Remember both tails:

Make of climate models what you may, there is lots of evidence that a) biodiversity is being hammered, and b) climate change will bring desertification, drought, and possibly coastal flooding to many parts of the world, among other dilemmas.  I don’t have a lot of faith in the exact predictive powers of climate models, or for that matter economic models, but uncertainty about outcomes should make us worry more not less.  Uncertainty usually has two tails, not just one.