COVID-19 Lockdowns Caused Cleaner Air – And Warmed the Planet

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Research shows reductions in aerosol emissions had slight, temporary warming impact.

The lockdowns and reduced societal activity related to the COVID-19 pandemic affected emissions of pollutants in ways that slightly warmed the planet for several months last year, according to a new study by the National Center for Atmospheric Research (NCAR).

The counterintuitive finding highlights the influence of airborne particles, or aerosols, that block incoming sunlight. When emissions of aerosols dropped last spring, more of the Sun’s warmth reached the planet, especially in heavily industrialized nations, such as the United States and Russia, that normally pump high amounts of aerosols into the atmosphere.

“There was a big decline in emissions from the most polluting industries, and that had immediate, short-term effects on temperatures,” said NCAR scientist Andrew Gettelman, the study’s lead author. “Pollution cools the planet, so it makes sense that pollution reductions would warm the planet.”

Temperatures over parts of Earth’s land surface last spring were about 0.2-0.5 degrees Fahrenheit (0.1-0.3 degrees Celsius) warmer than would have been expected with prevailing weather conditions, the study found. The effect was most pronounced in regions that normally are associated with substantial emissions of aerosols, with the warming reaching about 0.7 degrees F (0.37 C) over much of the United States and Russia.

The new study highlights the complex and often conflicting 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 elevating temperatures.

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

The study was 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 at Oxford University, Imperial College, and the University of Leeds.

Teasing out the impacts

Although scientists have long been able to quantify the warming impacts of carbon dioxide, the climatic influence of various types of aerosols – including sulfates, nitrates, black carbon, and dust – has been more difficult to pin down. One of the major challenges for projecting the extent of future climate change is estimating the extent to which society will continue to emit aerosols in the future and the influence of the 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 nations. They 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 showed that 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 pervasive.

Gettelman said the study will help scientists better understand the influence of various types of aerosols in different atmospheric conditions, helping to inform efforts to minimize climate change. Although the research illustrates how aerosols counter the warming influence of greenhouse gases, he emphasized that emitting more of them into the lower atmosphere is not a viable strategy for slowing climate change.

“Aerosol emissions have major health ramifications,” he said. “Saying we should pollute is not practical.”

Reference: “Climate Impacts of COVID‐19 Induced Emission Changes” by A. Gettelman, R. Lamboll, C. G. Bardeen, P. M. Forster and D. Watson‐Parris, 29 December 2020, Geophysical Research Letters.
DOI: 10.1029/2020GL091805

17 Comments on "COVID-19 Lockdowns Caused Cleaner Air – And Warmed the Planet"

  1. The processes that produce visible pollutants, like smoke and soot, are the same processes that produce invisible ones like CO2. When those processes increase then we are told that the resultant increase in CO2 caused the earth to get warmer. When those processes decrease then we are told the resultant decrease in visible pollutants caused the earth to get warmer. These cannot both be true. The proponents of AGW theory have been telling us for decades that burning fossil fuels would increase atmospheric CO2 and cause runaway warming. The only sure fire way to test this theory would be to drastically reduce fossil fuel use – something they knew was not going to happen – until it actually did. Now they have to explain why the earth continued to warm anyway. Sounds like they were caught with their pants down.

    • Did you read the article? This outcome was predictable and explainable. Aerosols have a strong, but short term light blocking affect. CO2 has a weak, but long term heat trapping affect. This is neither new nor contradictory information.

      “Despite the short-term warming effects, Gettelman emphasized that the long-term impact of the pandemic may be to slightly slow climate change because of reduced emissions of carbon dioxide, which lingers in the atmosphere for decades and has a more gradual influence on climate. In contrast, aerosols – the focus of the new study – have a more immediate impact that fades away within a few years.”

      • The really interesting thing is that studies have been able to document decreases in the atmospheric concentrations of NOx and particulates, and increases in ozone. Anthropogenic emissions of CO2 decreased, YET, there was no discernible decrease in atmospheric CO2 concentrations, or even the rate of increase, at any of the monitoring stations during the time that the CO2 sinks in the northern hemisphere were inactive.

        That raises the uncomfortable question of whether it is reasonable to expect the rate of CO2 increase to decline if we take drastic measures to curtail the use of fossil fuels! An alternative hypothesis to the prevailing paradigm is that anthropogenic emissions are so small, compared to the annual turnover of the Carbon Cycle, as to be negligible! Yet, politicians who have no expertise in science, claim to “believe science” and are willing to risk a major disruption in the economy to support their ‘belief.’ I’d rather see a detailed cost/benefit analysis with estimates of the time necessary to accomplish the steps in the revolution, taking into consideration the availability of essential resources such as copper and Rare Earth Elements. Beliefs are only useful until it becomes obvious that the beliefs are “baseless.”

  2. Harold Bonhomme | February 3, 2021 at 7:52 am | Reply

    What a pile!

  3. “Pollution cools the planet, so it makes sense that pollution reductions would warm the planet.”
    Right, so we’d better can the cleaner vehicle regulations about to be introduced here as it will warm the planet.

  4. Edwin H Hoffmann | February 3, 2021 at 10:42 am | Reply

    I suggest you look at the data on countries with the highest aerosol output, especially PM2.5 which is a global warming driver. Such as:

    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6764381/#:~:text=LMIC%20countries%2C%20such%20as%20China,as%20shown%20in%20Figure%204.

    From the above:

    Top 20 countries based on the decreasing interquartile range of gridded reference PM2.5 mean (in 2010).

    Country Minimum (µg/m3) Maximum (µg/m3) Mean (µg/m3) Median (µg/m3) IQR (µg/m3)
    China 0.39 376.84 30.88 23.07 35.24
    Pakistn 1.82 112.99 23.97 19.31 16.92
    Kuwait 15.39 31.28 22.36 18.87 14.06
    Chad 6.87 53.58 19.04 16.55 13.62
    Niger 8.00 38.76 18.34 17.4 13.61
    Bolivia 0.74 50.4 11.45 12.37 13.14
    India 0.61 71.24 24.19 25.39 11.40

  5. Damned if you do, damned if you dont.
    In america and most advanced nations curtailing emissions offer diminishing returns, the amt of effort and money we put in will only drop pollution slightly while if that money and time is invested in a developing country you will see much greater ROI. Also countries like china which the prev commenter mentions stayed open with little disruptions. While in america we went into full lockdown, in china they had a much stricter lockdown very early on and were virus free thus the whole year they were operating normally with normal level production of pollutants. You may argue their mfg probably went into overdrive picking up the slack from other countries. If this is true then it would highlight that we need to address pollution with developing 2nd 3rd world countries first as that would not only be the low hanging fruit but also give you the best ROI

  6. Chaing Kai Shek | February 3, 2021 at 3:17 pm | Reply

    No worries, SHEENA will get that air pollution back up in no time. The weak, fearful, impotent, and corrupt CCP (with Xiao Winnie the Pooh Xi at its’ ROTTEN core) CREATED the WUHAN virus (think SARS v2.0) to tackle CHINA’s exploding senior citizen population, then tested it at a wet market – overwhelmingly frequented by older shoppers.

  7. Trent Torkelson | February 3, 2021 at 3:22 pm | Reply

    If aerosols are sunlight blockers, and we’re trying to currently curb CO2 emissions, shouldn’t there be also, in addition to the curbing of C)2 emissions, an emphasis on (at least) temporary aerosol increases to stave off the longer term effects of current CO2 levels?

    Was Bill Gates really onto something here?

  8. The US government has funded university studies which found that high altitude spraying of chemical compounds could cool the planet and stop global warming for as long as the spraying was continued. The cost would be about $4 billion a year. Any country with the money could do it. The warming would return soon after the spraying stopped, just like a year after a large volcanic eruption ends. People on the ground would see no difference in the sky because, unlike with a large volcanic eruption, there would be no dust with aerosol spraying. There would be no chance of starting an ice age because the warming would return within a few months of ending the spraying. This isn’t an internet rumor. I saw the scientist who ran one of the government funded studies being interviewed on Al Jazeera TV, while standing on a research ship in San Diego harbor.
    It would be a good plan to stop global warming because, even if we do stop burning fossil fuels TODAY, which we can’t without mass starvation from economic collapse, the warming will continue for at least the rest of this century. That warming to come, if we do no spraying, will continue to raise sea level, displacing billions by the end of this century, and might release enough methane from Alaska, Canada, Siberia, and the sea floor, to start a positive warming feedback loop, which could be catastrophic. There is more carbon in the methane frozen on the sea floor, than in all the world’s other fossil fuels combined! Release that, and humans will be living on a different planet. All coastal cities will disappear, displacing billions of people, and costing hundreds of trillions of dollars. Miami is already starting to go under water. And the rate of sea level rise is increasing. The trillions of tons of carbon dioxide we have already added to the atmosphere will remain there for centuries. And we will continue to add more every day for decades to come. Humans have no choice. We need to work and eat. Poor people want electricity like you have. They want cars too.
    So we need to stop further warming NOW, so that we can buy time to go green, which will take at least the rest of this century. Most countries can’t afford to stop using cheap fossil fuels and switch totally to solar and wind. So despite the promises of their rich elite at fancy conferences in Paris, they won’t switch. Outside the rich world of the US, Europe and Japan, moving away from coal and gas will take a long time. So we have to stop the warming during the long transition away from fossil fuels. Release enough methane from the permafrost, and nothing we could do will be able to stop the runaway warming.
    You have been warned.

    • Bill
      You said, “There would be NO CHANCE of starting an ice age because the warming would return within a few months of ending the spraying.”
      That is a big assumption! One frequently sees claims about the impact of so-called “tipping points” that might dramatically, and effectively irreversibly alter the climate. I might accept “low probability,”; however, I think that “no chance” is a ‘bridge too far.’

  9. Pollution has been targeted as “bad” for years. The Paris Agreement, which is trying to stop pollution by industries across the world is the new golden standard for the world. Now, with Covid, many industries and people across the world have been forced to stop doing business as usual. How are we now changing the narrative that less pollution is causing global warming aka climate change. People need to figure out what they want…

  10. Quite the pile!

  11. A tremendous pile

  12. Holy crap give me a break. This is not scientific reporting. The headline is horrendous and it puts the wrong idea in your head from the start. It looks like they mean to say light warms the ground. More light more warm. Duh. Cold in the shade. Right. Well if we had less droughts due to pollution and climate change we’d have more clouds too. Also wildfire smoke cools the air. Don’t want that. Too many false correlations. This article is stupid and misleading. For shame.

  13. This author switched his stance now saying that pollution creates cooling. Pollution we are told is extra CO2 in the air. And that if that continues it will cause this planet to heat up. Is it because the planet isn’t warming that they are now changing their stance… I mean their scam?

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