Each car will likely get used less under him, and then eventually sold/gifted to others at a discounted rate. Those cars will most likely get used through their useful lifespan without any more or less effect on the world than they would have otherwise.
TLDR: If he buys a car a year, and drives the same number of miles as the average American, his total emissions are probably equal to someone who drives 28k miles a year.
Carbon emissions for a Model 3 vs a Toyota Corolla even out after 13'500 miles according to Argonne National Laboratory [1], which is slightly less than the average an American drives per year (14'263 miles [2]). Assuming that he drives as much as the average driver, his cars generate as much Co2 as a Model 3 (definitely not true for the Cybertruck, but he probably has low-build-emission ICE cars in the other 8 to lower the average), and he buys a car a year, he has roughly the equivalent emissions of someone who drives twice the average number of miles each year. For reference, a long haul driver (of which there are 300k-500k in the US [3]) drives 100-110k miles [4] a year (7-8x the average).
