Can computer models predict climate change?

To accurately depict how individual clouds form and disappear, for instance, the computers that model climate change would need to be a million times faster. For now, the effects of clouds have to be estimated.

But scientists say complexity doesn’t guarantee accuracy. The best test of a model is to check it against reality.

“We’re never going to perfectly model reality. We would need a system as complicated as the world around us,” said Ken Fleischmann, a professor of information studies at the University of Maryland. He said scientists needed to make the uncertainties inherent in models clear: “You let people know: It’s a model. It’s not reality. We haven’t invented a crystal ball.”

Scientists say they don’t need models to know that the world is warming: There is plenty of real-world evidence, gathered since the mid-1800s, to suggest that. “There’s no climate model in that conclusion,” said Christopher Field, of the Carnegie Institution for Science in California.