Cleaner skies, hotter Earth: How aerosols shape climate change
Theories suggest that a decrease in aerosols may be accelerating climate change. Does cleaner air speed up global warming?
James Hansen, a well-known climatologist who warned the U.S. Congress about global warming in the 1980s, is once again emphasizing that we might be underestimating the impact of reducing air pollution on the climate. In January 2025, a record temperature rose, sparking a debate about the pace of global warming.
However, other scientists argue that these conclusions are based on uncertain grounds, and we still do not know to what extent the reduction in air pollution contributes to global warming.
Hansen's research team previously linked the increasing pace of global warming with decreasing air pollution levels. Now, they present a new analysis suggesting that reducing pollution might be a key factor in the temperature rise over the past two years. Aerosols from pollution can directly reflect solar radiation and also influence clouds' ability to reflect light.
The 2020 experiment
Researchers focused on the 2020 regulation that drastically reduced the amount of harmful sulfur compounds in shipping fuels. This sudden decrease in pollution over the oceans provided scientists with data to more precisely determine the climate effects of aerosols.
Climate warming is progressing faster than expected
Hansen and his team studied shipping lanes in the Pacific to estimate this effect by measuring changes in solar radiation absorption by the planet in these areas. Their studies indicate that the decrease in shipping aerosols increased the heat reaching the Earth by about 0.4 British Thermal Units per square foot. This is roughly equivalent to the warming effect of a decade of carbon dioxide emissions at the current level.
This additional warming could explain the unexplained portion of the temperature increase over the past two years. However, the implications are broader: it suggests that the cooling effect of air pollution may have been masking the full impact of greenhouse gas warming. Hansen and his colleagues warn that this means the climate is more sensitive to rising greenhouse gas levels than expected.
Potential solutions
Scientists suggest considering methods to cool the planet, such as solar geoengineering. However, not all scientists agree with these conclusions. More data is needed to explain the temperature increase in 2023, and further studies on the warming effects of aerosols are necessary.
