Antibiotic resistance, giant mosquitos [1], mutant rats [2]. Pests are evolving to continue living despite our pesticides. We aren't going to make the Earth too hot to live on, or block out the sun with pollution. We're going to be forced off of the planet by evolved pests and predators.

Like species which were forced out of the water, onto dry land, because they were out-competed -- one of our evolutionary advantages is that we can survive in space.

[1] http://www.gainesville.com/article/20130305/ARTICLES/1303098...

[2] http://www.thenational.ae/news/world/middle-east/iran-deploy...