Until the war started in Ukraine global warming was on top of my list and still is so I have 2 issues in the #1 spot now. Can soon add N. Korea in there as well.
We are on the brink of environmental collapse with so many factors on the tipping point that once one goes down so do the rest like the house of cards we have built for ourselves.
The US can help without doing a thing if the super volcano in Yellowstone lets go as many believe it is preparing to do. It will cause temperatures all over the world to drop with resulting crop failures worldwide. The resulting famines will reduce the population drastically which will have the benefit of reducing CO2 output drastically. Sad that up to 100 million Americans could die from the initial blast and possibly a lot of Canadians too depending on which way the wind is blowing when the event happens but such is nature.
With temperature rise now estimated to reach 2.5 degrees by 2050 instead of the hoped for max of 1.5 it may take an event like a super volcano eruption somewhere in the world to turn this ship around before it ends up on the rocks.
I'm hoping it doesn't come to that. If WWIII starts we won't have to worry about any of his anymore.