Increases in greenhouse gases, especially CO₂, causes the Earth to warm. Although the physics of global warming is well understood, scientists have been uncertain about exactly how much warming to expect from increases in CO₂ and other greenhouse gases. The largest source of this uncertainty is how clouds will respond as the climate warms - clouds are complex and can respond to a warming in complex ways which likely amplify the warming caused by greenhouse gases, but by an uncertain amount.

In a stable climate, the Earth emits as much energy into space as it receives from the sun. However, as greenhouse gas concentration increases, this balance is changing. Satellite measurements since 2001 clearly show significant changes in both solar radiation absorbed by the Earth and the outgoing thermal radiation from Earth. Climate models are an important tool for understanding how the atmosphere including clouds, respond to the warming from greenhouse gases. The latest generation of climate models still have a relatively large range in the amount of global warming we can expect from the same increase in greenhouse gas concentration.

A new study led by CICERO Center for International Climate Research, with co-authors from NASA Langley Research Center and Priestley Centre for Climate Futures (University of Leeds), shows that climate models that give a low warming from increases in greenhouse gases do not match satellite measurements. This means that models with a stronger warming response to greenhouse gas increases are more realistic. In the paper now published in Science, the authors highlighted that this in turn will increase estimates of global warming this century if the world continues along its current emission trajectory. Future warming will likely be worse than thought unless society acts.