The computer models that predict climate change may be overestimating the cooling power of clouds, new research suggests. If the findings are borne out by further research, it suggests that making progress against global warming will be even harder.

The new paper, in the journal Science, focuses on what are known as mixed-phase clouds, which are found around the world and contain both cooled water and ice crystals.

The balance of water and ice in clouds affects the impact that carbon dioxide levels have on atmospheric temperatures, a factor known as equilibrium climate sensitivity. A higher sensitivity would mean that carbon dioxide levels would cause more warming than previously thought.

Using data from instruments aboard the Calipso satellite, which monitors clouds and particles suspended in the atmosphere, the researchers determined that mixed-phase clouds contain more water and less ice than expected.