What the figure above shows, of course, is that there are fewer photons of IR reach space from the surface of the earth. This means that, in effect, the black body radiation, the brightness, decreases. That occurs at the positions in the spectrum related to each greenhouse gas.
The fewer the IR photons that make it out to space the hotter the globe gets.
That is what the writers of the Harries et al paper concluded.
Oh, and the brightness temperature was not absolute, that ∆ indicates change. The apparent brightness of the earth decreased because more IR photons are blocked from escaping to space.
What Lees wrote was amusing but irrelevant.
There is a clear exposition of the facts in the Harries et al paper here:
https://skepticalscience.com/empirical-evidence-for-co2-enhanced-greenhouse-effe...There are two GHGs more potent than CO2, methane (CH4) and nitrous oxide (N2O) and these gases are being released in bigger and bigger quantities as the frozen tundra at both poles melts. So much for a pause in the warming!