Runaway Climate Change: A Justice‐Based Case for Precautions
2009; Wiley; Volume: 40; Issue: 2 Linguagem: Inglês
10.1111/j.1467-9833.2009.01446.x
ISSN1467-9833
Autores Tópico(s)Risk Perception and Management
Resumo[T]he existing estimates of [the] social cost [of climate change] are based on IPCC studies that so far have not included many . . . irreversible positive feedbacks. . . . So nobody has yet even asked what price should be attached to a century-long drought in the American West, or an enfeebled Asian monsoon, or a permanent El Niño in the Pacific, or a methane belch from the ocean depths, or a collapse of the West Antarctic ice sheet, or sea levels rising by half a yard in a decade. Though, on reflection, these are perhaps questions not best answered by accountants.1 The basic science of climate change (CC)—our understanding of the way in which greenhouse gases (GHGs) warm the planet—is well established and understood. However, experts still have limited understanding of the nature and significance of various positive and negative feedback effects that could respectively accelerate or slow CC, and there is much disagreement among them about the accuracy and reliability of the models positing these effects, and/or the existence of data sets adequate to support their prediction. In particular, the possibility of powerful positive feedbacks is increasingly being taken by many experts to undermine the "gradualist paradigm" in thinking about CC, most notably as adopted by the Intergovernmental Panel on Climate Change (IPCC).2 According to this paradigm, the changes constitutive of CC are cumulative, smooth, and incremental, which makes them easier to predict and plan for. However, challenges to this paradigm have it that CC might happen through a combination of gradual changes and some very abrupt shifts, as we pass various "tipping points." These events are points of no return, beyond which positive feedbacks causing runaway CC create a world not represented in any IPCC scenarios, and beyond the scope of much scientific imagination to date. The possibility of passing tipping points on the way to CC catastrophe (CCC) has led some normally cautious scientists to adopt the language of Armageddon in their attempts to get these possibilities into the public debate about CC; for example, NASA scientist James Hansen describes the current state of affairs as "a planetary emergency."3 There are numerous significant tipping points, and new ones are emerging all the time.4 To provide focus, I shall limit discussion to a set of frightening positive feedbacks that scientists have awakened to only recently. Fifty-five million years ago the Earth experienced a period of extreme and accelerated warming called the Paleocene-Eocene thermal maximum (PETM), which triggered the largest mass extinction event since the "Great Dying" 251 million years ago (in which ninety-five percent of species went extinct). Many scientists believe that the PETM was largely caused by the release of trillions of tons of methane from beneath the oceans. This methane had been trapped in frozen, honeycombed sediments called "clathrates," and was released as a result of global warming (probably caused by solar activity). At present, one to ten trillion tons of methane clathrates exist beneath the world's oceans, and could be destabilized by the rapidly warming oceans. The release of even a fraction of this methane could be catastrophic in at least two ways. First, it could cause massive underwater landslides that would create tsunamis comparable in size with, or larger than, the one that started in the Indian Ocean on December 26, 2004. Indeed, scientists now believe that the "Storegga slip" eight thousand years ago—which occurred off the coast of Norway and caused a tsunami of forty feet in Norway, twenty feet in Scotland, and sixty feet in the Shetlands—was caused by the explosive release of methane from a destabilized clathrate. Second, the release of methane on this scale could cause runaway CC from which it would be impossible to recover, given existing levels of anthropogenic warming;5 it is not science fiction to claim that in these conditions temperature increases could exceed 6°C (see section 4 for more detail). In this scenario the majority of life on Earth, perhaps including homo sapiens, could go extinct.6 Call this scenario "Methane Nightmare." I shall argue that a precautionary approach ought to be adopted by policy-makers addressing CC in virtue of the possibility that CC could cause us to pass key tipping points beyond which positive feedbacks are activated that could cause runaway and catastrophic CC. I shall present arguments for the Precautionary Principle (PP) as the approach to CCCs that should be adopted by policy-makers concerned (as they should be) with intergenerational justice, and I shall understand intergenerational justice in broadly Rawlsian egalitarian terms. What I mean by this is that it is appropriate to adopt Rawls's conceit of the original position when thinking about intergenerational justice. The impartiality modeled by this method for choosing principles of justice is required not only between members of the same generation, but also across members of different generations. Rawls incorporates this commitment into his hypothetical social contract by stipulating that intergenerational justice is to be governed by his "Just Savings" principle.7 Parties behind the veil of ignorance are to be thought of as contemporaries: they belong to the same generation (and know this), but they do not know which generation this is. He calls this the "present time of entry" interpretation of the original position.8 In this situation, parties would adopt a "maximin" rule to govern their choices between different sets of principles and, for Rawls, this holds with respect to intergenerational as well as intragenerational justice.9 Of course, there are few, if any, policy-makers whose decisions conform to, or whose reasoning reflects, Rawls's conception of intergenerational justice. But even if the non-ideal world of non-compliance with principles of justice endures forever, it still matters that we recognize the ways in which the world is unjust and could be made better. The defense of the PP offered herein is a (small) part of that endeavor as applied to the worst effects of CC on human social and political organization, with particular reference to its intergenerational aspect. In this paper, I shall distinguish between two Rawlsian arguments for taking precautionary action against the worst outcomes of CC. I shall show that although both arguments provide compelling grounds for taking such action, the argument making reference to the "strains of commitment" is more powerful than the argument making reference to the unjust distribution of advantage across generations that could be caused by failing to take precautions against CCCs. One feature of CCCs that makes policy making with respect to them so difficult is that they are uncertain. In one basic sense, the meaning of "uncertainty" is clear: that which is uncertain is not certain. Given that nothing in the future is certain, and given that all policy is future-oriented, uncertainty (in this basic sense) is integral to the context of every policy decision. Uncertainty in this sense does not pose a special problem for policy-makers because it is consistent with a future event being uncertain that it is assigned a probability of happening (indeed, probability is a way of expressing uncertainty), and once a policy-maker has this information she can perform a standard risk assessment to guide her thinking about the event by multiplying its probability by its costs or impact. This is not the sense in which CCCs are uncertain. Rather, although CCCs are known to be possible (often because they have happened in the past), the processes that cause them are so poorly understood that it is not possible to assign a precise numerical probability to them, and thus a risk assessment cannot be made.10 Clive Spash's typology of uncertainty as "weak" and "strong" is helpful here.11 Weak uncertainty exists when outcomes and their probabilities (understood either as objective features of the world, or as subjective insofar as derived from persons' preferences) are known. The context for much policy making is weak uncertainty, and the dominant approach to policy making in this context is risk assessment. Strong uncertainty exists when outcomes are unknown and/or unpredictable, either because the outcomes are indeterminate, or because the state of knowledge with respect to these outcomes precludes the assignment of a probability to them. The strong uncertainty of CCCs renders them an elephant in the room in CC policy debates. Of course, some GHG reduction targets—for example, the UK's commitment to cut CO2 by sixty percent by 2050—can be read as addressed to CCCs just in virtue of the fact that any reduction in GHGs can be seen as an attempt to mitigate CC, CCCs included. But such policies are certainly not justified by direct reference to mitigating CCCs; and a cut of sixty percent (let alone the paltry Kyoto targets) is unlikely to do the job. Furthermore, as already noted, the bibles of policy-makers addressing CC—the IPCC Reports—do not include CCCs in their scenario analyses, and work largely within the gradualist paradigm. The unavailability of risk assessment as a method for policy making with respect to strongly uncertain CCCs has led an increasing number of thinkers (even those generally sympathetic to cost–benefit analysis, of which risk assessment is an example)12 to give serious consideration to the PP as a guide to policy making for such events.13 The PP is sometimes presented as equivalent to, or derived from, the principle "better safe than sorry." So presented, it is hard to refute: Who would rather be sorry than safe? However, these presentations are inaccurate to the PP as it appears in policy documents.14 Rather, the PP removes constraints on reasons for action in policy making where scientific expertise is indispensable: It states that strong uncertainty about harm need, or must, not stand as a reason for inaction with respect to policy making that would adequately protect people from these harms. The principle has a weak and a strong formulation. The weak PP: When evidence or information is insufficient to establish the nature and/or probability of harms caused by an activity, policy-makers are permitted to act in order adequately to protect people and other entities from these possible harms. The strong PP: When evidence or information is insufficient to establish the nature and/or probability of harms caused by an activity, policy-makers are required to act in order adequately to protect people and other entities from these possible harms. The weak PP (WPP) is a permissive principle: It states the reasons on which it is acceptable for policy-makers to act. The WPP permits policy-makers to take preventive action for reasons other than certainty that the action is necessary to prevent a harm. The strong PP (SPP) is a categorical principle. It states the reasons upon which policy-makers must act; that is, in order to protect people and other entities from possible harms, even when the nature and/or probability of these harms is not known. Given this uncertainty, reasons given in justification of action taken in the name of the SPP must appeal to considerations other than those of evidence- or model-based support for the belief that the action is necessary to prevent a harm. It is relatively rare to find examples of the SPP in policy literature; far more common are varieties of the WPP.15 The WPP is impotent as a constraint on the decisions of policy-makers because it is satisfied even if decision making on every policy issue in its scope is postponed until the relevant evidence and information is certain; that is, even if no policy-maker ever actually takes precautionary measures as set out in the WPP. When one does not do P despite having permission to do P, one acts consistently with that permission. Including the WPP in policy documents need have no impact at all on any commitments appearing elsewhere in them, or in any other documents.16 For this reason I shall focus instead on the SPP. This is a steely principle: It compels policy-makers to act in the face of strong uncertainty even though their action may in fact turn out to be an unnecessary precaution against a non-existent, or vanishingly unlikely, harm. Because such action is almost always expensive(in literal sterling terms), and costly (in terms of the intrusiveness, disruptiveness, and unpopularity of legislation to satisfy the principle, and its impact on other policy commitments), the SPP is generally dismissed as an unworkable and naïve proposal made by those in the grip of an ideology or suffering from distorted perceptions of risk. One way of arguing for the SPP with respect to CCCs is with the claim that the SPP ought to be adopted by policy-makers in general when framing legislation for processes that create uncertain risks of harm. It is clear that this sweeping claim is a non-starter: As Sunstein puts it, "[t]he regulation that the principle requires always gives rise to risks of its own . . . hence the principle bans what it simultaneously mandates."17 Applied at this level of generality, the SPP is literally incoherent: each course of action it requires of policy-makers it simultaneously prohibits.18 Although the SPP is indefensible as a general principle for policy-makers, it is nevertheless defensible with respect to CCCs, against the background of a commitment to deliver justice to future generations. In the next section I lay out a Rawlsian argument that makes this case, and I comment on its limitations. In section 4 I develop a second (and new) Rawlsian argument which is not subject to these limitations, and which delivers a more potent justification of the SPP with respect to CCCs. Famously, Rawls offers an interpretation of equality as maximin: to treat people as equals means (among other things) to ensure a distribution of (dis)advantage among them that makes the worst-off group as well off as possible. In addition, Rawls conceives of justice as intergenerational in scope, governing relations across generations as well as within them. These commitments can be made to work to justify the SPP with respect to CCCs as follows. The SPP is justified with respect to CCCs because the worst consequences of not taking precautionary action are worse than the worst consequences of taking precautionary action, and choosing the former course of action is not consistent with treating present and future people as equals when we cannot assign a probability to each outcome, that is, when we are strongly uncertain of each outcome, as is the case with respect to CCCs. We can see this by adopting the Rawlsian conceit of the original position, and by imagining what parties choosing principles therein would say in justification of their choices to those whose interests they represent. What such persons could not do is to take a bet on the probability of the worst consequences of no precautions being lower than the probability of the worst consequences of precautions, given the nature of these consequences. Call this the "playing safe" argument; in order to make it in full I need to specify in more detail the nature of the consequences in question.19 The worst consequences of taking precautions against CCCs are that the costs of adapting to CC turn out to be lower than the costs of taking precautions. The consequences of CC may turn out to be nowhere near as dire as experts' worst fears, and it may be that tipping points and their CCCs exist only in nightmares and Hollywood movies, or are extremely distant in time, giving us more opportunity for cheaper precautionary action at a later date. It may be that the Earth is far more insensitive to our activities than we think. In this scenario, we spend a lot of money and time—with all the associated opportunity costs this creates—in taking precautions against consequences now that are in fact not necessary. Estimates of how much it would cost to implement adequate precautions vary widely; for example, Bjorn Lomborg puts the figure at $37.632 trillion, whereas the European Commission (working with a generous stabilization target of 550 ppm to be met by 2100) chooses $1–8 trillion,20 and the Stern Review estimates the cost at one percent of the world GDP in 2050, or $1 trillion.21 These figures are hotly disputed, but to make the case against precautions as powerful as possible I shall adopt the Lomborg estimate. Call this outcome "Unnecessary Expenditure." The worst outcome of not taking precautions is that the worst predictions of the IPCC turn out to be very conservative,22 that the gradualist paradigm is false, and that we are on the verge of various tipping points, with everything this entails. The worst outcome of a decision not to take precautionary measures with respect to CC is catastrophic ala Methane Nightmare. With these outcomes identified, the playing safe argument from maximin for the SPP with respect to CC is prima facie powerful: Because Methane Nightmare is so much worse than Unnecessary Expenditure, we ought not to act as if the worst case scenario of taking precautions is more probable than this worst case scenario of not taking precautions, and thus we ought to take precautions against CCCs. Acting as if the worst consequences of taking precautions are more probable than the worst consequences of not taking precautions is ruled out because the harms that would be caused to present and future people by policy made on this assumption, if it turns out to be false, are much greater than the harms that would be caused by policy made on the first assumption, if this turns out to be false. And treating people as equals makes it impermissible to gamble with their interests in this way. Stephen Gardiner's elaboration (following Rawls) of the conditions under which Rawlsian maximin reasoning delivers the requirement to take precautions is helpful.23 These are when (i) decision makers are in a state of strong uncertainty with respect to the probability of the events in question; (ii) decision makers are indifferent to gains above the minimum that a maximin strategy would guarantee; and (iii) the alternatives to a decision guided by maximin are unacceptable.24 We have seen that (i) is true of CCCs (I shall consider objections to this claim in section 5). Conditions (ii) and (iii) are questioned when it is claimed that it is rational or reasonable to gamble on the probability of Unnecessary Expenditure being higher than Methane Nightmare—and so not to take precautions—because if this gamble pays off the gains are so much higher than if the bet is not placed at all, or is placed on the probability of Methane Nightmare being higher than Unnecessary Expenditure.25 Call this the "skeptical stance." There are two comments on the skeptical stance. First, it does not take seriously the possibility that even if the bet at its heart were to turn out to be good, we may still have reason not to make it in virtue of how taking precautions against CCCs could have all sorts of other benefits that would make this choice attractive even if any CCC turns out to be highly improbable. This is the so-called "no regrets" strategy: the requirement to take precautionary measures against CCCs could stimulate technological innovation, efficiency measures, and new forms of political interaction that could greatly enhance the quality of our lives even if the precautions turn out to have been redundant with respect to CCCs. In other words, the opportunity costs created by not taking precautions might make it always less costly to take precautions, even taking into account the possibility that the probability of any CCC is tiny. Although the "no regrets" strategy is not part of Rawlsian maximin and so, strictly speaking, not part of the playing safe argument, it is certainly not inconsistent with it; indeed, it could be proposed as an interpretation of condition (iii) above: not taking precautions is an unacceptable alternative not only because of the possibility of CCCs, but also because of the possible gains associated with precautionary measures. Of course, whether taking precautionary action against CC is a no regrets strategy is highly controversial. Hence, if there is an alternative, or complementary, way to undermine the skeptical stance, then all to the better. This brings me to my second comment, which relates to the type of justice to which the playing safe argument as it stands appeals. The argument is that CC policy-makers concerned to treat persons (always remembering that this includes future generations) as equals should be guided by the maximin rule to take precautions against CCCs, because Methane Nightmare is much worse than Unnecessary Expenditure. In what ways, exactly, is Methane Nightmare worse than Unnecessary Expenditure? Clearly, there are all kinds of losses—in biodiversity, to ecosystems, of habitats—that would occur under Methane Nightmare but not under Unnecessary Expenditure. Let me put these to one side in order to focus on a harm people in Methane Nightmare would suffer that people in Unnecessary Expenditure would not. In Unnecessary Expenditure we waste resources that could have been used to improve the position of the worst off in the current generation or, indeed, that could have been saved for the benefit of the worst off in future generations. These are considerations of distributive justice, and in line with the impartiality at the heart of the Rawlsian approach to justice, duties of distributive justice are intergenerational in scope.26 If we have a duty to ensure that the worst off—understood in intergenerational terms—are as well off as possible, and if Unnecessary Expenditure conflicts with this duty, then we have a reason to reject courses of action leading to it, and should avoid it, all else being equal. The playing safe argument as presented so far can be read as claiming that all else is not equal: the distributive injustice that would be created by Methane Nightmare is worse than that created by Unnecessary Expenditure, and we must choose between courses of action to which Unnecessary Expenditure and Methane Nightmare attach as worst outcomes, in which case we should aim to avoid the worst worse outcome—that is, Methane Nightmare—by taking precautions. Any disadvantage that accrues to the worst off as a result of this choice is justifiable to them in the name of equality: Given the badness of Methane Nightmare, choosing not to take precautions—given our uncertainty—would be to gamble with their interests by betting on the probability of Methane Nightmare being lower than that of Unnecessary Expenditure. However, as we have seen, making the argument in terms of distributive justice leaves it vulnerable to the skeptical stance, as follows. This version of the argument turns on the requirement to ensure that the worst-off generation is as well off as possible in terms of tangible goods, which includes generations in the future who may suffer huge disadvantage if we do not take precautions against CCCs. It can then be objected that tangible goods can be priced, and that the cost of taking precautions now will make these goods unaffordable for future generations. People who take the skeptical stance characteristically specify why it is rational or reasonable to gamble on the probability of Unnecessary Expenditure being higher than Methane Nightmare (and so not to take precautions) in terms of monetary gains and losses: crudely, we will be richer, and make future generations richer, if we do not take precautions. Of course, most people who take this tack also insist that monetary gains and losses matter because we can do things with money, such as improving human health.27 However, as has been observed frequently, there are things we value (or ought to value) which cannot be compared in value to other valuable things, and so are not amenable to being priced. Consequently, such incommensurably valuable things do not appear in the calculations that inform rejection of precautionary approaches such as this.28 One of these things is intergenerational justice.29 The playing safe argument as made so far is limited to a conception of intergenerational justice in distributive terms. However, there is another way to make the playing safe argument that articulates the impermissible gamble at its heart in terms of a more fundamental vision of what intergenerational justice requires, and evades the skeptical stance. I make that argument in the next section. There is something bad about Methane Nightmare that is related to justice, but is not well captured in terms of distributive justice, and which is absent in Unnecessary Expenditure. Highlighting this feature of Methane Nightmare makes available to us an extra reason for taking precautions against CC that justifies this choice not just in virtue of an egalitarian commitment not to gamble with the interests of the worst off in accumulating as many tangible goods as possible, but also in virtue of a commitment to making it possible for future people to commit themselves to justice at all. This additional badness turns on the fact that Methane Nightmare would create unbearable strains of commitment for those living through and after it: it would make unreasonable any mutual expectations among future generations that they should propose and abide by fair principles of justice.30 If this would be true of future generations in Methane Nightmare, then we—the current generation—cannot adopt principles for action on CC that could have this outcome. The strains of commitment are related to the idea of making an agreement in good faith; in Rawls's words, "not only with the full intention to honour it but also with a reasonable conviction that one will be able to do so."31 Rawls claims that excessive strains of commitment cause people to withhold affirmation of principles of justice in two ways. First, people "become sullen and resentful . . . ready as the occasion arises to take violent action in protest against [their] condition"; and second, people "grow distant from political society . . . withdrawn and cynical [they] cannot affirm the principles of justice in . . . thought and conduct over a complete life."32 Any attempt to implement principles of justice in Methane Nightmare—and many other CCCs—would probably have these effects on people. An indication of the temperature rises that might be experienced in Methane Nightmare is available by looking back at the PETM, to which it is thought that the collapse of methane clathrates greatly contributed.33 In this period, average temperatures increased by 5–10°C.34 One of the few models that address the effect of a global temperature rises of 5°C predicts severe desertification in already arid regions35—decimating most of the world's breadbaskets—combined with huge increases in precipitation at higher latitudes, making floods and storms more frequent.36 The net result of a 5°C increase would be worldwide famine, severe conflict over water in the world's desertified regions, and extreme territorial insecurity for those living in the dwindling inhabitable areas as an archipelago of refuges is put under increasing pressure by hungry and desperate people.37 At a 6°C increase, however, things likely become very much worse. Mark Lynas suggests that the best reference point for this amount of warming is not the PETM, but rather the end of the Permian era 251 million years ago, when the "Great Dying" extinction event, which wiped out ninety-five percent of the planet's species, occurred as a result of a temperature increase of 6°C.38 At the Permian-Triassic boundary, the oceans heated drastically and became devoid of oxygen, and so unable to support life, and also spawned superhurricanes which distributed heat to the poles (a further positive feedback).39 Destabilized methane clathrates beneath the oceans released huge quantities of CH4 which, if ignited, would have generated explosive, lethal blast waves traveling at two kilometers per second, and killing everything in their path.40 The rotting carcasses of animals, and decaying vegetation, in the oceans released large amounts of hydrogen sulphide, obliterating any remaining life there,41 killing most remaining land animals when released into the atmosphere,42 and destroying the ozone layer. For temperature rises beyond 6°C, predicting the effects is guesswork, but looking to conditions on Venus gives some indication. It is crucial to note that the temperature increases that caused the Great Dying probably took ten thousand years to effect, whereas—even on the conservative estimates of the IPCC—we could achieve such warming in one hundred years. As Lynas puts it, "[i]f we had wanted to destroy as much of life on Earth as possible, there would have been no better way of doing it than to dig up and burn as much fossil hydrocarbon as we possibly could."43 The extreme scarcity of resources and almost unimaginable conditions in Methane Nightmare would make the joint pursuit of justice impossible.44 When there is not enough for each to have even the bare minimum for survival, to ask anyone to do anything other than pursue their self-preservation and perhaps that of their family—such as to act according to the demands of justice—is to ask them to accept death so that others can live. In normal circumstances, the sacrifices in self-interest required by justice are not unreasonable and, all else being equal, do not impose unbearable strains of commitment on those on whom they fall. But in circumstances as desperate as Methane Nightmare, where self-preservation dominates all other motivations, any justice-based request for self-sacrifice will at least endanger a person's chances of survival, if not actually require their death. What makes this request an unbearable
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