Pandemic temporarily warmed the climate

A recently released study finds that curtailed societal activity during the early stages of the pandemic also reduced emissions of pollutants that usually act to cool the climate.

The big picture: Coronavirus measures helped lead to a sharp, if temporary, reduction in greenhouse gases, but some other pollutants actually act to cool the climate — and with emissions of those significantly reduced as well, the climate warmed for a few months.

By the numbers: Temperatures over parts of the Earth's land in spring 2020 were about 0.2–0.5°F warmer than expected, given the prevailing weather at the time, according to a study by scientists at the National Center for Atmospheric Research.

• The effect was particularly pronounced in areas that usually have a lot of aerosol pollution, like the U.S., where temperatures were up 0.7°F above expected levels in much of the country.

Flashback: Some of the defining images of the early months of the pandemic included the sudden appearance of clear skies in usually smog-choked cities like Los Angeles and New Delhi.

• Those pictures were a consequence of coronavirus lockdowns that sharply reduced driving and manufacturing — in other words, the activities that usually lead to pollution.

How it works: While emissions of greenhouse gases like carbon dioxide warm the climate over time because they trap heat in the atmosphere, airborne particles called aerosols released during combustion have the opposite effect, brightening clouds and reflecting heat back into space.

• Fewer aerosols meant less of their cooling effect, which temporarily translated into a warmer Earth.

Be smart: With carbon dioxide emissions down 6.4% in 2020, the ultimate effect of the pandemic will likely be to slow global warming down slightly, as the long-term impacts of less CO2 in the air outweigh the short-term effects of fewer aerosols for a few months.

• But the study's counterintuitive results are a reminder of climate action's time-lag problem.
• It will take 10–20 years before we experience the cooling caused by 2020's drop in CO2 emissions, but the warming effect of reduced aerosols was experienced almost immediately, simply because the two classes of pollutants have vastly different lifespans.

The bottom line: Acting to reduce CO2 emissions now means accepting that the climate benefits will be delayed — and humans aren't great with delayed gratification.