SCOTUS said the EPA may regulate, not that they must regulate.
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Under the doctrine of “Chevron Deference,” the Courts must defer to the administrative agency’s decision on how policy is implemented if that policy is a reasonable reading of the statute directing their policy. So long as the agency jumps through the Notice and Comment hoops and other rules regarding rulemaking, the agency can do what it wants without judicial review.
The case of Massachusetts v. EPA was a case where the Court did order the EPA to regulate CO2, but it was pretty much an aberration from Chevron Deference. The decision has been heavily criticized, even by the left who loved it when it came out. The decision was used against the left in the 5th Circuit case of U.S. v. Texas, the DAPA decision, as it justified giving Texas standing to sue the Federal government over immigration policy. Having seen their monster turned against them, the left might not be so willing to use Massachusetts v. EPA as precedent.
So my take is that if the proper rulemaking procedures are followed, the SCOTUS will defer to the agency in regard to “greenhouse gas” emissions. If they don’t, they will have to throw out the whole basis of the administrative state. You might like that, but the alternative is the administrative state run by judicial fiat instead of executive direction, and we should not favor that.