It seems to me the only solution to this requires a unified global effort on the scale of how nations fought "total wars" in WWI and WWII - meaning it wasn't just the military fighting the wars, but most of the citizens back on "the home front" participating in the war effort and suffering and sacrificing as necessary.
We need individual, business, and government agreement and action. Just as Detroit stopped making cars and started making guns and tanks and airplanes in WWII, we'll need a huge industrial shift to solar power and wind power and whatever else it takes to stop the pollution and start fixing the environmental damage.
How about a draft or a job opportunity for eligible young men and women to work in programs similar to FDR's
Alphabet Agencies? These people could spend a year or two each cleaning up the oceans and rivers, planting trees in the rainforests and everywhere else, and all the other stuff that I'm not knowledgeable enough to list, in exchange for college tuition and/or other benefits once they've served their time.
Huge changes to modern life will be required, such as severely limiting the use of gas and diesel engines in automobiles, airplanes, and eliminating their use entirely for non-essential things like auto racing (sorry, guys), power-boating, lawn-mowing, and so forth. I don't know much about the specifics of industrial pollution, but obviously that must be highly reduced as well.
It will also require some strong enforcement of these new and radical policies by more powerful nations or alliances thereof in places that choose to ignore them, such as in countries where rain forests are being destroyed and species are being wiped out.
There are probably a
hundred thousand other things like these that I don't know enough about to mention.
What would humans do if threatened by alien invaders or an approaching asteroid? We need that kind of action, starting today.
Otherwise, we might as well just start partying, à la
On The Beach.