Cougar is right about over population.
The problem is the only way to mitigate climate change and over population is for humanity to make incredible sacrifices. I am afraid to say I don’t think democracy can bring that about. It is a problem that requires everyone to undertake the same sacrifices. People are not stupid, but we mostly lack the knowledge to make the choices. We are scientifically illiterate. We lack faith in science. Democracy gives everyone who doesn’t know, the power over people who do know.
when I was born, we had a form of one world government. The sun never set on the British Empire, but it was unsustainable. The best way to overcome this, if we can, is a global overhaul of education. No one should leave school without a thorough grounding in mathematics, chemistry, physics biology and geography. It will be a massive investment and time is critical. A scientifically literate population tends to have fewer children and is better able to make informed decisions.