Research shows that reductions in aerosol emissions had slight, transient warming.
The lockdowns and reduced social activity associated with the COVID-19 According to a new study from the National Center for Atmospheric Research (NCAR), pandemic has affected pollutant emissions in a way that slightly warmed the planet for several months last year.
The counterintuitive finding highlights the influence of airborne particles, or aerosols, that block incoming sunlight. When aerosol emissions decreased last spring, more of the sun’s heat reached the planet, especially in highly industrialized countries such as the United States and Russia, which normally pump large amounts of aerosols into the atmosphere.
“There was a big drop in emissions from the most polluting industries, and that had immediate, short-term effects on temperature,” said NCAR scientist Andrew Gettelman, the study’s lead author. “Pollution is cooling the planet, so it makes sense that reducing pollution would warm the planet.”
Temperatures over parts of the Earth’s land surface were about 0.2-0.5 degrees last spring Fahrenheit (0.1-0.3 degrees Celsius) warmer than expected with prevailing weather conditions, the study found. The effect was most pronounced in regions normally associated with significant aerosol emissions, with warming reaching about 0.7 degrees F (0.37 C) in much of the United States and Russia.
The new study highlights the complex and often contradictory influences of different types of emissions from power plants, motor vehicles, industrial facilities and other sources. While aerosols tend to brighten 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 increasing its temperature.
Despite the short-term warming effects, Gettelman stressed that the long-term consequences of the pandemic could be to slow climate change somewhat due to reduced carbon dioxide emissions, which linger in the atmosphere for decades and have a more gradual impact on the climate . In contrast, aerosols – the focus of the new study – have a more direct impact that fades within a few years.
The study is published in Geophysical Research Letters. It was funded in part by the National Science Foundation, NCAR’s sponsor. In addition to NCAR scientists, the study was co-authored by scientists from Oxford University, Imperial College and the University of Leeds.
Plague the consequences
While scientists have long been able to quantify the warming effects of carbon dioxide, the climatic influence of different types of aerosols – including sulfates, nitrates, carbon black and dust – is more difficult to determine. One of the biggest challenges in predicting the magnitude of future climate change is estimating the extent to which society will continue to emit aerosols in the future and the influence of different types of aerosols on clouds and temperature.
To conduct the research, Gettelman and his co-authors 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 countries. . They performed simulations on both models, adjusted the aerosol emissions and included the current meteorological conditions in 2020, like wind.
This approach allowed them to identify the impact of reduced emissions on temperature changes that were too small to tease into actual observations, where they could be obscured by the variability in atmospheric conditions.
The results showed that the warming effect was strongest in the middle and upper latitudes of the Northern Hemisphere. The effect was mixed in the tropics and relatively minor in much of the southern hemisphere, where aerosol emissions are not as widespread.
Gettelman said the study will help scientists better understand the impact of different types of aerosols in different atmospheric conditions, informing efforts to minimize climate change. While the research illustrates how aerosols counteract the warming impact of greenhouse gases, he emphasized that releasing more of them into the lower atmosphere is not a viable strategy to slow climate change.
“Aerosol emissions have major health consequences,” he said. “Saying we have to pollute isn’t practical.”
Reference: “Climate Impacts of COVID-19 Induced Emission Changes” by A. Gettelman, R. Lamboll, CG Bardeen, PM Forster and D. Watson-Parris, December 29, 2020, Geophysical Research Letters.
DOI: 10.1029 / 2020GL091805