When I first heard about climate change, I knew that there were essentially three things that needed to be proven.<p>1) That climate change is happening, i.e. the world is getting warmer.
2) That it's not a natural phenomenon, i.e. driven by human behavior.
3) That it's a bad thing, i.e. not a positive thing for the world.<p>Fairly quickly I accepted 1) based on the evidence. Over time I accepted 2), again based on evidence, but mostly on CO2 levels which I knew were well correlated with warm periods historically and logically should be, given it's a green house gas.<p>Much later I started to accept 3). I still think the negatives are over-done, an ice age is far worse than global warming and we have no idea how close we are to the next one. But species extinction simply can't be fixed after the fact, so preventing it trumps all.