Although science and the law both deal with evidence and uncertainty, they approach these issues in ways that are different enough that a courtroom is generally a lousy place for determining the status of a scientific field. Nevertheless, so many aspects of our society now have a foundation in the sciences—medical care, policy, education, etc.—that science inevitably bumps up against the law quite often. One of the more striking instances of this occurred last week, as an Appeals Court handed down a ruling on greenhouse gasses that was largely overlooked because it happened to come down in the same week that the Supreme Court tackled health care law.

The decision is long on legal details, but there are some important lessons about science and its role in formulating policy that are worth drawing out.

Failing on legal grounds

We'll get the legal background out of the way first. The case is the latest in a long line of decisions about whether the Clean Air Act (CAA) requires that the EPA regulate greenhouse gas emissions. Back in the Clinton administration, several states banded together to sue the EPA, arguing that the CAA required that it take action. By the time the case had made it to the Supreme Court, the Bush administration's EPA was arguing (I'm obviously simplifying here) that greenhouse gas emissions were just too complicated to be regulated.

On 5-4 lines, the Supremes determined that the CAA was unambiguous: the EPA had to determine whether greenhouse gasses qualified as a pollutant and, if so, it needed to suck it up and figure out how to regulate them. Although the Bush-era EPA never got around to following the court's instructions, the Agency has since made an official endangerment finding and announced a preliminary set of rules to govern greenhouse gas emissions from large sources.

A different set of states, combined with a variety of industry groups, have sued to overturn the endangerment findings and block the regulations. The Appeals Court for the District of Columbia Circuit has now rejected that attempt.

From a legal perspective, the rejection doesn't appear to be especially interesting. Ironically, the states and industry groups made arguments extremely similar to those put forward by the Bush-era EPA when it was trying to shirk its legal requirements on greenhouse gasses. Since those had already failed at the level of the Supreme Court, the Appeals Court also found them unpersuasive. Although there is some amusement value in seeing the states get slammed for hypocrisy when claiming they, rather than the EPA, should be doing the regulating: "Essentially, State Petitioners’ reply brief contends that, contrary to the position taken in the opening brief, they want more regulation, not less, and that they wanted regulation sooner rather than later."

The law as a sanity check

The more interesting parts of the decision comes when it turns to science. As a former scientist now deeply enmeshed in the scientific process, it's usually easy to see which arguments have scientific merit. But it's also easy to see that the public often doesn't see things the same way as a scientist does. For example, a lot of people outside the scientific community seemed to think Intelligent Design was scientific in nature and had some merit—it took its legal dismemberment at the Dover Trial for the idea to lose steam with the public. In that sense, the legal realm can provide an important outside perspective on where the science stands.

(This doesn't always work brilliantly, of course. For one example, see Antonin Scalia's dissent in the case that declared teaching creationism an unconstitutional imposition of religion [joined by Rehnquist]. As far as Scalia's concerned, you don't need to actually weigh evidence—if a few guys with PhDs say something's science, that's good enough for him. Fortunately, seven other justices had somewhat higher intellectual standards.)

Climate science seems to be another area where an outside sanity check would be a good thing. From my perspective, things were very straightforward: temperatures have gone up, the greenhouse effect and ocean acidification clearly exist, and the various attacks on the field and researchers themselves were generally overblown nitpicking. But it's clear that a lot of people haven't seen things that way, and some outside perspective could go a long way towards helping me feel I wasn't just convincing myself.

The Appeals Court delivered that, and then some.

One of the areas where a lot of people stumble when it comes to climate science is that they can't separate the science from its policy implications. By design or chance, it turns out the CAA explicitly separates them—the EPA is required to perform its endangerment evaluation based on the science, ignoring any policy consequences that might be dictated by the results. "Policy judgments," the court ruled, "have nothing to do with whether greenhouse gas emissions contribute to climate change. Still less do they amount to a reasoned justification for declining to form a scientific judgment."

So, how does one form a scientific judgement? Ideally, you consult with the people who have the most relevant expertise in the area, and determine what the current state of the field is. So, the EPA considered reports on climate change from groups like the IPCC and the National Academies of Science. That, apparently, didn't sit well with the states and industry. "State and Industry Petitioners assert that EPA improperly 'delegated' its judgment to the IPCC, USGCRP, and NRC."

This is in keeping with the general disparagement of expertise when it comes to arguments over climate change, where many arm-chair scientists feel they've stumbled across insights that people who have devoted their lives to the topic have somehow missed. The court would have none of it, stating "This argument is little more than a semantic trick."

EPA simply did here what it and other decision-makers often must do to make a science-based judgment: it sought out and reviewed existing scientific evidence to determine whether a particular finding was warranted. It makes no difference that much of the scientific evidence in large part consisted of 'syntheses' of individual studies and research.

Expecting it to do otherwise, the decision notes, would have some ludicrous consequences. "This is how science works. EPA is not required to re-prove the existence of the atom every time it approaches a scientific question."

The IPCC in particular has been the target of criticism, with accusations of a selective use of the literature and the fact that a few errors made their way past its review system. But the Court puts that in perspective, noting that the latest IPCC report references 18,000 peer-reviewed papers. And, as far as the judges could tell, it did a good job with that information. "State Petitioners have not, as they assert, uncovered a 'pattern' of flawed science. Only two of the errors they point out seem to be errors at all, and EPA relied on neither in making the Endangerment Finding."

The climate e-mails stolen from the University of East Anglia also made an appearance in the suit, being used to cast doubt on the quality of the underlying science. Again, the Court was unpersuaded, finding "The petitioners’ claims based on the CRU documents were exaggerated, contradicted by other evidence, and not a material or reliable basis for questioning the credibility of the body of science at issue."

Like all other fields of science, there are clear areas of residual uncertainty when it comes to the climate (many of them, in fact, are discussed in the IPCC reports). To many of the critics of the field, however, the uncertainties are so large that it's impossible to say anything with much confidence. But those arguments tend to lose sight of the number of things that we do know with a high degree of confidence. "To avoid regulating emissions of greenhouse gases, EPA would need to show 'scientific uncertainty... so profound that it precludes EPA from making a reasoned judgment as to whether greenhouse gases contribute to global warming,'" the Court concluded. The remaining uncertainties simply don't rise to that level.

The law separated from the science

Legal experts should never have the last word on climate science—they're not the experts in this area, and courtroom proceedings aren't structured in a way that will necessarily bring out the best scientific information. But in this case turned out to be less about the science, and more about the public arguments over the science.

Ultimately, the states and industry turned their case into a neat package that brought together most of the arguments you'll see if you follow the public debate. While scientists may argue over the relative strengths of some specific feedbacks, the questions the public sees (reiterated by the states) blur the lines between the science and our policy responses to it, while focusing on things like whether the IPCC can be trusted and if the stolen University of East Anglia e-mails are an indication of scientific fraud.

The language of the CAA compelled the court to examine the science separately from the policy issues. And, when it came to the science, the court didn't have to focus on the details—it just had to determine whether the EPA managed to base its decisions on a reasonable overview of our current state of knowledge on greenhouse gas emissions.

And, rather decisively, the court ruled that it had. The stolen e-mails and attacks on the IPCC's credibility, in the court's view, were little more than a distraction from the EPA's attempts to identify the groups with relevant expertise, and to summarize what they (and their 18,000 references) have concluded. In short, the popular arguments largely occupy a completely separate sphere from the relevant science.

It's an important message, one that applies to a number of other fields. It's a bit of a shame that the health care decision completely overshadowed it.