A new study published this month in “Geophysical Research Letters” shows that lockdowns and reduced factory output caused by the COVID-19 global pandemic led to a global warming phenomena around the planet. The study shows that pollution typically cools the planet and the lack of pollution due to the decreased human activity actually lead to global warming during the observed period in 2020.
“There was a big decline in emissions from the most polluting industries, and that had immediate, short-term effects on temperatures,” said Andrew Gettelman, a senior scientist at the National Center for Atmospheric Research (NCAR) and lead author of the new study. “Pollution cools the planet, so it makes sense that pollution reductions would warm the planet.”
According to the published report, when emissions of aerosols dropped in the spring of 2020, more of the Sun’s warmth reached the planet, especially in heavily industrialized nations like the United States and Russia that normally pump high amounts of aerosols into the atmosphere. An aerosol is a suspension of fine solid particles or liquid droplets in the air; they can be natural or anthropogenic. Examples of natural aerosols are fog, mist, and dust while examples of anthropogenic aerosols include particulate air pollutants and smoke.
Aerosols at the surface are known to create health problems. Chronic smog in Beijing, especially during the winter months, is famous for its poor air quality. However, the lack of aerosols documented by this study correlated with a rise in temperatures. According to the published report, temperatures over parts of Earth’s land surface last spring were about 0.1-0.3 degrees Celsius (or 0.2-0.5 degrees Fahrenheit) warmer than would have been expected with prevailing weather conditions.The study found that the effect was most pronounced in regions normally associated with substantial emissions of aerosols, with the warming reaching about 0.37 degrees Celsius (0.7 degrees Fahrenheit) over much of the United States and Russia.
This study used two of the world’s leading climate models: the NCAR-based Community Earth System Model and a model known as ECHAM-HAMMOZ, which was developed by a consortium of European nations. Study authors ran simulations on both models, adjusting emissions of aerosols and incorporating actual meteorological conditions in 2020 such as winds. This approach enabled them to identify the impact of reduced emissions on temperature changes that were too small to tease out in actual observations, where they could be obscured by the variability in atmospheric conditions. The results show the warming effect was strongest in the mid and upper latitudes of the Northern Hemisphere. The effect was mixed in the tropics and comparatively minor in much of the Southern Hemisphere, where aerosol emissions are not as common.
NCAR was established by the National Science Foundation in 1960 to provide the university community with world-class facilities and services. Today, NCAR provides the atmospheric and related Earth science community with state-of-the-art resources including supercomputers, research aircraft, computer models, and an extensive library of data sets.