there's a dilema - what's worse: mankind destroying itself by a war, or overpopulating and polluting? Well, it's what the wars are good for. Human killing sounds brutal, but... I don't know. Population growth is fastest in areas with the most amount of people...
We caused these things. I suppose most of the people are meat-eaters. They can convert to vegetarians, btw. But we pollute oceans, we destroy rainforests. Less fish, less oxygen, more polluted air and water. Animals don't have space to live, humans and microorganisms may be sensitive to global warming, the plants are dying, so vegetarians have nothing to eat. Meat-eaters as well, because animals die too.. Everything will be poisoned and probably 12 milliards of people in 2040. D'oh.