A new analysis of nearly 20 years of satellite data shows that this growing energy imbalance has less to do with air pollution than previously thought. Changes in cloud reflectivity play an important role.
This is the conclusion reached by researchers at the Rosenstiel School of Marine, Atmospheric and Earth Sciences at the University of Miami. The work was published in the journal Science Advances and lasted from 2003 to 2023.
Aerosols—tiny particles in the atmosphere from industrial pollution, wildfires, and volcanic eruptions—can affect the climate. They change the properties of clouds and the amount of sunlight reflected into space. However, new research shows that at the global level, their influence has been almost neutral in recent decades.
In the Northern Hemisphere, stricter environmental regulations have led to reduced aerosol concentrations. Fewer particles mean fewer reflective clouds and more solar energy reaching Earth's surface.
In contrast, in the Southern Hemisphere, the contribution of natural aerosols has increased. The massive Australian bushfires of 2019–2020 and the 2022 eruption of the Hunga Tonga–Hunga Ha'apai volcano caused clouds to become “brighter” and more reflective, sending more sunlight into space.
These opposing effects largely offset each other, resulting in the overall contribution of aerosols to the increase in energy imbalance being very small.
Research shows that the key factor is not a decrease in Earth's thermal radiation but an increase in its ability to absorb solar energy. Over two decades, the planet begins to accumulate about 0.5 additional watts of energy per square meter per decade.
To assess the changes, scientists used two independent methods: satellite observations of sunlight streaming through the atmosphere and reanalysis of the data combining measurements and climate models. Both methods showed the same picture – aerosols decreased in the north and increased in the south with no discernible global impact.
Study lead author Chanyoung Park said the findings help shift the focus of the debate: the main cause of accelerating warming is related to changes in cloud cover due to surface warming and natural climate change, rather than improved air quality.
This is also important for climate models. Many models focus on reducing pollution in the Northern Hemisphere and may underestimate the increasing impact of natural aerosol events in the Southern Hemisphere.
“Energy imbalance is a marker of how rapidly temperatures are rising in the climate system,” said co-author Professor Brian Soden. “If aerosols are generally in balance with each other, then we need to look much closer at cloud behavior to understand why the Earth continues to warm.”
In other words, the planet is warming not because the air is getting cleaner but because the clouds are doing less well as a global mirror.
