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2020 is predicted to be an unusually warm year and we are already seeing a lot of unusual temperatures. I was wondering, how much of an impact the reduction of aerosol emission from the global lockdown had on this. I am not a climate scientist, but as far as I understand it: Aerosols are a short lived byproduct of our industries which increases atmospheric reflectivity. Because of this less sunlight reaches the surface of the earth -> less warmth is created in the first place. Because they are so short-lived shutting down industries should result in an almost immediate reduction in atmospheric reflectivity -> more sunlight reaches the earth's surface -> more warmth is created. That sounds like it makes sense in theory, but does it in praxis?

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Depending on type and size of aerosol there can be scattering, (Mie- and Rayleigh- scattering), atmospheric windows filter radiation, we have absorption, transmission and transformation of wavelengths which all influence the amount of energy that's trapped or reflected back.

The lockdown has led to a significant reduction of aerosols and drastic improvement of air quality in some regions (meaning not everywhere), but reliable studies seem to be rare atm. Evaluation is underway, but i think we must wait until a season has passed and activity has returned. A huge effect on temperature has afaik not yet been observed and described and if, it was towards a local decrease in temperature, not an increase. Anyway, the positive effects of lower economic activity are ceasing as no or little attempts are being made to use the reset for a transition to more sustainability.

Two examples I found, so far:

South-East Asia from satellite observation https://www.sciencedirect.com/science/article/pii/S0048969720331788

... enforced lockdown at different degrees to contain the spread of the disease, which has brought some positive effects on natural environment.

Morocco, a slight (-0.3°C) reduction in temperaure, but higher variablity https://www.sciencedirect.com/science/article/pii/S0048969720330588

... not much for day temperatures for beyond 40°C in the area.

... the emissions from vehicle exhaust and industrial production were significantly reduced, which contribute to the decrease in the concentrations of the studied pollutants ... local emission reductions related to the lockdown were overwhelmed by the contribution of long-range transported aerosols outside areas.

tl, dr: No, probably not, it may locally temporarily lower the temperature by a tiny bit, but overall this effect seems to be shadowed. But future work will show, it is too early to be definitive because the story still develops.

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