Is cleaner air accelerating global warming more than we expected?

Renowned climate scientist James Hansen, famous for his early warnings about global warming, has reiterated concerns about the underestimated impact of declining air pollution on the climate.

During a briefing hosted by the United Nations Sustainable Development Solutions Network, Hansen described the use of aerosols to offset greenhouse gas warming as a “Faustian bargain” that has masked a significant portion of the warming effect.

While Hansen’s research suggests that reductions in air pollution are accelerating global warming, other experts like Michael Diamond from Florida State University caution that these conclusions may be at the higher end of plausibility.

The years 2023 and 2024 saw unprecedented spikes in global temperatures, prompting discussions about the rate of climate change surpassing previous expectations. Hansen and his team attribute this acceleration to the decline in air pollution, particularly focusing on the reduction of sulphur in shipping fuels as a key factor.

By analyzing changes in solar radiation absorption due to decreased air pollution, Hansen’s team estimated that the Earth received an additional 0.5 watts per square meter of heat, equivalent to a decade of current global carbon dioxide emissions. This additional warmth helps explain the unexplained temperature rise in recent years.

Furthermore, the researchers argue that the cooling effect of air pollution has masked the true impact of greenhouse gases, indicating that the climate is more sensitive to emissions than previously thought. This heightened sensitivity could accelerate the onset of critical climate tipping points.

While some experts question the magnitude of the warming effect attributed to changes in aerosols, others like Tianle Yuan from the University of Maryland Baltimore County suggest that the analysis, while ambitious, is not entirely implausible.

NASA’s Gavin Schmidt believes the estimate may be an overestimation, considering other factors like natural variability and changes in emissions from different sources. Additionally, Shiv Priyam Raghuraman from the University of Illinois Urbana-Champaign proposes that changes in Pacific Ocean temperatures alone could explain the temperature spikes without the need to invoke aerosol effects.