Actually, Obama signed the treaty and was too lazy to get Congressional approval. But even if he did, the accord is still non-binding agreement which is why most of the nations of the world signed it. There is no enforcement and each nation do what they want...or don't want. Now if this was an totally binding agreement, many nations such as EU, China, India, Japan or any other industrial powers probably will not sign it. And it would requires Congressional approval to make it legal in the US. As a non-binding treaty, its just a PR stunt, Trump should have left it alone.