We went through something like this in the gun threads.
The belief that although nobody could come up with a working solution, there had to be one out there.
Liberalism relies extensively on the belief that there is no problem in human existence that can't be solved by strong political leaders taking strong political action.
This has not worked well in historical practice, but that's another story.
We can simplify the question by narrowing the field of view to just China, which now accounts for something like 30 percent of total CO2 emissions and is approaching double the U.S. output. Granted, China's per-capita output is lower, but the AGW premise is that the environment counts total molecules, not how many people generated them.
Start with China, and we'll go on from there.