A report compiled by researchers at Pennsylvania State University suggests global warming may result in an alien invasion. The speculative report claims aliens may attack Earth because they see climate change and population growth as a sign humans are a civilization now out of control. According to the report, referenced in The Guardian, researchers speculate problems on Earth compounded by global warming could attract aliens and spur a possible invasion to bring an end to our troubled civilization.Before panic sets in, it should be noted that the report in question is really a paper written by a couple of friends at the university. One author of the report has a connection to NASA. This fueled speculation that the report was written at the request of the space agency. The university has since clarified that the report has no affiliation with NASA. This is not the first time the topic has been discussed. In June, a Russian astronomer claimed humans will likely encounter some form of alien life by 2031. Earlier this year, it was reported scientists are actively scanning nearly 90 planets for signs of extraterrestrial life.In other space-related news, the recent retirement of the U.S. space shuttle fleet could result in a shortage of manpower for ongoing projects such as the International Space Station. A report released Wednesday by a non-profit group that offers advice on science policy echoes these concerns. Currently, Russia is the only country with a vehicle capable of reaching the ISS. Last month, Russia delayed a planned trip to the ISS due to problems with their space vehicle. This raised additional concern over getting supplies and astronauts to and from the space station. While not officially confirmed, there are some reports that NASA could is considering running the space station unmanned once the current batch of astronauts return to Earth.At the height of the NASA manned space program in 1999, there were 150 astronauts on staff at the space agency. That number is now at 61. The agency has set a goal of 55 to 60 active astronauts on staff through 2016. The agency hopes that by that time private firms will have developed vehicles capable of taking humans into space again. NASA has not abandoned plans for manned missions though. The agency is eying 2025 or beyond as an initial target date for a manned mission to Mars or a nearby asteroid. The National Research Council report warns that an astronaut shortage could leave the agency with astronauts who are not trained as well as they should be for future manned missions.