Late last month the New York Times ran an interesting piece about the power of language and climate change. Central to the story is the concept of a carbon budget. On its face, the concept is simple. Drawing on complex models of the atmospheric and energy effects of carbon dioxide and other heat trapping gases, climate scientists have proposed a global carbon budget: the amount of carbon dioxide (or, we should add, the equivalent in other gases which can be far more potent) that can be emitted into the atmosphere without breaking the two degree Celsius mark. Turns out the numbers are not pleasant (like just about everything else with respect to climate change). In the latest IPCC report (the fifth, 2013), climate modelers estimate that humans have a total carbon budget of about 800 billion tons, of which humans have used about 530 billion tons, which means we only have 270 billion tons left. Given the average emissions rate of 10 billion tons a year, looks like humans and the rest of the planet have a little less than 30 years left, and that assumes that carbon emissions stay constant. If they grow, of course, the time shrinks.

While the numbers are sobering/depressing, if states and societies are really serious about avoiding more than two degrees Celsius of warming, these are exactly the hard numbers needed to provide concrete goals towards which to orient policy. So, the budget is all over the place in Paris, right? According to the Times piece, not so much. Turns out that policymakers in Paris are very concerned to avoid talking about carbon budgets because, if they do so, it has the potential to scuttle the whole process.

Why? Well I think there are some rationalist explanations. Numbers like a carbon budget would put non-compliance into stark relief, which in turn would make free-riding if not impossible at least very costly. But, I do not think this captures everything of what is going on here. Even when agreements and international commitments seem iron-clad, states have a way of getting out of them when they wish. Moreover, realist approaches to international relations do not put much stock in these kinds of consequences—the anarchical system allows and indeed can even incentivize agreement breaking, all in the name of sovereignty and self-preservation.

So why so much reluctance to use the carbon budget? I think some of it comes down to rhetorical entrapment—the idea that rhetorical claims are socially binding.  This functions in two ways. First, policy makers in most places have been saying climate change is a serious problem and we have to do something about it. They have rhetorically entrapped themselves in these narratives, which in turn gives much greater strength to policies undertaken in the name of climate change. Putting down hard numbers in this context would further the entrapment. Second, the concept of the carbon budget fits with the neoliberal normative narratives (carbon markets, cap-and-trade) that political leaders have used to talk about climate change. The concept of a budget fits right in with these economically-oriented discourses, and policy makers are so rhetorically entrapped within them that disavowing a carbon budget becomes impossible. There might be a third way: the idea of a carbon budget puts into simple numbers the problem of climate change and its relationship with human economic activity. Numbers seem to have a particular hold on the human imagination, so putting this relationship into a simple number like that of the budget might catalyze the process of rhetorical entrapment.