The possibility of legal action taken by parties injured as a result of climate change has been thrown around endlessly in environmental circles. In the end, the problem is always the same: on whom, or on which entity, does responsibility for damage fall, and to what extent?

Last week the US supreme court heard opening arguments in Massachusetts vs EPA. The petitioners – including a dozen US states, the American Samoan government and other interested parties – are taking to task the US federal environmental regulator’s 2003 decision that greenhouse gas emissions from new vehicles are not within its statutory authority to regulate.

But the Clean Air Act lays out that the EPA administrator ‘shall by regulation prescribe’ standards for emissions from motor vehicles that ‘cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.’

The case is widely seen as an end-run by the states around the federal government’s refusal to consider mandatory abatement measures. It seems likely to stand or fall not on the question of the EPA’s regulatory responsibilities, but on whether the plaintiffs have legal standing to bring the case before the court. They need to demonstrate specific harms that would be accrued as a result of the EPA’s actions.

That’s tricky. There are two questions: first, can specific, damaging events reasonably be tied to human-induced climate change, and; second, can the proportion of total global emissions over which the respondent has control (in this case around 6%) be reasonably expected to significantly impact on such events?

On the first question, scientific uncertainty comes into play – how does it match up against the court’s required evidentiary standard (or, for that matter, the political persuasions of the justices)? Some potential impacts – changing hurricane frequencies, for example – remain highly uncertain, while others, like sea level rise, are at least qualitatively less equivocal.  

The second question – and indeed climate change more generally – illustrates Harden’s ‘tragedy of the commons’ conundrum in a nutshell. Avoiding this situation is the whole point of regulation, and yet the EPA’s lawyers mobilised the old ‘little fish in a big ocean’ argument to attack the standing of the states during opening (see here).

This may have a certain isolated logic to it, but in the broader context it’s absurd. That the area of contention is one small sector of the world’s total emissions shouldn’t excuse it from regulation – the logical extension of such an argument would be to arbitrarily cut up all areas of responsibility into smaller sectors and declare each ‘insignificant’ simply because the impact of each can no longer be quantified.

The case is really a test of whether the law as written is capable of enforcing a broader moral principle that many of us quite intuitively grasp, and that is increasingly coming to the fore as the planet strains with the load of 250 years of industrialisation and the globalisation of its impacts – the fact that our actions only have a measurable impact in aggregate makes each of us no less morally accountable for them. Per capita emissions are the rightful measure of our accountability, and the US, along with Australia, is one of the worst on this basis.

If the technical letter of US law renders it impotent to deploy the federal regulator in defence of this principle, then this probably says more about legal anachronism in our brave new world than it does about the merits of the case.