350

It's the most important number in the world. 

http://www.350.org/

350 is the number that leading scientists say is the safe upper limit for carbon dioxide—measured in "Parts Per Million" in our atmosphere. 350 PPM—it's the number humanity needs to get back to as soon as possible to avoid runaway climate change.

We are at about 370 now. Meaning we are all going to die if we don't change this. When I say "all going to die" I mean the human race will cease to exist.