But a lot more work remains to be done. "I think it's a very impressive piece of observational analysis," says Del Genio, who wasn't involved in the study. "It's the first time anyone has demonstrated these decadal changes." But, he adds, more modeling will be the only way to back up their tentative conclusions.
Low-level clouds are a difficult target for modeling, Clement admits. "They're forming on a microphysical scale." The Hadley model was probably the most successful, Clement notes, because it had the most information about the complex processes that happen in the lower atmosphere, where it comes in contact with Earth's surface—a zone, Clement explains, that is much more difficult to model than large-scale circulation in the upper atmosphere.
And, as always, there is the question of how one reconciles day-to-day weather events with the long-term climatic trends. As Clement points out, "If you look at the hour-to-hour cloud processes, you get a very complex story." But, "the data, on the decadal time scale, seems to have this very simple story: When the ocean surface is warm and the circulation is weak, the cloud cover is reduced."