Natalie Wolchover, Life’s Little Mysteries Staff Writer

Date: 19 August 2011 Time: 03:11 PM ET

An artist’s illustration of a potential alien attack as depicted in the science television series “Into the Universe with Stephen Hawking.” CREDIT: Discovery Channel/Darlow Smithson Productions Ltd. View full size image

If or when intelligent extraterrestrials discover us, it’s anybody’s guess what they’ll do. They might befriend us. They might eat us. As Carl Sagan once noted, they might find amusement in some talent we have that they lack and use us as entertainment, just as we keep sea lions in captivity because of their remarkable ability to balance rubber balls on their noses.

All of these scenarios and more are fleshed out in a new article in the journal Acta Astronautica by researchers at Pennsylvania State University. One possibility they’ve raised has garnered more attention than any other: An extraterrestrial civilization might notice our planet by detecting changes in the spectral signature of Earth — the light radiated by our planet and atmosphere — caused by greenhouse gas emissions. And they might frown upon our behavior.

The group’s thinking goes like this: From the rate of change of the chemical composition in our atmosphere, the aliens will deduce our rapid expansion and, because of that, possibly view us as a threat, thinking we’ll soon pursue resources on other worlds

to read more, go to:    http://www.space.com/12686-aliens-attack-earth-global-warming.html