He lobbied for withdrawal I belive - but again I really wouldn't read into that a huge amount, I know plenty of environmentalists who were supportive of the US withdrawal simply because it is a largely symbolic agreement that arguably does more harm than good (I'm not saying I neccessairly agree but the argument does have some merit).
It frustrates a lot of market environemtnalists (not saying Paul is one, but his rhetoric over the PCA is similar to theirs) because it seems to prioritize negative action over trying to grow the economy and protect the environemnt in symbiosis - you can see why a lot of republicans especially would be in opposition to it, and why Paul's relationship with the environemntal debate gets quite radical when it comes at the expense of the livelihoods of the most vulnerable in the short term. It almost seems like he's been pushed further into the "kick the can down the road camp" as a result of being called a climate denier when he tries to protect jobs - it gets very cyclical.
It doesn't help the environmental debate to label anyone critical of the Paris agreement, XR, Greta etc as just "climate deniers" (seems to happen a lot) as the market environementalist argument seems to evoke for some reason.
Personally, market environmentalism and the work of the
British Conservation Alliance and the
American Conservation Coalition have always been more attractive to me than most of the policies we've seen in recent years, but that's just personal prefrence.