The entire premise is based purely on association. Cause cannot be established, therefore any suggested solution cannot be expected to produce intended result. On the other hand, Allan Savory's experiments shows we can both produce more meat and more veggies for the same land use, and restore otherwise barren land.

On the third hand, we got data on the association between solar activity, cosmic rays, cloud cover and climate changes. It's currently controversial, there's still a debate going on about both whether it's real and if it is real its contribution to climate changes. The article appears to take the view that it isn't real, since there's no mention of it anywhere. It would likely weaken their case against meat. I mean, hey you gotta eat less meat, but we're not sure cuz of cosmic rays and stuff. The point here is that they cannot say anything for certain about meat and climate changes in the context of the current debate about cosmic rays. The two hypotheses are part of a larger hypothesis, but due to several unrelated interests - i.e. dogmas about diet and health for example - they are on opposite sides rather than forming a common front to explain a common, erm, threat.

On the final hand, plants thrive on more CO2. In fact, the same place we get the term "greenhouse effect", we also get the data that shows more CO2 causes plants to grow faster, bigger, taller. The technical term is carbon dioxide enrichment. If anything, if I was a veggy nut, I'd welcome an increase in CO2, therefore I'd welcome an increase in meat production and consumption just for that (if that were true to begin with, which it's not).