A few days ago, I got mail from a colleague at Climate Action Network International, a communications guy, asking for a comment on the US National Academy of Science’s recent climate reports, or rather on the US emissions budget that is recommended / affirmed in these reports.   It turned out to be quite an interesting request.

First, though, I gotta say these reports only strengthen the scientific case.  For example, the IPCC’s 2007 Forth Assessment Report says that sea levels could rise by between 0.6 and 1.9 feet by 2100, but recent studies have suggested that this is far too optimistic.  The NAS reports incorporate this newer research and concludes that sea levels could rise by as much as 6.5 feet in during this century.

Second – and this is the point – I was a bit surprised by the way the NAS approached the problem of calculating the US emissions budget.  The standard methodology in the climate world is to estimate a remaining global budget (which is hard) and then to work out the “share” of this budget that properly belongs to each country (which is harder).  And you have to admit this approach makes sense; after all, when the US – or any country – “takes” a budget, less is left for everyone else; which is why climate, fundamentally, is a sharing problem.  Anyway, I expected to find some version of this approach in the NAS reports.  How else could they calculate a recommended US budget?

The NAS authors, however, manage to sort of use the budget approach without actually spelling out the global budgets that they are leveraging in their analysis, or saying anything about how these should be shared.  Rather, they approach both global and national budgets indirectly, by way of a recent study by the highly-respected Stanford Energy Modeling Forum, that at the end of the day simply aggregates “bottom up” estimates of what the US and other countries can reasonably (e.g. cost effectively) be expected to do.

The method is simple.  The studies calculate the US emissions budgets implied by domestic emissions cuts of 50% and 80% below 1990 emissions levels, cuts that yield 2012 – 2050 cumulative budgets of 203Gt CO2-equivalent and 167Gt CO2-equivalent respectively.  These numbers (compare them to 266Gt, which would result from a continuation of the 2US’s 2008 emissions level) are then correlated to global studies, such that the authors can say (page 28), apropos their most stringent case (450 ppm CO2-equivalent) that …

“atmospheric GHG concentrations can only be kept below 450 ppm CO2-eq if the United States and other high-income countries, along with China, India, and many other low- and middle-income countries around the world, take aggressive actions to reduce emissions staring within the next few years.”

In other words, NAS commends a 2012-2015 US budget of 203Gt-167Gt CO2-equivalent as “reasonable,” but this budget is never discussed, or justified, with respect to the global budget.

Which means that the NAS is able to note that it is reasonably consistent with emerging US policy, and with an ambitious global target, without once discussing why they have reached this conclusion, or what it implies about global budget sharing, or indeed about why the budget that remains to be shared is so damn limited.  It’s as if bottom-up national budgets made some sort of scientific sense.  As is, more particularly, they could calculated without raising sticky question like historical responsibility and burden sharing.

Why would this approach strike the good folks as NAS as reasonable?   Because today’s overarching climate policy problem is widely seen as finding the best way to rapidly build momentum towards global decarbonization.  And because this is widely taken to imply not talking, or at least not talking loudly, about how serious the climate problem really is, and concentrating, instead, on “getting started.”

In this sense, the NAS approach is consistent with the “pledge and review” approach that the US is pushing in the international negotiations, an approach in which countries offer up the policies and measures that they can contrive or justify domestically, and we’re left, after the fact, to work out what these pledges add up to.  And to hope for sunnier negotiations ahead.

Not surprisingly, this method supports both the thrust of the science and the thrust of US policy.  The question, though, is if the proposed US emissions budget is fair, and if it would be seen as fair, and if by being seen as fair it would be conducive be to the sort of international accord that we actually need, one that has a “high probability” (in IPCC’s lingo) of actually avoiding dangerous climate change.  Here, the only thing that the reports can say is that their recommended US emissions budgets would be 450 CO2-eq consistent if all the major emitters take aggressive action in the short term.

Bottom line: it’s a pragmatic methodology, but it’s also a strange one.  Science for strange days.

The good news is the recommended numbers explicitly exclude international offsets!  See page 29: “Note that these goals are presented as limits for cumulative US domestic emissions (rather than through international offsets.”  The bad news, and it’s unfortunately the flip side of the good news, is that the recommended domestic action is taken as the sum of US obligated action.

This is a key point. The problem is that, from an international perspective, it’s not the size of US domestic effort that is, finally, the issue.  It’s rather the size of the US’s combined domesti
c and international effort.   But in the NAS terms, there is no international effort.  Or rather, there might be, but it’s not really mentioned.  The only relevant discussion (that I could find) is a discussion of how international offsets would result in international transfers (on top of domestic reductions), but if and only if (the report is clear here) there’s no “double counting.”

The only point at which the author’s make an explicit comparison to a fair-shares global framework proposal is on page 31, where it is noted that, according to the German Advisory Council on Global Change, an equal per-capita approach allocates the US a budget of 35 CO2-eq over the same 2012-2050 period.  Obviously, this is a much smaller US budget than the one the National Academies recommend, but the issues here are not discussed.

In sum, the NAS analysis is odd and opaque, and when it refers to the sort of global emergency emission reduction trajectory that we actually need (450 CO2-equivalent isn’t a bad marker, though it’s still a lot more than 350 ppm, as in www.350.org) it repeatedly states that current US policy is plausible consistent with that trajectory (a weak claim) only if it is accompanied by “immediate, aggressive, and comprehensive global GHG emissions reduction efforts.”  But would they be?  It’s unlikely, not unless US domestic reductions dropped to the very lowest end of the recommended range – without international offsets! – and if this drop was accompanied by a very significant commitment to international mitigation and adaptation, a commitment that the NAS takes as being outside its proper purview.

Other than this, though, it’s a good report!