop quiz: How many trees are on the planet?Most people have no idea.A new study says the answer is more than 3 trillion trees — that's trillion with a T, and that number is about eight times more than a previous estimate.Thomas Crowther was inspired to do this tree census a couple of years ago, when he was working at the Yale School of Forestry and Environmental Studies. He had a friend who was working with a group with an ambitious goal: trying to fight global warming by planting a billion trees. A billion trees sounded like a lot. But was it really?