When we say that the United States is joining Syria and Nicaragua by not participating in the Paris agreement, I think it’s not fair to leave it at that, because neither of them refused to sign for reasons anything like the selfish ones of the United States.
Syria was under sanctions making it complicated to even attend, and on top of that were embroiled in intense civil warfare and not in a great position to make a commitment like that. They didn't disagree with it, but were never involved with the deal in the first place.
Nicaragua actually felt that the Paris agreement was not strict enough, arguing that they didn’t want to be complicit in a voluntary effort that didn’t properly allocate the responsibility to large countries for being the ones who poisoned the environment in the first place, nor impose a punishment on anyone failing to comply with the standards. Nicaragua is one of the countries that’s most affected by climate change but least responsible, and they felt that wasn’t fairly reflected in the accord.
The United States is the ONLY country that has rejected the Paris accord because of the belief that our environment is less important than our profit. Even oppressive regimes and the poorest nations in the world are smarter than that, or at least know when to keep their mouths shut and play along. The USA is not really in the league of Syria or Nicaragua, but alone in the refusal to cooperate out of pure greed.