Global Warming or Green House Gas Driven Global Warming?
From what I read, Green House Gas Driven Global Warming has an increase in stratospheric temperature signal, while the absence of it just means that Green House Gas Driven Global Warming isn’t the primary driver.
You can still have global warming, but the signal of the green house gases is missing.
I believe their claim is essentially correct, but that they exaggerate the amount of stratospheric cooling due to CO2. Currently we see a lot of stratospheric cooling (about 0.5 degrees per decade), but a lot of that is natural and due to the sun putting out less ultraviolet. IOW the "signal" that they are pointing out is not the "signal" from CO2 global warming, but a natural effect of the deep solar minimum.