From the desperate files: Aliens may destroy earth because of Global warming

Watching from afar, extraterrestrial beings might view changes in Earth's atmosphere as symptomatic of a civilization growing out of control – and take drastic action to keep us from becoming a more serious threat, the researchers explain.

This highly speculative scenario is one of several described by a Nasa-affiliated scientist and colleagues at Pennsylvania State University that, while considered unlikely, they say could play out were humans and alien life to make contact at some point in the future.

Shawn Domagal-Goldman of Nasa's Planetary Science Division and his colleagues compiled a list of plausible outcomes that could unfold in the aftermath of a close encounter, to help humanity "prepare for actual contact".

http://www.guardian.co.uk/science/2011/aug/18/aliens-destroy-humanity-protect-civilisations