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

The world’s best climate models don’t capture the true extent of Earth’s energy imbalances, and scientists don’t know why.

Rather than reflecting actual satellite observations, the model consistently underestimates the growing gap, or imbalance, between the amount of energy Earth receives from the sun and the amount of energy the planet radiates into space, a new study shows. It’s unclear what components are missing that make the model faster, but researchers think it may have something to do with how clouds interact with small particles in the atmosphere known as aerosols.

“Representations of cloud changes in response to changes in aerosols may not fully reflect reality,” Seiji Yukimoto, lead study author and a climate scientist at Japan’s Meteorological Research Institute, told Live Science via email.

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Satellite observations show that the Earth’s energy imbalance has more than doubled in the past 20 years, and has increased particularly rapidly since 2010. Research shows that more energy is trapped in the atmosphere than is released into space, causing temperatures to rise. Most of the energy imbalance is caused by human greenhouse gas emissions, but scientists say other factors are also at play.

In 2023, the imbalance reached 1.8 watts per square meter (0.16 watts per square foot). This was double what climate models had estimated based on increases in greenhouse gas emissions. Models generally show an increase in Earth’s energy imbalance, but the rate varies from simulation to simulation and does not accurately reflect what satellite observations show, Tianle Yuan, an atmospheric scientist at the University of Maryland, Baltimore County and NASA Goddard Space Flight Center, told Live Science in an email.

The researchers attempt to explain this discrepancy by proposing that the simulations may not fully account for feedback processes, natural variability, and reductions in aerosol emissions. To find answers, Yukimoto and his colleagues used 15 state-of-the-art climate models, satellite radiation data, and records of surface temperatures to reconstruct Earth’s energy imbalance from 2001 to 2024.

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

“Their analysis is solid and simple,” said Yuan, who was not involved in the study. “They analyzed various emissions scenarios, but none could fully simulate the observations. They found a failure of the model to capture the large increase in emissions.” [Earth’s energy imbalance]. ”

This failure suggests that the model is missing a hidden mechanism that reduces the amount of energy Earth radiates into space. The study shows that while climate models take greenhouse gases into account, they may not capture the effects that rising surface temperatures have on clouds and other factors that regulate the amount of energy that escapes into space. There are also questions about the impact of aerosols, which have been declining since 2010 due to China’s emissions cuts and new shipping regulations.

High aerosol concentrations produce more and smaller cloud droplets, which reflect more light and energy back into space. Aerosols also affect the lifespan of clouds, Yukimoto said. Therefore, reducing aerosol concentrations in the atmosphere can affect how clouds scatter light and energy.

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“Aerosols are very difficult to influence because they are heterogeneous in type and distribution, and their impact depends on the location and conditions of the affected cloud. [model]” said Yukimoto.

If the sharp increase in global energy imbalance since 2010 was due to a decline in aerosol emissions, the rate of increase should slow as aerosol levels stabilize, Yukimoto said. If the increase was instead due to clouds reacting to rising surface temperatures, the Earth’s energy imbalance would be even greater, potentially warming the planet faster than greenhouse gases alone. However, “our results contradict this,” Yukimoto said.

The gap between observations and models is widening. To get more realistic results, scientists will have access to models that more accurately represent the effects of sea surface temperature and aerosols on clouds, Yukimoto said.

Cloud-aerosol interactions may be the key to modifying models, and several studies support this idea, but uncertainties remain, Yuan said. “It would be great to have more detailed information, such as how the performance of subsets of the model differs, and to drill down into possible causes of model underestimation,” he said.