Logically, killing humans would be way down on the list of potential Global Warming solutions. We would have to exhaust all other methods first. Just banning private vehicles would save a few billion from extermination. Green energy tech and Nuclear power would save more. Vegetarian diets even more. Reducing organic waste, involuntary birth control, carbon sequestration - it’s a long list of better incremental solutions. They may be more costly than extermination, but they’re infinitely more ethical. It’s only logical if that’s the sole solution that ensures some of the population survives. We’re a long way from that condition.