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The lockdown imposed in China and other countries in response to the COVID 19 pandemic has resulted in a dramatic change in air quality. Factories and transport systems have shut or continue at greatly reduced capacity, so that emissions of many atmospheric pollutants are greatly reduced.

Studies of climate change have shown that atmospheric pollutants emitted by human activities contribute to anomalous cloud conditions which result in a net negative radiative forcing. Results from IPCC 2013 (see also the wikipedia page for the key IPCC results) gives an estimate of -0.82 W m-2, which offsets the positive contributions estimated at 3.18 W m-2, leading to a net forcing (in 2011) of 2.29 W m-2 (with substantial uncertainty on all terms). Removing the negative effects of the short-lived atmospheric pollutants would, based on these 2011 results, give a 39% increase in radiative forcing (as a best estimate -- with large uncertainties).

The questions: (1) have we, in the last few months, seen an increase in net anthropogenic radiative forcing of close to 40%? and (2) what are or could be the consequences of such a change both in the short term?

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    $\begingroup$ Interesting question. It probably is too early for a well founded answer. Weather conditions may have negated some of the positive effects. sciencedirect.com/science/article/pii/S092134492030135X. $\endgroup$ – user20217 Apr 23 '20 at 10:41
  • $\begingroup$ Thanks, that is a very interesting and relevant article. It suggests that the reduction in emissions is less than I was expecting, maybe only 20% of the pre-covid levels. However, it only covers the period Jan 1st to Feb 12th, so there may have been greater changes since then. $\endgroup$ – M Juckes Apr 23 '20 at 11:07

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