Is cleaner air accelerating global warming more than we expected?
Reductions in air pollution have helped warm the planet by cutting down on reflective particles in the atmosphere – but researchers still disagree on the size of this effect
By James Dinneen
4 February 2025
Air pollution can have a cooling effect on the climate
Cheunghyo/Getty Images
James Hansen, the climate scientist best known for alerting the US Congress to global warming in the 1980s, has redoubled his warnings that we are underestimating the climate impact of declining air pollution.
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“Humanity made a bad deal, a Faustian bargain, when we used aerosols to offset almost half of greenhouse gas warming,” said Hansen at a briefing hosted by the United Nations Sustainable Development Solutions Network.
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But other researchers say this conclusion is based on shaky foundations, and we still don’t know how much reductions in air pollution are contributing to global warming. Hansen’s conclusions are “hovering around the top end of what we’d consider to be plausible”, says Michael Diamond at Florida State University, who wasn’t involved with the research.
Record spikes in global average temperatures in 2023 and 2024 have spurred debate about whether the pace of global warming is accelerating faster than expected. Rising levels of greenhouse gases and a warming Pacific Ocean drove most of the temperature increase, but other unknown contributors pushed average temperatures even higher than can be explained by those factors alone.
Hansen and his colleagues previously linked the accelerating rate of warming with a reduction in air pollution. Now they offer a new analysis arguing that a decline in air pollution can explain the spike in temperatures over the past two years. Aerosols in air pollution can both reflect sunlight away from Earth directly and affect the reflective properties of clouds – changes in cloud cover have also been implicated as a factor in the heat.
