Which principles should be the bases of our decisions about how to respond to climate change? It is a ubiquitous question, almost a banality, but nevertheless an important one. It has plagued debates about climate change since its emergence as a problem in the late 1980s; differences between particular responses can be traced back to differing underlying assumptions about which normative principles are appropriate and justifiable.

The books under review provide exemplary expressions of two specific ways to respond to this question. Both are engaging, well written, clearly structured, and cogently argued. Both set out their assumptions clearly and proceed carefully to conclusions, taking on the various objections explicitly. But both present dramatically different accounts of the basis on which we should proceed.

William Nordhaus has been prominent in debates within economics about climate change since the early 1990s. A Question of Balance is the presentation of the data from the latest version of his model, known as DICE (dynamic integrated model of climate and the economy). His purpose is to design a model that describes the main elements of those parts of the economy relevant to greenhouse gas emissions, as well as the principal dynamics of the climate system. He can thus ask questions of the model to determine what would be the outcome—in terms of rates of emissions, warming, costs of impacts, and abatement measures—of different types of policy responses. His normative frame of reference is, very explicitly, economic optimization; he seeks to defend policies that generate the lowest overall costs to the global economy.

The book develops the assumptions in the model, describes how it is constructed, and then offers a number of runs of the model with variations in some key assumptions. Nordhaus then discusses some debates about key issues that affect differing assessments among economists concerning climate change policy. These discussions center on the question of how broad participation in a climate regime needs to be in order to get an optimal response (Chapter 6); how to deal with the various uncertainties in the models (Chapter 7); the advantages of carbon taxes over other policy tools (Chapter 8); and the question of the appropriate discount rate (Chapter 9), especially given the debate over this question in relation to the well-publicized Stern Review (Nicholas Stern, The Economics of Climate Change, 2007).

Nordhaus is fully aware of the uncertainties that limit any model of climate–economy linkages. What is worth noting is that he resolves such uncertainties in a way that reduces the costs of climate impacts and increases the estimated costs of reducing emissions. This is clear in the way he deals with the discount rate, including his discussion of the Stern Review (e.g. pp. 61, 173, 181–84), the exogenization of technological change, and the possibility of catastrophic climate change. For the first, while his methodological critique of Stern is persuasive, his resolution—to use the real return on capital—only tells us how businesses discount the future, and not how society as a whole might do so. Regarding technological change, he is right that modelers find it very difficult to incorporate such change into models, but incorporating it would almost certainly reduce the projected cost of emissions reductions. And on catastrophic change, Nordhaus engages in sleights of hand to ignore taking this possibility seriously (see pp. 143–47). Whatever we think of his view on this question, it is clear that incorporating the possible costs of such extreme outcomes into his models would increase the benefits of reducing emissions by reducing the likelihood of such a consequence. The figure he gives about the “optimal” temperature increase (2.6°C by 2100) is considerably higher than what many consider a threshold that would trigger a number of possible positive feedbacks engendering such catastrophic changes.

While Nordhaus applies a particular normative framework—that of the pursuit of maximum aggregate utility—Steve Vanderheiden, by contrast, explores climate politics through the lenses of the whole panoply of ethical principles that Western philosophy has bequeathed us. The key concept arising in this context is that of justice, hence his title. Atmospheric Justice proceeds from general analysis of different concepts and aspects of justice (Chapter 2), to whether it can be applied across countries (Chapter 3), whether it can be applied across generations (Chapter 4), under what conditions it imposes specific moral responsibilities on individuals or other actors (Chapter 5), and whether and how such responsibilities are affected by the knowledge actors have of the consequences of their actions (Chapter 6). The style is dense but always readable, and the relevance of each specific philosophical point to specific aspects of climate change politics is always well drawn out.

Vanderheiden insists on the normative importance of justice, and his central question is whether particular levels of emissions abatement, and particular distributions of the costs of mitigation, are fair. According to this author, the approach of Nordhaus and most other economists—to simply find the “optimal” level of abatement for the world as a whole and to identify a means to reduce emissions efficiently—is insufficient. Most importantly, Vanderheiden shows powerfully that it matters greatly who has caused climate change and who, therefore, ought to play a disproportionate role in cleaning up the mess. But the utilitarian approach underpinning Nordhaus's arguments is also deficient, following Vanderheiden, in ignoring questions of rights that are central to questions of justice. The causal argument previously mentioned illustrates one such question of rights: the rights of some not to have their conditions of life endangered by the actions of others. But the rights question also extends to the distribution of emissions; why should some have access to more of the atmospheric commons than others? Taking these questions seriously would make accepting the approach of Nordhaus and other economists extremely difficult.

At the heart of the difference in approach is the monist ethics of economics—the treatment of aggregate utility as the sole judge of a “rational” approach—versus the ethical pluralism underpinning Vanderheiden's book, which insists that such utilitarianism is frequently indefensible. The problems of utilitarianism are well known in ethical debates, but Vanderheiden shows what sorts of ethical minefields are produced by a singular reliance on that framework when it comes to climate change. Three problems are particularly prominent.

First, utilitarianism effaces the differences between individuals. In the search for aggregate utility, Nordhaus, and others like him, produce models that deny the survival rights of some in the search for optimal rates of carbon emissions limitations. Put bluntly, it is optimal, in Nordhaus's models, that a greater number of people die than could be prevented. Vanderheiden shows very clearly why this is ethically insupportable.

Second, utilitarian theories fail to take account of inequalities among people. The optimal approach to climate change defended in Nordhaus's book involves the setting of equalized carbon taxes across the globe. The more universally applied, the more efficient the response, since all actors face the same incentives to limit their emissions. But Vanderheiden shows clearly that this “equal burdens” approach, in the context of huge inequality across the globe, would produce, in fact, considerable injustice for it fails to distinguish between “luxury emissions” and “survival emissions,” respectively, imposing the same penalty on behavior whether or not such behavior is discretionary.

Third, the utilitarian account focuses solely on the question of how to distribute a burden of limiting emissions across time and space. This abstracts completely from the question of fault and responsibility. Aggregating all emissions globally assumes that all have contributed to causing climate change, which is demonstrably not the case. As a useful corrective to this assumption Vanderheiden argues that coping with the impacts of climate change should be financed on the basis of past historic emissions, while limiting emissions in the future should be based on criteria of distributive justice. This is also a significant innovation in the literature on international climate justice (as well as the international negotiations themselves), which tends to conflate the two elements.

Taking justice seriously would in all likelihood result in considerably more aggressive efforts to limit emissions, as well as the means to share the burdens of climate change to which the world is already committed. While the actual political responses are influenced by many factors other than a concern either for economic optimality or for global justice, the ongoing debates about how the response should develop after 2012 are nevertheless shaped in part by these normative issues. These books do us a great service in helping to illustrate the implications of each type of approach and in making clear what is at stake in the debate between their proponents.