Greenhouse gases

NASA

A University of Washington researcher may have helped solve a Martian mystery by explaining how the chilly surface of Mars could have once flowed with water.

Pictures of Mars clearly show features that look like valleys and old lakebeds, suggesting liquid water once churned on the planet's surface. And yet that surface is really cold, at -80 degrees Fahrenheit, on average.

Steve Liptay Photo

This Saturday, environmental activist and author Bill McKibben will lead a rally against fossil fuel exports and the Keystone XL pipeline in Seattle. 

Known as one of the first voices to warn of the dangers of global warming, McKibben is on tour with his new book, Oil and Honey. He is also the founder of an international organization called 350.org, which he created to fight climate change. 

McKibben says 350 is "the most important number in the world, but nobody knew it until 2008, when Jim Hansen and his team at NASA published a paper saying we now know enough about carbon to know how much in the atmosphere is too much." 

Ever wondered who the big greenhouse-gas emitters are in your neck of the woods? The answer is now just a click away.

The US Environmental Protection Agency today unveiled a new website that identifies most of the nation's biggest emitters of carbon dioxide, methane and other greenhouse gases. It lets you, for example: