With a lower aerosol content, there is less cooling, and thus less "masking" of the warming effect of the significantly longer-lived climate gases.
The Covid pandemic shutdowns in South Asia greatly reduced the concentration of short-lived cooling particles in the air, but barely affected the levels of long-lived greenhouse gases, leading to stronger climate warming, a study shows. In the spring of 2020, the activity of many industries and transportation worldwide decreased due to pandemic restrictions.
At Hanimaadhoo, a measuring station in the northernmost Maldives off the coast of India, researchers have been measuring the atmospheric composition and radiation for two decades. The measuring station is strategically placed to capture air masses from the Asian subcontinent and located in an area with few regional emission sources.
When emissions suddenly decreased during the pandemic in South Asia -- mainly India, Pakistan and Bangladesh -- an opportunity was created to see what impact this had on the climate. The study, published in the journal npj Climate and Atmospheric Science, found that the concentrations of polluting short-lived air particles decreased significantly, while the levels of longer-lived greenhouse gases were barely affected in the air.
The cooling effect of the 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 the significantly longer-lived climate gases. Measurements taken at the same time over the northern Indian Ocean revealed a seven per cent increase in solar radiation reaching the Earth's surface, thus increasing temperatures, the researchers said.
"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 at Stockholm University in Sweden, who led the study.
The results show that a complete phasing out of fossil fuel combustion in favour of renewable energy sources with zero emissions could result in rapid "unmasking" of aerosols, while greenhouse gases linger.
"During a couple of decades, emission reductions risk leading to net climate warming due to the 'masking' effect of air particles, before the temperature reduction from reduced greenhouse gas emissions takes over," said Gustafsson. "But despite an initial climate warming effect, we obviously still urgently need a powerful emission reduction," the scientist added.