OH MYYYY. That is a good analogy. The one thing that could really help is a safer revival of nuclear power. I think humanity has to reassess the costs and benefits and redeploy where safe. Yes, Chernobyl was awful, but the Soviets were derps all the way around. Yes, Fukushima Daiichi Nuclear Power Plant disaster was awful, but it was situated in such a poor place.
Nuclear power is a good idea. It’s an efficient power source and despite highly toxic can be managed
That said fossil fuels have ensured that fewer people have died from natural disasters. Plastics also ensure clean medical facilities and plastic is made from petroleum. Melting seas would lead to a runaway greenhouse effect that would wipe out all life in Earth. CO2 could raise temperatures another 0.5C but methane and water vapor could increase it another 10C potentially which could definitely lead to mass extinctions. Even 1-2C can lead to extinctions of sensitive species which can effect the species that eat those species. Of course, there are some species who will be less predated so there will be more of an abundance of those species
That said, I don’t endorse the marching desert hypothesis or that six degrees will destroy the planet. Six degrees aka 21C would likely create lush rainforests throughout the globe and crocodiles would likely exist in Alaska, Siberia, and Greenland