NASA employs fools..so does Pennsylvania State University. I'm sure this article is not an indictment of everyone working for these organizations; but, what these people are saying is stupid.
On second thought, they may have been joking, and it's the U.K.'s the Guardian that is making a fool of itself in the interest of promoting fear over global warming.
Most Econ 101 students should be able to provide one compelling reason why aliens are not likely to destroy the human race to prevent us from spreading greenhouse gasses to other planets....what would that reason be? Go!!
Here's my guess: a race advanced enough to make interstellar travel reasonable (in terms of how long it takes to go from solar system to solar system) is probably advanced enough to have an energy source other than those that emit greenhouse gasses. Or, they may still use such sources, but use it very efficiently. So, rather than conduct a military operation, they might just shoot us a quick email about how to improve our energy usage (I'm assuming a race whose first instinct is to blow stuff up, including entire species and planets, probably wouldn't last long enough to achieve space flight...they might...but I doubt it.