If the USA falls into a debt crisis the result will be global economic disruption.
If the world falls into runaway climate change the result will be the extinction of the human race and possibly all life on earth.
Personally I'm more comfortable with the possibility of the first than of the second.
If we could have runaway climate change somehow not disrupt global economy, we could eventually tech our way out of it. But the game over point is when the economy stops, and humanity no longer has capability to slow down and mitigate the effects of warming. At that point there isn't much left of humanity anyway.
E.g. how easy would it be for us to bootstrap back to space capabilities after a catastrophic war wiped out a large portion of world economic capability?
If something pulled the plug on our economy, all the technology we have today would disappear in few years to decades. Devices wearing out with no way of repairing them or producing new ones. We'd regress to medieval times, because that would be the most advanced things available energy sources would support.
The industrial revolution happened because we had easy access to high-density energy source in the form of coal. Maybe, given enough time, some survivors would figure out how to do a new industrial revolution without it, though I'm not having high hopes. So whatever is left of humanity would have to wait until the Earth recycles enough living matter to create new deposits of high-energy something.