In the immediate aftermath of the 9/11 attacks, aircraft were grounded for several days. This resulted in several days when there were no jet contrails crisscrossing the skies above the United States. As a result, climate scientists were able to review the data for cloud formation for the days that aircraft were grounded and try to assess how much impact jet travel had on the formation of cirrus clouds. Early papers found a strong increase in daytime temperatures, although more recent studies have raised questions about the early results.
In a similar way, the near global shutdown of industrialized economies will provide climate scientists a way to test their models and learn how the Earth’s climate system responds. For example, China’s air has become much cleaner as a result of the COVID19 pandemic. Less industry means lower emissions of particles (aerosols), and fewer people traveling from place to place reduces the amount of nitrogen oxides, contrails, and aerosols. Less carbon dioxide (CO2) too, of course.
Given the short-term changes in industrial output, I’m guessing we’ll see some fascinating atmospheric science come out of this. It’s a thin silver lining to a horrible situation, to be sure, but scientists are good at using every kind of change, good and bad, into meaningful, useful data.
So this is my hypothesis. I hypothesize that we’re going to see an increase in global surface temperature as a result of the COVID19-driven economic depression. This is because the dramatic decrease in aerosols (which tend to cool surface temperatures), reduction in contrail-driven cirrus clouds, will be more important than the drop in CO2 and nitrous oxide over the time scale of the next few months. Since we’ll have cleaner air and fewer high-altitude clouds, the effect of CO2 will be more pronounced and the global surface temperature will increase.
Furthermore, I hypothesize that we’ll see surface temperature start to drop in those places that restart their industries first because of the effects of aerosol pollutants.
I look forward to finding out if my hypothesis is right.
Categories: Environment/Nature, Featured
Progressive Culture | Scholars & Rogues 
You’re going to be right. Forcing from CO2 is still positive (aka “warming in the pipeline” or “we haven’t caught up yet”). Forcing from aerosols will drop a lot – not sure if this is up to date, but a RealClimate article from 2007 says the typical aerosol particle only stays in the atmosphere for 10 days. The question is whether the reduction in human industrial activity will last long enough for the consequent warming to be detectable.