Judicial deference to administrative agencies?

I bet the FDA wishes it got the kind of deference on offer in the D.C. Circuit opinion upholding the EPA’s greenhouse gas regs:

As we have stated before in reviewing the science-based decisions of agencies such as EPA, “[a]lthough we perform a searching and careful inquiry into the facts underlying the agency’s decisions, we will presume the validity of agency action as long as a rational basis for it is presented.” Am. Farm Bureau Fed’n v. EPA, 559 F.3d 512, 519 (D.C. Cir. 2009) (internal quotation marks omitted). In so doing, “we give an extreme degree of deference to the agency when it is evaluating scientific data within its technical expertise.” 

…If a statute is “precautionary in nature” and “designed to protect the public health,” and the relevant evidence is “difficult to come by, uncertain, or conflicting because it is on the frontiers of scientific knowledge,” EPA need not provide “rigorous step-by-step proof of cause and effect” to support an endangerment finding. Ethyl Corp. v. EPA, 541 F.2d 1, 28 (D.C. Cir. 1976). As we have stated before, “Awaiting certainty will often allow for only reactive, not preventive, regulation.”

(Compare Alliance for Natural Health v. Sebelius, which among other things finds that, because there was one well-conducted study supporting a health claim, the FDA couldn’t bar supplement makers from making the claim, even though four well-conducted studies didn’t support it.  See xkcd for the error.)