by A.N. Archer & J.Weber, Oct 22, 2020 in Phys.Org

Countries across the world took unprecedented action in the first few months of 2020 to control the spread of COVID-19. At its peak, one-third of the world’s population was in lockdown. Around the world, car travel fell by 50%, the number of flights plummeted by 75% and industrial activity fell by around 35%.

With so many cars parked, airplanes grounded and factories closed, global carbon dioxide (CO₂) emissions fell by around 17% compared with the same period in 2019. But greenhouse gases such as CO₂ weren’t the only emissions to fall, and not all pollution heats the planet. Some of the industrial activities that shut down—particularly heavy industry, including steel and cement making—also produced aerosols, which are tiny particles that linger in the atmosphere for weeks and reflect heat from the Sun.

Previous studies have suggested that if a lot of these industrial processes were to suddenly shut down, it would lead to short-term warming because the atmosphere would lose the reflective effect of aerosols. But as the lockdown cleared skies, temperatures didn’t rocket.

In new research, we show that lockdown had a negligible effect on global temperatures. So what really happened?

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