What the government should do about climate change should be decided by legislation agreed upon by the President and Congress, not by an administrative agency.
That could employ subject matter experts and scientists to draft reasonable and prudent regulations, hopefully away from the influence of lobbyists? What a novel concept.
Or they could legislate. What's the purpose of electing lawmakers if they just hire random bureaucrats. If they want advice they have the money to get that advice
It is common and reasonable for legislation to delegate responsibility. Administrative rulemaking has been around for a long time and will continue to exist.