No, I’m not making this up, and it’s not a prank.

“A preemptive strike [by extra-terrestrials] would be particularly likely in the early phases of our expansion because a civilisation may become increasingly difficult to destroy as it continues to expand. Humanity may just now be entering the period in which its rapid civilisational expansion could be detected by an ETI [extra-terrestrial intelligence] because our expansion is changing the composition of the Earth’s atmosphere, via greenhouse gas emissions,” write researchers from Pennsylvania State University and NASA* in a study entitled “Would contact with extraterrestrials benefit or harm humanity? A scenario analysis.”

Science correspondent Ian Sample reviewed the study yesterday in the UK Guardian. A pearl from his article:

“Green” aliens might object to the environmental damage humans have caused on Earth and wipe us out to save the planet. “These scenarios give us reason to limit our growth and reduce our impact on global ecosystems. It would be particularly important for us to limit our emissions of greenhouse gases, since atmospheric composition can be observed from other planets,” the authors write.

Sample shows these speculations the proper respect by posting this picture at the top of his article:

Clearly, the IPPC climate impact assessments are too “conservative” and global warming poses a bigger threat than scientists previously predicted.

The only point I would add to Sample’s knee-slapper of a review is that the “green alien” scienario made its Hollywood debut in the 2008 remake of The Day the Earth Stood Still, starring Keanu Reeves.

In the original 1951 film, Klaatu and his robot Gort come to Earth to deliver an ultimatum: Mankind must end the nuclear arms race and abandon its warlike ways or Earth will be destroyed. In the remake, Klaatu and Gort come to rescue plant and animal species endangered by global warming and to exterminate mankind as punishment for our fuelish ways. Gort pulverizes our fossil-fueled industrial infrastructure and is on the verge of wiping out humanity when Klaatu, moved by the beauty and purity of heart of astrobiologist Dr. Helen Benson (Jennifer Connelly), dies instead for our sins of emission.

* NASA is apparently taking some heat — or at least some good natured ribbing — for this paper. In a recent clarification, one of the co-authors, Shawn Domagal-Goldman, states that the study “isn’t a ‘NASA report.’ It’s not work funded by NASA, nor is it work supported by NASA in other ways.”

He elaborates: “Yes, I work at NASA. It’s also true that I work at NASA Headquarters. But I am not a civil servant … just a lowly postdoc. More importantly, this paper has nothing to do with my work there. I wasn’t funded for it, nor did I spend any of my time at work or any resources provided to me by NASA to participate in this effort.” Domagal-Goldman admits to “making a horrible mistake. It was an honest one, and a naive one… but it was a mistake nonetheless. I should not have listed my affiliation as ‘NASA Headquarters.’ I did so because that is my current academic affiliation. But when I did so I did not realize the full implications that has.”

Lest anyone mistake his apology to NASA for a retraction, Domagal-Goldman adds: ”One last thing: I stand by the analysis in the paper. Is such a scenario likely? I don’t think so. But it’s one of a myriad of possible (albeit unlikely) scenarios, and the point of the paper was to review them.”