Researchers have found that the shutdowns of the Covid epidemic in South Asia significantly reduced the number of short-lived cooling particles in the air without affecting the concentration of long-lived greenhouse gases. The scientists were thus able to show how lower air pollution emissions lead to cleaner air, but also to faster global warming.
The study was published in the journal “Climate and Atmospheric Science”. It is well known that emissions of sulfur and nitrogen oxides and other air pollutants lead to the formation of aerosols (particles) in the air, which can offset or mask the overall climate warming caused by greenhouse gases such as carbon dioxide and methane.
However, there is not enough knowledge about this “masking effect”. To determine the size would require large-scale experiments involving huge regions – this is impractical.
The Covid pandemic has become such a “natural” experiment. In the spring of 2020, activity in many industries and transportation around the world decreased due to pandemic restrictions. This created a unique opportunity to study what will happen to the climate if emissions of gases and aerosols are rapidly reduced.
Measuring station in the northernmost Maldives
At Hanimaadhoo, a measuring station in the northernmost Maldives off the coast of India, scientists have been measuring atmospheric composition and radiation for almost two decades. (Measurement Reveals Impact of Air Pollution on Climate and Health in South Asia).
The measuring station is strategically located to capture air masses from the Asian subcontinent and is located in an area with few regional emission sources. When emissions suddenly decreased during the pandemic in South Asia (mainly Pakistan, India and Bangladesh), an opportunity was created to see what impact this had on the climate.
Short-lived particulate matter was reduced, but not greenhouse gases
A new paper in the journal NPJ Climate and Atmospheric Science shows that concentrations of short-lived air pollutant particles dropped significantly, while concentrations of longer-lived greenhouse gases were barely affected in the air mass over South Asia. The cooling effect of aerosols comes from the fact that they reflect incoming solar radiation back into space.
With a lower aerosol content, there is less cooling and thus less “masking” of the warming effect of significantly longer climate gases. Measurements taken at the same time over the northern Indian Ocean revealed a seven percent increase in solar radiation hitting the Earth’s surface, raising temperatures.
“Through this large-scale geophysical experiment, we were able to demonstrate that while the sky became bluer and the air cleaner, climate warming increased when these cooling air particles were removed,” said Professor Orjan Gustafsson from Stockholm University, who is responsible for the measurements in the Maldives and who conducted the study.
The results show that completely phasing out fossil fuel combustion in favor of zero-emissions renewable energy sources could lead to rapid “unmasking” of aerosols while greenhouse gases persist.
“Over several decades, emissions reductions threaten to lead to a net warming of the climate due to the ‘masking’ effect of air particles before the temperature reductions from reduced greenhouse gas emissions become apparent. But despite the initial climate warming effect, we clearly still urgently need a significant reduction in emissions,” said Orjan Gustafsson.
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