Scientists understand some pollutants keep the planet cooler, but now fear cleaning up the air might be causing global warming to increase much faster than perviously thought.
First published last week in the journal Environment Research Letters, the University of of Texas at Austin assessment is the first to focus on the impact of declining aerosol levels on human exposure to heatwaves.
Using current climate modelling, it is thought that aerosols are 2.5 times more influential than greenhouse gases at driving changes in heatwave occurrence in urban areas. The higher the concentration of aerosols the lower the temperature.
Looking at instances of heatwaves between 1920 and today, the team believe they have identified a reversal of history trends during that time. As air pollution climbed during the first half of the 20th Century, heatwaves were artificially suppressed. But as skies have become cleaner due to tighter regulation, cities are becoming more exposed to temperatures, which are rising faster as carbon emissions remain stubbornly high but the presence of other human-made gases falls.
‘We knew that aerosol emissions were suppressing global warming at the regional level, but the impact of that same suppression on heatwaves near urban centres was much greater than we expected,” said Cameron Cummins, co-author of the University of Texas study. ‘Aerosols are really good at counteracting exposure [to heatwaves] right now, but that could rapidly change in the future. We seem to have already crossed a tipping point where declining aerosols are accelerating heatwave exposure in a lot of places.’
The researchers point to Western Europe as a highly visible example of a region which has historically been saved from the full extent of global warming due to high levels of aerosol. As levels have fallen in the past quarter century, summer temperatures have rocketed, driving heat-related deaths, wildfires and other health risks. According to estimates, the length of heatwaves in this part of the world could extend by 40 days a year as aerosols vanish from the atmosphere.
According to Geeta Persad, an assistant professor at the UT Jackson School of Geosciences who led on the work, there is a danger that this could be taken as a license to pollute in a bid to suppress temperatures. However, with strong links to heart and lung damage, contribute to disease and early mortality, aerosols post an equally grave risk to public health compared with emissions. Nevertheless, changing regulations around aerosols in the near future should take into account how this will impact heatwave and exposure hazards over the next 20 to 30 years.
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