The President] shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur... The Constitution of the United States.
It really is that simple. Legalistic pretexts have arisen within the last generation, to avoid the complexities of actually conferring with people and convincing them you're right. Nevertheless, the "Paris Accords" are an agreement to which the Obama Administration was a signatory. The United States was not.
Maybe the PAs are stupid, evasive and a pretext for the waves of ever encroaching globalism that carries before it the banner of "Everything not obligatory is forbidden." Maybe they are sensibly-negotiated and scientifically defensible accords leading to a better future. I'm not Mark Ruffalo - I don't pretend to be a scientist. I read the conflicting experts and am very confused.
The treaty was never presented to the Senate, let alone approved by a 2/3rd vote. Consequently, if Mr. Obama wants to reduce his carbon footprint, that's his decision. The rest of us are no longer bound by the treaty he and his administration negotiated. That's the way this works.