Earth's energy imbalance is much more extreme than climate models show ‪—‬ but scientists aren't sure why

The world's best climate models are not capturing the true extent of Earth's energy imbalance, and scientists aren't sure why.

Instead of mirroring real-life satellite observations, the models consistently underestimate a growing gap, or imbalance, between the amount of energy Earth receives from the sun and the amount the planet radiates into space, a new study shows. It's unclear what missing component would bring the models up to speed, but researchers think it could be related to how clouds interact with small particles in the atmosphere known as aerosols.

"The representation of cloud changes in response to aerosol changes may not fully reflect reality," study lead author Seiji Yukimoto, a climate scientist in Japan's Meteorological Research Institute, told Live Science in an email.

Satellite observations show that Earth's energy imbalance has more than doubled over the past two decades and risen especially fast since 2010. More energy is being trapped in the atmosphere than is expelled into space, driving up temperatures, according to the study. Human emissions of greenhouse gases are to blame for most of the energy imbalance, but scientists say there are other factors at play.

In 2023, the imbalance reached 1.8 watts per square meter (0.16 watts per square foot), which was twice what climate models estimated based on rising greenhouse gas emissions. Models in general show an increase in Earth's energy imbalance, but the rate differs between simulations, and they never mirror exactly what satellite observations show, Tianle Yuan, an atmospheric scientist at the University of Maryland, Baltimore County and NASA's Goddard Space Flight Center, told Live Science in an email.

Researchers have tried to explain this discrepancy by proposing that the simulations may not fully account for feedback processes, natural variability and declines in aerosol emissions. To find answers, Yukimoto and his colleagues reconstructed Earth's energy imbalance between 2001 and 2024, using 15 state-of-the-art climate models, satellite radiation data and surface temperature records.

The results, published Feb. 22 in the journal Geophysical Research Letters, confirm that some processes in the climate system are missing from the models. The simulations underestimated the amount of energy that Earth absorbed from the sun, particularly between 2010 and 2024, when satellite data shows that Earth's energy budget was completely out of whack.

"Their analysis is solid and straightforward," said Yuan, who was not involved in the study. "They analyzed different emission scenarios and none can fully simulate the observations. They find a failure of models to capture the strong increase in [Earth's energy imbalance]."

This failure suggests that the models are missing hidden mechanisms that are reducing the amount of energy Earth radiates into space. Climate models account for greenhouse gases, but they may not capture the effect that rising surface temperatures have on clouds and other elements that regulate how much energy escapes into space, according to the study. There is also a question regarding the influence of aerosols, which have declined since 2010 due to cuts in China's emissions and new shipping regulations.

High aerosol concentrations lead to more abundant and smaller cloud droplets, which reflect more light and energy into space. Aerosols also affect the lifespan of clouds, Yukimoto said. Thus, falling aerosol concentrations in the atmosphere may influence how clouds scatter light and energy.

"Aerosols are heterogeneous in type and distribution, and their effects vary depending on the location and conditions of the affected clouds, making them extremely difficult to [model]," Yukimoto said.

If the sharp increase in Earth's energy imbalance since 2010 is due to cuts in aerosol emissions, the rate of increase should decline as aerosol levels stabilize, Yukimoto said. If, instead, the increase is from clouds reacting to rising surface temperatures, Earth's energy imbalance could grow bigger and warm the planet faster than greenhouse gases alone could. But "our results contradict this," Yukimoto said.

The gap between observations and models is widening. To get more realistic results, scientists could get the models to more accurately represent the impact of sea surface temperatures and aerosols on clouds, Yukimoto said.

Cloud-aerosol interactions may be the key to fixing the models, and several studies support this idea — but uncertainties remain, Yuan said. "It would be nice to get more details such as how subsets of models perform differently and dive into the possible causes of this underestimation by models," he said.