COVID-19 lockdowns have caused cleaner air – and are warming the planet

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Research shows that reductions in aerosol emissions had a minor and temporary effect on warming.

Closures and reduced societal activity associated with Covid-19 The pandemic affected pollutant emissions in ways that led to a slight warming of the planet for several months last year, according to a new study by the National Center for Atmospheric Research (NCAR).

This inconsequential finding highlights the effect of airborne particles, or aerosols, that block incoming sunlight. When aerosol emissions decreased last spring, more warmth of the sun reached the planet, especially in highly industrialized countries, such as the United States and Russia, which typically pump large quantities of aerosols into the atmosphere.

“There has been a significant reduction in emissions from the most polluting industries, and this has had both immediate and short term effects on temperatures,” said Andrew Gitelman, NCAR scientist, lead author of the study. “Pollution is cooling the planet, so it makes sense that reducing pollution would warm the planet.”

Temperatures over parts of the Earth’s surface last spring were about 0.2-0.5 degrees Fahrenheit (0.1-0.3 degrees CelsiusWarmer than expected with the prevailing weather conditions, the study found. The effect was most pronounced in regions typically associated with large emissions of aerosols, with warming reaching around 0.7 ° F (0.37 ° C) over most of the United States and Russia.

The new study highlights the complex and often conflicting effects of different types of emissions from power plants, automobiles, industrial plants, and other sources. While aerosols tend to lighten clouds and reflect heat from the sun back into space, carbon dioxide and other greenhouse gases have the opposite effect, trapping heat near the planet’s surface and raising temperatures.

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Despite the short-term effects of warming, Gitleman emphasized that the long-term impact of the pandemic may be to slow climate change slightly due to reduced emissions of carbon dioxide, which remains in the atmosphere for decades and has a gradual effect on the climate. In contrast, aerosols – the focus of the new study – have an immediate effect that fades within a few years.

The study was published in Geophysical Research Letters. It was partially funded by the National Science Foundation, the sponsor, NCAR. In addition to the NCAR scientists, the study was co-authored by scholars from the University of Oxford, Imperial College and the University of Leeds.

Stirring up effects

Although scientists were long ago able to determine the warming effects of carbon dioxide, the climate impact of different types of aerosols – including sulfates, nitrates, black carbon, and dust – has been much more difficult to determine. A major challenge for projecting the extent of future climate change is estimating the extent to which society will continue to release aerosols in the future and the effect of different types of aerosols on clouds and temperature.

To conduct the research, Gettelman and colleagues 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 from European countries. They ran simulations on both models, tuned in aerosol emissions and incorporated actual meteorological conditions in 2020.And the Like the wind.

This approach enabled them to quantify the effect of reduced emissions on temperature changes that were too small to be drawn into actual observations, as they could be masked by the variation in atmospheric conditions.

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The results showed that the warming effect was stronger in the middle and upper latitudes of the northern hemisphere. The effect was mixed in the tropics and was relatively negligible in a large portion of the Southern Hemisphere, where aerosol emissions are not diffuse.

Gitelman said the study will help scientists understand the effect of different types of aerosols in different weather conditions, helping to guide efforts to reduce climate change. Although the research shows how aerosols counteract the warming effect of greenhouse gases, it has emphasized that emitting more of them into the lower atmosphere is not a viable strategy for slowing climate change.

“Aerosol emissions have major health implications,” he said. “To say we should pollute is impractical.”

Reference: “Climate Impacts of COVID-19 Induced Emission Changes” by A. Gitelman, R Lampool, CG Bardeen, BM Forster and Dr. Watson – Paris, December 29, 2020 Geophysical Research Letters.
Doi: 10.1029 / 2020GL091805

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