Global warming may not remain merely global anymore, as a new study suggests its cosmic impact.

Beyond endangering the earthly inhabitants, humans may have posed a serious threat to the entire galaxy, possibly prompting aliens to destroy humanity in order to end global warming and save the rest of the galaxy from being contaminated as well.

Surprisingly, the suggestion comes from one of NASA's scientists.

The scenario was brought up in a joint study by Penn State University and the NASA Planetary Science Division, titled Would Contact with Extraterrestrials Benefit or Harm Humanity? A Scenario Analysis.

A preemptive strike would be particularly likely in the early phases of our expansion because a civilization may become increasingly difficult to destroy as it continues to expand, the study says. Humanity may just now be entering the period in which its rapid civilizational expansion could be detected by an ETI (extraterrestrial intelligence) because our expansion is changing the composition of the Earth's atmosphere, via greenhouse gas emissions.

By using spectrometry, extraterrestrials could detect changes in Earth's atmosphere and deduce that we're out of control, speculated the researchers, among a number of other scenarios discussed in the 33-page paper.

Some scenarios suggest that human contact with aliens would be beneficial, such as how aliens would help us acquire better knowledge and help us solve problems such as hunger, poverty and enable us to eliminate diseases. Another scenario points toward an alliance between humans and Aliens to help us protect ourselves from an attack by other extra-territorial beings.

The neutral scenarios, on the other hand, involve situations in which aliens do not try to communicate with us and prefer to observe us without making any contact.

The harmful scenario, on the other hand, are a bit more dramatic as NASA scientists warn aliens could attack us, enslave us, eat us or spread alien diseases among us or among crucial food species, to destroy us.

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, stated the authors.

Should a hostile group choose open large-scale invasion, we wouldn't see just a few over a city exercising military operations, I believe we would see not just thousands, but tens of thousands of craft landing simultaneously worldwide in order to drop large numbers of their own troops on our soil for military purposes, says UFO Digest in a report.

To prevent these disasters from happening and risk destroying humanity and its future, the document suggest we refrain from sending signals into space, and insist we should especially diminish broadcasts that would provide the potential extraterritorial visitors with information about our biological makeup.

If contact between humans and ETI is possible, then it is important to consider the capability of ETI to cause us benefit or harm. This information is important across nearly the full breadth of contact scenarios, the authors further added. Although we cannot know the level of technological sophistication achieved by ETI, we do have a compelling reason to believe that ETI would be significantly stronger than us and therefore highly capable of causing our total destruction. This point has been raised repeatedly throughout the literature.

Domagal-Goldman, the lead author, later made it clear that the study was not a NASA report and that no NASA funding was expended on it. He also said that his two co-authors, Seth Baum and JacobHaqq-Misra of Pennsylvania State University worked on it.