Jeff Bezos’ $10 billion commitment to fight climate change, which he announced last week, brings to mind an episode of “South Park” that aired during the financial crisis. A succession of characters put their money into the market only to see it go instantly to zero before their eyes.

Based on the best science, or at least the most officially condoned, Mr. Bezos would have only the vaguest idea what he was getting for his money. That’s because scientists can estimate only within a giant, squishy margin of error how much warming…