A new study shows that pandemic lockdowns exerted a slight net warming effect on the planet, but Australian wildfires had a much bigger and faster climate impact, cooling the planet from December 2019 through mid-2020, Andrew writes.
Why it matters: It reveals how two largely manmade forces — the response to COVID-19 and climate change-related wildfires — can influence the planet, with implications for understanding future climate change.
The big picture: When major economies came to a near economic standstill starting early last year, many pollutants were suddenly reduced, including carbon dioxide, but also particulate matter that can reflect incoming solar radiation.
- The clearing of skies over parts of China was observed by satellites, and similar effects followed COVID-related shutdowns in India, Italy and other parts of Europe, and the U.S.
- With reduced economic activity, greenhouse gas emissions declined by 7% in 2020, but only temporarily.
- In the new study, published in Geophysical Research Letters, scientists used advanced computer models to simulate the climate's responses to the COVID-19 pandemic shutdowns.
- The same models were used to analyze the effects of the Australian bushfires of late 2019 and early 2020.
What they found: COVID-related changes in activity exerted a small warming influence through 2022 that can barely be distinguished from natural climate variability.
- But the Australian wildfires, which sent large amounts of particulate matter high into the stratosphere, exerted a "strong and abrupt climate cooling" effect.
- It was significant enough to push the Intertropical Convergence Zone — where air converges just off the equator, forming towering thunderstorms — northward.
- The fires were part of a climate change-linked worsening trend in wildfires in Australia, and they were accompanied by mushroom-cloud-like pyroCb clouds, which helped send smoke high enough in the atmosphere to remain there for months at a time.
- The particles, including sulfate aerosols, contained in the smoke helped modify clouds in ways that enhanced their ability to reflect incoming solar radiation, lead author John Fasullo of the National Center for Atmospheric Research told Axios.
By the numbers: The researchers found the pandemic-related lockdowns will result in an average global warming of about 0.05°C by the end of 2022, whereas the fires cooled the planet in just a few months by about 0.06°C.
- Be smart: The cooling influence of huge wildfires such as the ones in Australia is only temporary, lasting for months to one to two years maximum.
What they're saying: Fasullo said one result from the study is a new appreciation that climate change not only affects wildfire frequency and intensity, but fires themselves create feedbacks that need to be better understood and taken into account.