The Phys.org article CO2 dip may have helped dinosaurs walk from South America to Greenland quotes Dennis Kent, "adjunct research scientist at Columbia University's Lamont-Doherty Earth Observatory" in the following:
On Earth, areas around the equator are hot and humid, while adjacent areas in low latitudes tend to be very dry. Kent and Clemmensen say that on a planet supercharged with CO2, the differences between those climatic belts may have been extreme—perhaps too extreme for the sauropodomorph dinosaurs to cross.
"We know that with higher CO2, the dry gets drier and the wet gets wetter," said Kent. 230 million years ago, the high CO2 conditions could have made the arid belts too dry to support the movements of large herbivores that need to eat a lot of vegetation to survive. The tropics, too, may have been locked into rainy, monsoon-like conditions that may not have been ideal for sauropodomorphs. There is little evidence they ventured forth from the temperate, mid-latitude habitats they were adapted to in Argentina and Brazil.
The article references Dennis V. Kent el al., "Northward dispersal of dinosaurs from Gondwana to Greenland at the mid-Norian (215–212 Ma, Late Triassic) dip in atmospheric pCO2," PNAS (2021). https://www.pnas.org/cgi/doi/10.1073/pnas.2020778118
but currently the link to the article is not working; perhaps it's not actually been published yet.
Question: Why is it that "With higher CO2, the dry gets drier and the wet gets wetter"? Does this adage come from modeling, from data, or from both? Is it a well-accepted rule of thumb?