I have a great idea, what if you added an animal function where it has the population of the animals and how muck co2 they produce and the population can increase/decrease depending on the oxygen to co2 ratio.
Better yet: the ability to enact a reproduction limit on humans à la China's only-two legislation and the U.S.'s 1960's only-two fad. The game's meat ban and the Sanctuary option does plenty as far as manipulation of nonhuman species, which is apropos because humans are the root of global warming, not nonhuman animals. We know now that animal agriculture is responsible for more greenhouse gases than the entire global transportation industry, and the most important thing we could do as far as immediate benefit to the amelioration of global warming would be to stop eating all animals, their breastmilk, and calcified periods. With this in mind, it would actually be more accurate (albeit complicated) to introduce methane to the game, and/or a greater decrease in CO2 levels with the enactment of the meat ban.