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A concerning rise in ‘energy imbalance’ is fuelling global warming, as the Earth is taking in more energy than it releases back into space.
A new study led by scientists at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science finds that recent changes in air pollution are not the main reason for an increase in this imbalance.
Aerosols—tiny airborne particles from sources such as pollution, wildfires, and volcanoes—can affect how clouds form and how much sunlight Earth reflects back to space. While aerosols can influence climate regionally, the new research shows their recent global impact has been small.
Published in the journal Science Advances, the study—titled ‘Negligible Contribution from Aerosols to Recent Trends in Earth’s Energy Imbalance’, analysed nearly two decades of satellite observations combined with modern atmospheric reanalysis data. The researchers found that aerosol changes have affected the climate in opposite ways in the two hemispheres.
In the Northern Hemisphere, cleaner air in heavily industrialised regions has reduced the number of particles that help clouds reflect sunlight, allowing more solar energy to reach the Earth’s surface. In contrast, the Southern Hemisphere has seen large increases in natural aerosols from events such as the 2019–2020 Australian wildfires and the 2022 Hunga Tonga–Hunga Ha’apai volcanic eruption. These particles made clouds brighter and more reflective, sending more sunlight back to space. Together, the opposing effects largely cancel each other out, resulting in little net global influence from aerosols on the Earth’s rising heat imbalance.
The study also shows that the recent increase in Earth’s energy imbalance is driven mainly by changes in reflected sunlight, rather than by changes in heat escaping to space. From 2003 to 2023, Earth gained heat at a rate of about half a watt more energy per square meter each decade, largely because the planet is absorbing more sunlight.
To track how aerosols are changing over time, the researchers used two independent indicators. One came from satellites that observe how aerosols in the air affect the passage of sunlight through the atmosphere. The other came from reanalysis data, which combine observations and models to estimate sulphate particles produced by pollution, volcanoes, and wildfires. Despite their different approaches, both methods revealed the same pattern—declining aerosols in the Northern Hemisphere and increasing aerosols in the Southern Hemisphere—indicating that aerosols have had little overall effect on the global energy trend.
The findings also highlight a potential limitation in some climate modelling studies, which focus mainly on pollution reductions in the Northern Hemisphere and may underestimate the growing influence of natural aerosol events in the Southern Hemisphere.
“Earth’s energy imbalance tells us how fast heat is building up in the climate system,” said Brian Soden, a co-author of the study and a professor in the Department of Atmospheric Sciences at the Rosenstiel School.
“Many earlier studies suggested that cleaner air might explain much of the recent increase, but our results show that aerosol changes largely cancel out between the Northern and Southern Hemispheres. That means we need to look more closely at changes in clouds and natural climate variability to understand why the planet is continuing to gain heat,” he added.
The authors of the study include Chanyoung Park and Brian Soden of the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science.
*Curated from the study in Science Advances journal and various news sources.
