Global environmental issues are moving up the international political agenda. Climate change, in particular, is now widely recognized as one of the greatest challenges facing the international community in the twenty-first century.

Until recently, the very occurrence of anthropogenetic climate change was still a matter of political dispute. But now, even as ideologically driven skepticism abates about whether dangerous climate change is occurring, we are brought to consider alarming new scientific findings about the possible nature of the change. As Stephen Gardiner opens by observing, as recently as the 2001 report of the Intergovernmental Panel on Climate Change, the problem was still viewed as a matter of gradual, incremental effects. However, greater attention is now being focused on the possibility of “encountering major threshold phenomena in the climate system, where breaching such thresholds may have catastrophic consequences.” Gardiner's article explores the possibility that awareness of such stark and dramatic threats could actually serve to break the political inertia that continues to hold back the implementation of measures that would be adequate to dealing with the problem as scientists present it. However, he thinks there are reasons to be skeptical and cautious about such a prospect: for the possibility of abrupt change might only reshape rather than undermine the usual concerns, and it might even make appropriate action more rather than less difficult to achieve. “Worst of all, if the abrupt change is severe, it may provoke the equivalent of an intergenerational arms race.” The “intergenerational arms race” has structural similarities to debt deflation. The longer you put off dealing with the problem, the harder it becomes to deal with it; and the harder it is to deal with, the stronger your incentive to put off dealing with it. Gardiner concludes we have to look beyond people's generation-relative preferences; the hope he holds out is that contemplating the possibility of abrupt change will help us engage intergenerational motivations. If severe abrupt climate change is a real threat, the time for action is now, when many actions are likely to be prudentially and morally easier than in the future.

It seems that we need to appreciate, therefore, the sense in which our generation is enjoying a “free ride” at the expense of future generations. The article by Simon Caney contributes to our understanding of the nature of this intergenerational collective action problem with his critical analysis of the reasons why the present generation might feel justified in applying a positive social discount rate and devoting more resources to our contemporaries than to future generations. One of the standard justifications for discounting the future is the argument that it would be wrong to take on the expense of mitigating on behalf of future generations because they will be better off than us. Of course, it is a matter of contention whether future generations really will be better off than us—especially if they face the costs of unabated climate change—but Caney argues that, even granting that contentious assumption, the conclusion does not follow. Nor, he argues, can discounting be justified on the grounds that future risks and/or uncertainties—in virtue of their indeterminable probability—place a lesser call on our current resources than do our manifest contemporary problems. This issue is at the heart of contestation about the appropriate meaning and application of the Precautionary Principle. Caney's innovative argument aims to show how a justification for precaution can be derived from analysis of how climate change jeopardizes fundamental human rights. A human rights-oriented approach gives us good reason to reject “time” discounting, “growth” discounting, and “risk and uncertainty” discounting, he argues, and strengthens the case for an aggressive policy of mitigation and adaptation dedicated to preventing rights-jeopardizing climate change.

The context of abrupt climate change and the question of how to justify precaution are brought together by Catriona McKinnon. In virtue of the prospect of runaway climate change precipitated by passing various “tipping points” of abrupt change, Mackinnon argues that a precautionary approach ought to be adopted by policy-makers. Noting that the Precautionary Principle admits of stronger and weaker interpretations, and that a strong interpretation is indefensible as a general principle for policy-makers, she argues it is nevertheless defensible with respect to climate change, against the background of a commitment to deliver justice to future generations. Understanding intergenerational justice in broadly Rawlsian egalitarian terms, she distinguishes two Rawlsian arguments for taking precautionary action against the worst outcomes of climate change. One would make reference to the unjust distribution of advantage across generations that could be caused by failing to take precautions. The maximin principle supports strong precaution because the worst consequences of not taking precautionary action are worse than the worst consequences of taking it. On balance, though, she believes a more powerful argument would make reference to the “unbearable strains of commitment”: for the consequences of failing to take precautionary action could be such extreme scarcity of resources and almost unimaginably bad living conditions that the joint pursuit of justice would be rendered impossible. If not taking precautions could cause such circumstances for future generations, then we cannot choose not to take them.

The matter of intergenerational justice is further complicated, however, by questions of intra-generational justice. Although climate change is likely eventually to affect everyone—and that may be the reason why, of all global challenges of environment and justice, it is the one to have most galvanized attention—the costs of dealing with it are likely to have greater impact on the lives of the poor among future generations, just as they already do on the poor of the current generation. Furthermore, those who suffer most from the effects of climate change are generally among those who have benefited least from its primary cause, namely, the emission of CO2 into the atmosphere. Darrel Moellendorf, accordingly, stresses a need for sensitivity to how the intra-generational assignment of the costs of mitigation and adaptation bears on the just assignment of intergenerational costs of climate change. Adapting a broadly Rawlsian approach to model deliberative intergenerational impartiality, he develops a sophisticated account of a principle that assigns proportionally equal intergenerational costs, and addresses potential objections to it—including against Parfit's nonidentity problem. Something Moellendorf's argument serves to show is that if there were today a serious global commitment to progressively reducing unjust inequalities over time, this might be some justification for funding present reforms at the expense of future mitigation—since that would mean institutions were being directed toward well-being of the future poor too. But because that condition is counterfactual, the principle of Intergenerational Equality remains more justifiable than the alternatives discussed.

Robin Attfield explores how these concerns about the complex interplay of issues of intra- and intergenerational justice require us to reconceive the scope and content of ethics as more traditionally conceived. Taking his bearings from Hans Jonas's “imperative of responsibility,” he examines the difficulties—particularly those highlighted by Parfit—of how ethics can be adapted to deal with the full range of the foreseeable impacts of our present activities. Attfield's central theme is that of “mediated responsibilities.” These arise where there is a distance, spatial or temporal, between an action and its foreseeable impacts, and Attfield seeks to show that moral accountability attends causal responsibility as much when it is mediated as when it is unmediated. One particular area of responsibility is captured by the idea of “ecological debt,” whereby rich countries make disproportionate use of ecological space. This idea is explicated by reference to equal entitlement to environmental capacities—which, he believes, could be supported on either consequentialist or Kantian grounds. But this means the framework of decision making needs to be able to track current dispersed responsibilities for distant and future consequences: Governments as well as individuals need to recognize their mediated responsibilities.

A specific proposal that links individual responsibility to the wider issues of climate change, and addresses governments' responsibility for intra-national allocation, is that of personal carbon allowances (PCAs). Keith Hyams provides an introduction to this relatively new policy idea and discusses the various questions of ethics and justice it gives rise to. Philosophical questions about the distribution of PCAs focus particularly on how to allocate PCAs to individuals and whether they should be tradable. Answers will be influenced by what we take to be the rationale for PCAs as a policy option. He argues that it is in virtue of considerations of fairness that PCAs are a better policy option for reducing a country's carbon emissions than the obvious alternatives of either tax or industrial quotas. The task facing those who are moved by this rationale is to identify the norm that should regulate the fair introduction of PCAs into the market. In particular, we ought to examine the normative merits of proposals that mirror methods already used, or widely supported, to regulate the distribution of emission rights to states or industrial firms. We should not assume, though, that the normative principles applicable to the international case will automatically apply in identical fashion to intra-national contexts.

The capacity of the earth's atmosphere to absorb carbon emissions is one (very significant) component of what may, more comprehensively, be described as “ecological space.” Steve Vanderheiden argues that recognition of the finitude of ecological space “may invalidate many other longstanding normative commitments from the liberal canon, forcing us to rethink judgments reached on the basis of obsolete premises in light of a more realistic set of assumptions.” He claims that while cosmopolitan justice theories—like those of Beitz and Pogge—have begun to display some recognition of ecological limits, they need to go further. We need to take seriously how ecological limits potentially constrain economic development and we should thus suspend cornucopian assumptions supporting a belief that growth of production and consumption in developing countries can be sustainable in the absence of economic contraction in industrialized ones. The principle of “contraction and convergence” that cosmopolitan climate justice advocates have promoted with respect to global greenhouse gas emissions should apply more generally to the world's resources. We need to understand the causal role that uninhibited individual autonomy in consumption choices can play in causing ecological harm half a world away. The sphere of unconstrained liberty shrinks considerably once ecological limits are taken into account: for relevant to each person's ability to exercise control over their personal space of autonomy is the restraint exercised by others in their own.

Tim Hayward's contribution picks up on these themes to press critical questions against the widespread presumption that cosmopolitanism represents a continuation of liberal theories of justice. He points out the tension within liberalism between its progressive ideals and the ideological service it supplies for a capitalist economy. If this tension is not generally regarded as a serious problem within the context of a liberal nation-state, he thinks it nevertheless has significance in the context of the new global challenges. Regarding global justice, he suggests that the liberals who are most consistent in their thinking are those who, like Rawls, resist the claims of cosmopolitanism. If so, a consistent account of cosmopolitanism involves something other than an extension of liberalism. Regarding the global environment, he suggests that the aim of sustainable development has been readily endorsed by liberals because of its optimistic implication of a potential win-win-win scenario for protecting the environment while also securing economic development and promoting global justice. Yet if we attend to the losses and costs associated with this development model, we may find it more appropriate to reframe the aims relating to global environmental justice in terms of ecological debt. This is to challenge liberal theorists either to defend the cornucopian assumption or to think through the full consequences of dropping it. These include asking how progressive in fact is a distinctively liberal construction of ethical goals in the contemporary circumstances of global justice. He suggests that what present circumstances require is an ethos of restraint and that this, in key respects, is the antithesis of a liberal ethos.

In any event, the question of what global justice requires in the light of ecological constraints, on the one hand, and the imperatives of human rights, on the other, is revealed by the present collection of articles to be as intellectually challenging as it is practically urgent.