So, most of the US's recent reductions in CO2 emissions are due to fracking, which has produced enough natural gas at a low enough price to outperform coal, leading utility managers to shutter coal plants.
I don't see why this won't continue, Paris Agreement or not -- it's pure economics. I estimated here that 70% of recent US CO2 reductions are due to fracking -- that is, not down to a deliberate shift to renewable energy sources or increases in energy efficiency, but simply due to getting the same amount X of energy from natural gas instead of coal.
This shift can't go on forever. I estimated here that at best this can lead to a US per capita CO2 emissions about 15 metric tons (t) CO2/yr. That's still huge, relative to the world, whose per capita emissions are about 5 t CO2/yr.
Obama got lucky with fracking. It grew during the end of the GW Bush administration, and progressed strongly throughout Obama's two terms. The US committed to a 26-28% reduction in 2005 CO2 emissions by 2025. Fracking has actually put us on that trendline:
Trump can try to affect the 30% of US CO2 reductions that come from nonfracking sources -- better gas mileage, more electric cars, some utilities' shifts towards wind and solar, and what else? -- but I don't really see how he will delay the transition of utility power sources from coal to natural gas. That will remain as long as natural gas is the cheaper source.
And is Trump really going to expect car manufacturers to build cars that get less gas mileage? No -- they're not just designing and building for the US, but for Europe too, and Asia. And to consumers who can afford new cars, who are more smart and level-headed.
It seems to me that at best Trump can delay some CO2 reductions -- though only a fraction of what the US emits. The other reductions are happening because it's finally economical for them to happen.
And because major US states want them to happen, because they see and understand the future in a way that completely eludes Trump.
So I think Trump's decision on the Paris Agreement -- probably based more on his psychological weaknesses, of needing to always play the victim, to think that everyone, everywhere is against him, which he clearly projects onto America -- might not be as bad as is currently feared. But in no way because of him.