An IPCC scientist on twitter alerted me to this animation created by Chris Rentsch which analyses the data from the AIRS satellite measuring outgoing longwave radiation.
Here’s a still from the end of the video sequence.
As we can see, by 2019, there is a decrease in OLR at the wavelengths absorbed by CO2 (13-15um) as its atmospheric fraction increases. But we can also see that there is a much bigger increase in OLR at the wavelengths within the ‘atmospheric window’ (10-13um) where it isn’t absorbed by any atmospheric gases.
Chris correctly states that this is indicative of a warming, but refrains from drawing the rather obvious conclusion:
since the increase in OLR through the atmospheric window is much larger than the decrease in OLR due to extra CO2, the majority of the warming must be due to an external forcing (increased incident solar shortwave). Otherwise the surface would be cooling, not warming!
It turns out that according to the available data, this overall increase in OLR has been going on for a long time. Here’s the NCEP reanalysis.
The most likely source of the extra energy is the Sun, via a reduction in cloud cover, as measured by ISCCP.
There’s your ‘global warming’.
The further implication of this externally forced warming is that some proportion of the increase in atmospheric CO2 will be due to the Sun warmed ocean surface releasing it to the atmosphere and being less able to reabsorb it. What that proportion is remains to be determined, but the big reduction in human emissions due to the coronanpanic lockdowns have had no discernable effect on the airborne fraction of carbon dioxide.