The DEC has figured out carry capacities for deer, turkey, black bear, squirrel, and other game populations for all of NY state. That info plus current population stats is how they determine how many hunting tags to issue each year to hunters. If they can do it with deer, then other can do it with humans. Earth's human carrying capacity should be maximized because humans are fricking awesome and there is good reason we are the dominant species. We are the best hope of all Earth's species to expand life to other celestial bodies. To do that we need maximum geniuses, and to do that we need as many smart people as possible having as many children as possible. The more geniuses born, the more we can figure out how to increase Earth's carrying capacity. I guarantee that if we aren't stupid an blow ourselves up, that HIGHER CO2 LEVELS will be needed at some distant future date in order to allow earth to host more humans comfortably, simply because higher temperatures and CO2 leads to more precipitation and faster crop growth, and food, fresh water, and air are the #1 things humans need to survive.