Close Encounters of the Worst Kind

It may not rank as the most compelling reason to curb greenhouse gases, but reducing our emissions might just save humanity from a pre-emptive alien attack, scientists claim.

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.
~ from Aliens May Destroy Humanity to Protect Other Civilizations, Say Scientists by Ian Sample ~

I have often wondered, if there is intelligent life beyond this planet, what such beings would think of this tortured species called humans. Would they laugh at us? Would they be scared of us? Would they view us as a diseased organism?

If they had intelligence far superior to ours, I would think they would surmise that we are suicidal. We are going out of our way to trash the one home we share. We know how to stop or remedy most of the problems we are causing, but, on the whole, we have shown little interest in doing so. From afar, it might look like we are intent on killing ourselves.

Not only are we suicidal, but we're also homicidal. Our actions will doom countless other species and life forms. We appear to be intent on taking everything else down with us.