Chlorophyll

Specifically, that humans are causing, or at the very least accelerating, global climate change. If ever there was any doubt that there is scientific consensus on this, it should be conclusively laid to rest now.

But, no! Not everyone is convinced. In fact, if you're a scientist willing to shoehorn evidence into Exxon Mobil (and the W administration)'s foregone conclusions, you stand to make a nice bundle of money.