Without wanting to get pedantic, the Paris Treaty was not ratified by the US.  To be ratified under the US system, a treaty must be approved by the US senate.  Obama noted that the previous climate change treaty (Kyoto) was defeated unanimously (98-0) by the senate and Paris would also certainly be defeated so he brought it in by subterfuge.  He made the ridiculous claim Paris was not really a treaty and so he could bring it into force by executive order rather than senate approval.  BO gave off a redolent odour in doing this as he did with several other executive orders.  Your mileage may vary.

Trump has not actively or otherwise engaged in climate change denial for the very good reason that everyone knows the climate has been changing forever.

He simply refuses to play patsy to those who want the US to throw hundreds of billions of bucks at 3rd world dictators who will only pretend to tackle this problem.

Meanwhile, the US will continue to achieve real results in FFE reduction.