The newest generation of global climate models is running hotter than earlier versions, with many models predicting stronger future warming than their predecessors.

It‘s a confusing trend, and scientists have been working to figure out why it‘s happening. A review paper out this week suggests that clouds—and the tiny particles that help them form in the atmosphere—have something to do with it.

For the past several years, researchers have been working on an international project known as the Coupled Model Intercomparison Project, or CMIP. Every few years or so, modelers around the world coordinate to develop a new generation of models for use in climate research, always more advanced than the generation that came before.

The newest suite…