This kind of discourse simply frustrating. The assumption is that CDR and solar geo are being proposed as "solutions" - which they simply aren't, and shouldn't be discussed as such. The word "solution" should be struck from the record of climate discussions as a whole.
Just because any particular technology doesn't qualify as a "solution" doesn't mean R&D shouldn't be pursued. If an additional measure like solar geo, or DAC
could reduce climate risk, or (in the case of CDR) even
enhance mitigation for hard-to-abate sectors - then it's clearly worth at least thinking seriously about. It's particularly frustrating that Mann writes about these in the same context as "clean coal" and bridge fuels, which is a different kind of debate, and in the case of the former, universally recognized to be moot anyway.
I do wonder if the semantic confusion around the word "solution" merits further investigation. Hell, there's probably a paper or two waiting to be written just on the angst around the word "geoengineering" alone.