The Repugnant Conclusion is an implication of some approaches to population ethics. It states, in... more The Repugnant Conclusion is an implication of some approaches to population ethics. It states, in Derek Parfit's original formulation, For any possible population of at least ten billion people, all with a very high quality of life, there must be some much larger imaginable population whose existence, if other things are equal, would be better, even though its members have lives that are barely worth living. (Parfit 1984: 388)
All leading long-term global population projections agree on continuing fertility decline, result... more All leading long-term global population projections agree on continuing fertility decline, resulting in a rate of population size growth that will continue to decline towards zero and would eventually turn negative. However, a literature inspired by mathematical biology has suggested that because fertility is heritable (i.e., higher-fertility parents tend to have higher-fertility children) and heterogeneous within a population, long-term population growth must eventually be positive. In this research note, we show that heritable fertility is not sufficient for positive long-term population growth, for empirical and theoretical reasons. First, empirically, even higher-fertility sub-populations show declining fertility rates which may eventually be below replacement (and in some populations already are). Second, in a simple Markov model, because heritability is imperfect, the combination of heritability and fertility rates may be quantitatively insufficient: it may be that higher-fert...
The Oxford Research Encyclopedia of Economics and Finance, 2022
Nearly all large policy decisions influence not only the quality of life for existing individuals... more Nearly all large policy decisions influence not only the quality of life for existing individuals but also the number-and even identities-of yet-to-exist individuals. Accounting for these effects in a policy evaluation framework requires taking difficult stances on concepts such as the value of existence. These issues are at the heart of a literature that sits between welfare economics and philosophical population ethics. Despite the inherent challenges of these questions, this literature has produced theoretical insights and subsequent progress on variable-population welfare criteria. A surprisingly bounded set of coherent alternatives exists for practitioners once a set of uncontroversial axioms is adopted from the better-studied welfare criteria for cases where populations are assumed to be fixed. Although consensus has not yet been reached among these remaining alternatives, their recommendations often agree. The space has been sufficiently restricted and well explored that applications of the theoretical insights are possible and underway in earnest.
If non-human animals experience wellbeing and suffering, such welfare consequences arguably shoul... more If non-human animals experience wellbeing and suffering, such welfare consequences arguably should be included in a social welfare evaluation. Yet economic evaluations almost universally ignore non-human animals, in part because axiomatic social choice theory has failed to propose and characterize multi-species social welfare functions. Here we propose axioms and functional forms to fill this gap. We provide a range of alternative representations, characterizing a broad range of possibilities for multi-species social welfare. Among these, we identify a new characterization of additively-separable generalized (multi-species) total utilitarianism. The multispecies setting permits a novel, weak species-level separability axiom with important consequences. We provide examples to illustrate that non-separability across species is implausible in a multi-species setting, in part because good lives for different species are at very different welfare levels. Finally, we explore the consequences for evaluating climate policy and understanding speciesism and non-climate environmental goals, such as biodiversity.
At first glance, it may seem that climate policy based on estimates of the social cost of carbon ... more At first glance, it may seem that climate policy based on estimates of the social cost of carbon (SCC) presupposes a set of controversial assumptions, especially about what detailed knowledge regulators have about the impacts of climate change, and what the proper role of government and policy is in responding to those impacts. However, I explain why the SCC-based approach need not actually have these problematic presuppositions as well as why SCC estimates may provide the best guide to climate policy when implemented in a way that incorporates a healthy dose of humility. The SCC-based approach can be used in a way that is ecumenical between the wide range of reasonable but incompatible views about the proper goals of government and policy, ranging from views that aim only at market-efficiency, to utilitarian views, to rights-based and other deontological views, to libertarian views, to virtue ethics views, and others. Beyond this, I suggest that the SCC-based approach can help us find an overlapping consensus on a particular climate policy given the range of reasonable but incompatible normative views endorsed in diverse societies. Finally, I consider a number of specific objections to the SCC-based approach that are especially prominent in contemporary discourse and policy debates. I suggest that even if we agree that all of these objections to existing SCC-based analyses have an important kernel of truth, nonetheless the correct response to climate change still involves substantial emissions reductions to be achieved via policy, and the best methods for deciding the magnitude of those reductions still depend essentially on the SCC-based approach.
We find that if all countries adopt the necessary uniform global carbon tax and then return the r... more We find that if all countries adopt the necessary uniform global carbon tax and then return the revenues to their citizens on an equal per capita basis, it will be possible to meet a 2 °C target while also increasing wellbeing, reducing inequality and alleviating poverty. These results indicate that it is possible for a society to implement strong climate action without compromising goals for equity and development.
Existing estimates of optimal climate policy ignore the possibility that carbon tax revenues coul... more Existing estimates of optimal climate policy ignore the possibility that carbon tax revenues could be used in a progressive way; model results therefore typically imply that near-term climate action comes at some cost to the poor. Using the Nested Inequalities Climate Economy (NICE) model, we show that an equal per capita refund of carbon tax revenues implies that achieving a 2 °C target can pay large and immediate dividends for improving well-being, reducing inequality and alleviating poverty. In an optimal policy calculation that weighs the benefits against the costs of mitigation, the recommended policy is characterized by aggressive near-term climate action followed by a slower climb towards full decarbonization; this pattern—which is driven by a carbon revenue Laffer curve—prevents runaway warming while also preserving tax revenues for redistribution. Accounting for these dynamics corrects a long-standing bias against strong immediate climate action in the optimal policy literature.
Tools are needed to benchmark carbon emissions and pledges against criteria of equity and fairnes... more Tools are needed to benchmark carbon emissions and pledges against criteria of equity and fairness. However, standard economic approaches, which use a transparent optimization framework, ignore equity. Models that do include equity benchmarks exist, but often use opaque methodologies. Here we propose a utilitarian benchmark computed in a transparent optimization framework, which could usefully inform the equity benchmark debate. Implementing the utilitarian benchmark, which we see as ethically minimal and conceptually parsimonious, in two leading climate–economy models allows for calculation of the optimal allocation of future emissions. We compare this optimum with historical emissions and initial nationally determined contributions. Compared with cost minimization, utilitarian optimization features better outcomes for human development, equity and the climate. Peak temperature is lower under utilitarianism because it reduces the human development cost of global mitigation. Utilitarianism therefore is a promising inclusion to a set of benchmarks for future explorations of climate equity
The Repugnant Conclusion is an implication of some approaches to population ethics. It states, in... more The Repugnant Conclusion is an implication of some approaches to population ethics. It states, in Derek Parfit's original formulation, For any possible population of at least ten billion people, all with a very high quality of life, there must be some much larger imaginable population whose existence, if other things are equal, would be better, even though its members have lives that are barely worth living.
Reducing greenhouse gas emissions has the 'co-benefit' of also reducing air pollution and associa... more Reducing greenhouse gas emissions has the 'co-benefit' of also reducing air pollution and associated impacts on human health. Here, we incorporate health co-benefits into estimates of the optimal climate policy for three different climate policy regimes. The first fully internalizes the climate externality at the global level via a uniform carbon price (the 'cooperative equilibrium'), thus minimizing total mitigation costs. The second connects to the concept of 'common but differentiated responsibilities' where nations coordinate their actions while accounting for different national capabilities considering socioeconomic conditions. The third assumes nations act only in their own self-interest. We find that air quality co-benefits motivate substantially reduced emissions under all three policy regimes, but that some form of global cooperation is required to prevent runaway temperature rise. However, co-benefits do warrant high levels of mitigation in certain regions even in the self-interested case, suggesting that air quality impacts may expand the range of possible policy outcomes whereby global temperatures do not increase unabated.
What are the prospects for using population policy as tool to reduce carbon emissions? In this pa... more What are the prospects for using population policy as tool to reduce carbon emissions? In this paper, we review evidence from population science, in order to inform debates in population ethics that, so far, have largely taken place within the academic philosophy literature. In particular, we ask whether fertility policy is likely to have a large effect on carbon emissions, and therefore on temperature change. Our answer is no. Prospects for a policy of fertility-reduction-as-climate-mitigation are limited by population momentum, a demographic factor that limits possible variation in the size of the population, even if fertility rates change very quickly. In particular, a hypothetical policy that instantaneously changed fertility and mortality rates to replacement levels would nevertheless result in a population of over 9 billion people in 2060. We use a leading climate-economy model to project the consequence of such a hypothetical policy for climate change. As a standalone mitigation policy, such a hypothetical change in the size of the future population-much too large to be implementable by any foreseeable government programme-would reduce peak temperature change only to 6.4°C, relative to 7.1°C under the most likely population path. Therefore, fertility reduction is unlikely to be an adequate core approach to climate mitigation.
The population ethics literature has long focused on attempts to avoid the repugnant conclusion. ... more The population ethics literature has long focused on attempts to avoid the repugnant conclusion. We show that a large set of social orderings that are conventionally understood to escape the repugnant conclusion do not in fact avoid it in all instances. As we demonstrate, prior results depend on formal definitions of the repugnant conclusion that exclude some repugnant cases, for reasons inessential to any "repugnance" (or other meaningful normative properties) of the repugnant conclusion. In particular, the literature traditionally formalizes the repugnant conclusion to exclude cases that include an unaffected sub-population. We relax this normatively irrelevant exclusion, and others. Using several more inclusive formalizations of the repugnant conclusion, we then prove that any plausible social ordering implies some instance of the repugnant conclusion. This understanding-that it is impossible to avoid all instances of the repugnant conclusion-is broader than the traditional understanding in the literature that the repugnant conclusion can only be escaped at unappealing theoretical costs. Therefore, the repugnant conclusion provides no methodological guidance for theory or policy-making, because it does not discriminate among candidate social orderings. So escaping the repugnant conclusion should not be a core goal of the population ethics literature.
Deciding which climate policies to enact, and where and when to enact them, requires weighing the... more Deciding which climate policies to enact, and where and when to enact them, requires weighing their costs against the expected benefits. A key challenge in climate policy is how to value health impacts, which are likely to be large and varied, considering that they will accrue over long time horizons (centuries), will occur throughout the world, and will be distributed unevenly within countries depending in part on socioeconomic status. These features raise a number of important economic and ethical issues including how to value human life in different countries at different levels of development, how to value future people, and how much priority to give the poor and disadvantaged. In this article we review each of these issues, describe different approaches for addressing them in quantitative climate policy analysis, and show how their treatment can dramatically change what should be done about climate change. Finally, we use the social cost of carbon, which reflects the cost of adding carbon emissions to the atmosphere, as an example of how analysis of climate impacts is sensitive to ethical assumptions. We consider $20 a reasonable lower bound for the social cost of carbon, but we show that a much higher value is warranted given a strong concern for equity within and across generations.
Formal arguments have proven that avoiding the Repugnant Conclusion is impossible without rejecti... more Formal arguments have proven that avoiding the Repugnant Conclusion is impossible without rejecting one or more highly plausible population principles. To many, such proofs establish not only a deep challenge for axiology, but also pose an important practical problem of how policymaking can confidently proceed without resolving any of the central questions of population ethics. Here we offer deflationary responses: first to the practical challenge, and then to the more fundamental challenge for axiology. Regarding the practical challenge, we provide an overview of recent literature that explores the implications for public policy of the Repugnant Conclusion and related puzzles within population ethics, and shows that there is more commonality in the implications of different population axiologies than is generally recognized. The upshot is that uncertainty about population ethics presents no important problem for policymaking, and the importance of population ethics to policymaking has been overstated. We then turn to more fundamental issues about axiology, and describe a new series of formal proofs that undermine the idea that any plausible axiology could avoid the Repugnant Conclusion, including those that are assumed to avoid it in the literature. The philosophical upshot is that the Repugnant Conclusion cannot plausibly be avoided, and so it is a mistake to assume as a constraint on a plausible axiology that it must be avoided, as is assumed by most of the literature in population ethics, including by all of the fundamental impossibility theorems.
Choosing a policy response to climate change seems to demand a population axiology. A formal lite... more Choosing a policy response to climate change seems to demand a population axiology. A formal literature involving impossibility theorems has demonstrated that all possible approaches to population axiology have one or more seemingly counterintuitive implications. This leads to the worry that because axiology is so theoretically unresolved as to permit a wide range of reasonable disagreement, our ignorance implies serious practical ignorance about what climate policies to pursue. We offer two deflationary responses to this worry. First, it may be that given the actual facts of climate change, all axiologies agree on a particular policy response. In this case, there would be a clear dominance conclusion, and the puzzles of axiology would be practically irrelevant (albeit still theoretically challenging). Second, despite the impossibility results, we prove the possibility of axiologies that satisfy bounded versions of all of the desiderata from the population axiology literature, which may be all that is needed for policy evaluation.
The spectre of the repugnant conclusion and the search for a population axiology that avoids it h... more The spectre of the repugnant conclusion and the search for a population axiology that avoids it has endured as a focus of population ethics. This is in part because the repugnant conclusion is often interpreted as a defining problem for totalism, while the implications of averagism and related views are taken to illustrate the theoretical cost of avoiding the repugnant conclusion. However, we show that this interpretation cannot be sustained unless one focuses only on a special case of the repugnant conclusion: namely, the subset of instances of the repugnant conclusion where there is no portion of the population unaffected by the choice between population outcomes (as in Derek Parfit’s original illustration). To avoid an inappropriate focus on only this proper subset of instances of the repugnant conclusion, we formulate a general characterization of the repugnant conclusion. We then prove formally that all leading welfarist axiologies imply this conclusion, including averagism and Ng’s Theory X0 , including probabilistic and ‘very repugnant’ variants that involve the addition of negative lives. We then prove that the full range of axiologies considered by population ethics each imply an extended version of the repugnant conclusion, including axiologies that are incomplete, intransitive, rank-dependent, person-affecting, and/or pluralist. The upshot is that the repugnant conclusion does not ultimately tell against any approach to axiology, and the methodological requirement to avoid the repugnant conclusion should be dropped from population axiology.
The focus of this chapter is public policy and consequentialism, especially issues that arise in ... more The focus of this chapter is public policy and consequentialism, especially issues that arise in connection with the environment – i.e. the natural world, including non-human animals. We integrate some of the existing literature on environmental economics, welfare economics, and policy with the literature on environmental values and philosophy. The emphasis on environmental policy is motivated by the fact that it is arguably the most philosophically interesting and challenging application of consequentialism to policy, as it includes all the challenges of valuing the distribution of human wealth and power, and has the further challenge of putting these consequences on the same scale as consequences for human health, non-human animals, and nature. We suggest that standard methods of (economic) policy analysis provide a good approximation of correct welfarist analysis, except that they must be supplemented with methods for valuing animal wellbeing and tradeoffs with human wellbeing. We then provide the needed methods.
In this chapter, Mark Budolfson and Dean Spears analyse the marginal effect of philanthropic dona... more In this chapter, Mark Budolfson and Dean Spears analyse the marginal effect of philanthropic donations. The core of their analysis is the observation that marginal good done per dollar donated is a product (in the mathematical sense) of several factors: change in good done per change in activity level of the charity in question, change in activity per change in the charity’s budget size, and change in budget size per change in the individual’s donation to the charity in question. They then discuss the “hidden zero problem” that some of the terms in the equation (in particular, the last term) might be “hidden zeros” that prevent donations from doing any good—or worse, imply that they do harm—even if the charity is at the top of effective altruism rankings based on the other factors.
The health co-benefits of CO2 mitigation can provide a strong incentive for climate policy throug... more The health co-benefits of CO2 mitigation can provide a strong incentive for climate policy through reductions in air pollutant emissions that occur when targeting shared sources. However, reducing air pollutant emissions may also have an important co-harm, as the aerosols they form produce net cooling overall. Nevertheless, aerosol impacts have not been fully incorporated into cost-benefit modeling that estimates how much the world should optimally mitigate. Here we find that when both co-benefits and co-harms are taken fully into account, optimal climate policy results in immediate net benefits globally, overturning previous findings from cost-benefit models that omit these effects. The global health benefits from climate policy could reach trillions of dollars annually, but will importantly depend on the air quality policies that nations adopt independently of climate change. Depending on how society values better health, economically optimal levels of mitigation may be consistent with a target of 2 °C or lower.
Proceedings of the National Academy of Sciences, 2017
Future population growth is uncertain and matters for climate policy: higher growth entails more ... more Future population growth is uncertain and matters for climate policy: higher growth entails more emissions and means more people will be vulnerable to climate-related impacts. We show that how future population is valued importantly determines mitigation decisions. Using the Dynamic Integrated Climate-Economy model, we explore two approaches to valuing population: a discounted version of total utilitarianism (TU), which considers total wellbeing and is standard in social cost of carbon dioxide (SCC) models, and of average utilitarianism (AU), which ignores population size and sums only each time period’s discounted average wellbeing. Under both approaches, as population increases the SCC increases, but optimal peak temperature decreases. The effect is larger under TU, because it responds to the fact that a larger population means climate change hurts more people: for example, in 2025, assuming the United Nations (UN)-high rather than UN-low population scenario entails an increase in the SCC of 85% under TU vs. 5% under AU. The difference in the SCC between the two population scenarios under TU is comparable to commonly debated decisions regarding time discounting. Additionally, we estimate the avoided mitigation costs implied by plausible reductions in population growth, finding that large near-term savings ($billions annually) occur under TU; savings under AU emerge in the more distant future. These savings are larger than spending shortfalls for human development policies that may lower fertility. Finally, we show that whether lowering population growth entails overall improvements in wellbeing—rather than merely cost savings—again depends on the ethical approach to valuing population.
The Repugnant Conclusion is an implication of some approaches to population ethics. It states, in... more The Repugnant Conclusion is an implication of some approaches to population ethics. It states, in Derek Parfit's original formulation, For any possible population of at least ten billion people, all with a very high quality of life, there must be some much larger imaginable population whose existence, if other things are equal, would be better, even though its members have lives that are barely worth living. (Parfit 1984: 388)
All leading long-term global population projections agree on continuing fertility decline, result... more All leading long-term global population projections agree on continuing fertility decline, resulting in a rate of population size growth that will continue to decline towards zero and would eventually turn negative. However, a literature inspired by mathematical biology has suggested that because fertility is heritable (i.e., higher-fertility parents tend to have higher-fertility children) and heterogeneous within a population, long-term population growth must eventually be positive. In this research note, we show that heritable fertility is not sufficient for positive long-term population growth, for empirical and theoretical reasons. First, empirically, even higher-fertility sub-populations show declining fertility rates which may eventually be below replacement (and in some populations already are). Second, in a simple Markov model, because heritability is imperfect, the combination of heritability and fertility rates may be quantitatively insufficient: it may be that higher-fert...
The Oxford Research Encyclopedia of Economics and Finance, 2022
Nearly all large policy decisions influence not only the quality of life for existing individuals... more Nearly all large policy decisions influence not only the quality of life for existing individuals but also the number-and even identities-of yet-to-exist individuals. Accounting for these effects in a policy evaluation framework requires taking difficult stances on concepts such as the value of existence. These issues are at the heart of a literature that sits between welfare economics and philosophical population ethics. Despite the inherent challenges of these questions, this literature has produced theoretical insights and subsequent progress on variable-population welfare criteria. A surprisingly bounded set of coherent alternatives exists for practitioners once a set of uncontroversial axioms is adopted from the better-studied welfare criteria for cases where populations are assumed to be fixed. Although consensus has not yet been reached among these remaining alternatives, their recommendations often agree. The space has been sufficiently restricted and well explored that applications of the theoretical insights are possible and underway in earnest.
If non-human animals experience wellbeing and suffering, such welfare consequences arguably shoul... more If non-human animals experience wellbeing and suffering, such welfare consequences arguably should be included in a social welfare evaluation. Yet economic evaluations almost universally ignore non-human animals, in part because axiomatic social choice theory has failed to propose and characterize multi-species social welfare functions. Here we propose axioms and functional forms to fill this gap. We provide a range of alternative representations, characterizing a broad range of possibilities for multi-species social welfare. Among these, we identify a new characterization of additively-separable generalized (multi-species) total utilitarianism. The multispecies setting permits a novel, weak species-level separability axiom with important consequences. We provide examples to illustrate that non-separability across species is implausible in a multi-species setting, in part because good lives for different species are at very different welfare levels. Finally, we explore the consequences for evaluating climate policy and understanding speciesism and non-climate environmental goals, such as biodiversity.
At first glance, it may seem that climate policy based on estimates of the social cost of carbon ... more At first glance, it may seem that climate policy based on estimates of the social cost of carbon (SCC) presupposes a set of controversial assumptions, especially about what detailed knowledge regulators have about the impacts of climate change, and what the proper role of government and policy is in responding to those impacts. However, I explain why the SCC-based approach need not actually have these problematic presuppositions as well as why SCC estimates may provide the best guide to climate policy when implemented in a way that incorporates a healthy dose of humility. The SCC-based approach can be used in a way that is ecumenical between the wide range of reasonable but incompatible views about the proper goals of government and policy, ranging from views that aim only at market-efficiency, to utilitarian views, to rights-based and other deontological views, to libertarian views, to virtue ethics views, and others. Beyond this, I suggest that the SCC-based approach can help us find an overlapping consensus on a particular climate policy given the range of reasonable but incompatible normative views endorsed in diverse societies. Finally, I consider a number of specific objections to the SCC-based approach that are especially prominent in contemporary discourse and policy debates. I suggest that even if we agree that all of these objections to existing SCC-based analyses have an important kernel of truth, nonetheless the correct response to climate change still involves substantial emissions reductions to be achieved via policy, and the best methods for deciding the magnitude of those reductions still depend essentially on the SCC-based approach.
We find that if all countries adopt the necessary uniform global carbon tax and then return the r... more We find that if all countries adopt the necessary uniform global carbon tax and then return the revenues to their citizens on an equal per capita basis, it will be possible to meet a 2 °C target while also increasing wellbeing, reducing inequality and alleviating poverty. These results indicate that it is possible for a society to implement strong climate action without compromising goals for equity and development.
Existing estimates of optimal climate policy ignore the possibility that carbon tax revenues coul... more Existing estimates of optimal climate policy ignore the possibility that carbon tax revenues could be used in a progressive way; model results therefore typically imply that near-term climate action comes at some cost to the poor. Using the Nested Inequalities Climate Economy (NICE) model, we show that an equal per capita refund of carbon tax revenues implies that achieving a 2 °C target can pay large and immediate dividends for improving well-being, reducing inequality and alleviating poverty. In an optimal policy calculation that weighs the benefits against the costs of mitigation, the recommended policy is characterized by aggressive near-term climate action followed by a slower climb towards full decarbonization; this pattern—which is driven by a carbon revenue Laffer curve—prevents runaway warming while also preserving tax revenues for redistribution. Accounting for these dynamics corrects a long-standing bias against strong immediate climate action in the optimal policy literature.
Tools are needed to benchmark carbon emissions and pledges against criteria of equity and fairnes... more Tools are needed to benchmark carbon emissions and pledges against criteria of equity and fairness. However, standard economic approaches, which use a transparent optimization framework, ignore equity. Models that do include equity benchmarks exist, but often use opaque methodologies. Here we propose a utilitarian benchmark computed in a transparent optimization framework, which could usefully inform the equity benchmark debate. Implementing the utilitarian benchmark, which we see as ethically minimal and conceptually parsimonious, in two leading climate–economy models allows for calculation of the optimal allocation of future emissions. We compare this optimum with historical emissions and initial nationally determined contributions. Compared with cost minimization, utilitarian optimization features better outcomes for human development, equity and the climate. Peak temperature is lower under utilitarianism because it reduces the human development cost of global mitigation. Utilitarianism therefore is a promising inclusion to a set of benchmarks for future explorations of climate equity
The Repugnant Conclusion is an implication of some approaches to population ethics. It states, in... more The Repugnant Conclusion is an implication of some approaches to population ethics. It states, in Derek Parfit's original formulation, For any possible population of at least ten billion people, all with a very high quality of life, there must be some much larger imaginable population whose existence, if other things are equal, would be better, even though its members have lives that are barely worth living.
Reducing greenhouse gas emissions has the 'co-benefit' of also reducing air pollution and associa... more Reducing greenhouse gas emissions has the 'co-benefit' of also reducing air pollution and associated impacts on human health. Here, we incorporate health co-benefits into estimates of the optimal climate policy for three different climate policy regimes. The first fully internalizes the climate externality at the global level via a uniform carbon price (the 'cooperative equilibrium'), thus minimizing total mitigation costs. The second connects to the concept of 'common but differentiated responsibilities' where nations coordinate their actions while accounting for different national capabilities considering socioeconomic conditions. The third assumes nations act only in their own self-interest. We find that air quality co-benefits motivate substantially reduced emissions under all three policy regimes, but that some form of global cooperation is required to prevent runaway temperature rise. However, co-benefits do warrant high levels of mitigation in certain regions even in the self-interested case, suggesting that air quality impacts may expand the range of possible policy outcomes whereby global temperatures do not increase unabated.
What are the prospects for using population policy as tool to reduce carbon emissions? In this pa... more What are the prospects for using population policy as tool to reduce carbon emissions? In this paper, we review evidence from population science, in order to inform debates in population ethics that, so far, have largely taken place within the academic philosophy literature. In particular, we ask whether fertility policy is likely to have a large effect on carbon emissions, and therefore on temperature change. Our answer is no. Prospects for a policy of fertility-reduction-as-climate-mitigation are limited by population momentum, a demographic factor that limits possible variation in the size of the population, even if fertility rates change very quickly. In particular, a hypothetical policy that instantaneously changed fertility and mortality rates to replacement levels would nevertheless result in a population of over 9 billion people in 2060. We use a leading climate-economy model to project the consequence of such a hypothetical policy for climate change. As a standalone mitigation policy, such a hypothetical change in the size of the future population-much too large to be implementable by any foreseeable government programme-would reduce peak temperature change only to 6.4°C, relative to 7.1°C under the most likely population path. Therefore, fertility reduction is unlikely to be an adequate core approach to climate mitigation.
The population ethics literature has long focused on attempts to avoid the repugnant conclusion. ... more The population ethics literature has long focused on attempts to avoid the repugnant conclusion. We show that a large set of social orderings that are conventionally understood to escape the repugnant conclusion do not in fact avoid it in all instances. As we demonstrate, prior results depend on formal definitions of the repugnant conclusion that exclude some repugnant cases, for reasons inessential to any "repugnance" (or other meaningful normative properties) of the repugnant conclusion. In particular, the literature traditionally formalizes the repugnant conclusion to exclude cases that include an unaffected sub-population. We relax this normatively irrelevant exclusion, and others. Using several more inclusive formalizations of the repugnant conclusion, we then prove that any plausible social ordering implies some instance of the repugnant conclusion. This understanding-that it is impossible to avoid all instances of the repugnant conclusion-is broader than the traditional understanding in the literature that the repugnant conclusion can only be escaped at unappealing theoretical costs. Therefore, the repugnant conclusion provides no methodological guidance for theory or policy-making, because it does not discriminate among candidate social orderings. So escaping the repugnant conclusion should not be a core goal of the population ethics literature.
Deciding which climate policies to enact, and where and when to enact them, requires weighing the... more Deciding which climate policies to enact, and where and when to enact them, requires weighing their costs against the expected benefits. A key challenge in climate policy is how to value health impacts, which are likely to be large and varied, considering that they will accrue over long time horizons (centuries), will occur throughout the world, and will be distributed unevenly within countries depending in part on socioeconomic status. These features raise a number of important economic and ethical issues including how to value human life in different countries at different levels of development, how to value future people, and how much priority to give the poor and disadvantaged. In this article we review each of these issues, describe different approaches for addressing them in quantitative climate policy analysis, and show how their treatment can dramatically change what should be done about climate change. Finally, we use the social cost of carbon, which reflects the cost of adding carbon emissions to the atmosphere, as an example of how analysis of climate impacts is sensitive to ethical assumptions. We consider $20 a reasonable lower bound for the social cost of carbon, but we show that a much higher value is warranted given a strong concern for equity within and across generations.
Formal arguments have proven that avoiding the Repugnant Conclusion is impossible without rejecti... more Formal arguments have proven that avoiding the Repugnant Conclusion is impossible without rejecting one or more highly plausible population principles. To many, such proofs establish not only a deep challenge for axiology, but also pose an important practical problem of how policymaking can confidently proceed without resolving any of the central questions of population ethics. Here we offer deflationary responses: first to the practical challenge, and then to the more fundamental challenge for axiology. Regarding the practical challenge, we provide an overview of recent literature that explores the implications for public policy of the Repugnant Conclusion and related puzzles within population ethics, and shows that there is more commonality in the implications of different population axiologies than is generally recognized. The upshot is that uncertainty about population ethics presents no important problem for policymaking, and the importance of population ethics to policymaking has been overstated. We then turn to more fundamental issues about axiology, and describe a new series of formal proofs that undermine the idea that any plausible axiology could avoid the Repugnant Conclusion, including those that are assumed to avoid it in the literature. The philosophical upshot is that the Repugnant Conclusion cannot plausibly be avoided, and so it is a mistake to assume as a constraint on a plausible axiology that it must be avoided, as is assumed by most of the literature in population ethics, including by all of the fundamental impossibility theorems.
Choosing a policy response to climate change seems to demand a population axiology. A formal lite... more Choosing a policy response to climate change seems to demand a population axiology. A formal literature involving impossibility theorems has demonstrated that all possible approaches to population axiology have one or more seemingly counterintuitive implications. This leads to the worry that because axiology is so theoretically unresolved as to permit a wide range of reasonable disagreement, our ignorance implies serious practical ignorance about what climate policies to pursue. We offer two deflationary responses to this worry. First, it may be that given the actual facts of climate change, all axiologies agree on a particular policy response. In this case, there would be a clear dominance conclusion, and the puzzles of axiology would be practically irrelevant (albeit still theoretically challenging). Second, despite the impossibility results, we prove the possibility of axiologies that satisfy bounded versions of all of the desiderata from the population axiology literature, which may be all that is needed for policy evaluation.
The spectre of the repugnant conclusion and the search for a population axiology that avoids it h... more The spectre of the repugnant conclusion and the search for a population axiology that avoids it has endured as a focus of population ethics. This is in part because the repugnant conclusion is often interpreted as a defining problem for totalism, while the implications of averagism and related views are taken to illustrate the theoretical cost of avoiding the repugnant conclusion. However, we show that this interpretation cannot be sustained unless one focuses only on a special case of the repugnant conclusion: namely, the subset of instances of the repugnant conclusion where there is no portion of the population unaffected by the choice between population outcomes (as in Derek Parfit’s original illustration). To avoid an inappropriate focus on only this proper subset of instances of the repugnant conclusion, we formulate a general characterization of the repugnant conclusion. We then prove formally that all leading welfarist axiologies imply this conclusion, including averagism and Ng’s Theory X0 , including probabilistic and ‘very repugnant’ variants that involve the addition of negative lives. We then prove that the full range of axiologies considered by population ethics each imply an extended version of the repugnant conclusion, including axiologies that are incomplete, intransitive, rank-dependent, person-affecting, and/or pluralist. The upshot is that the repugnant conclusion does not ultimately tell against any approach to axiology, and the methodological requirement to avoid the repugnant conclusion should be dropped from population axiology.
The focus of this chapter is public policy and consequentialism, especially issues that arise in ... more The focus of this chapter is public policy and consequentialism, especially issues that arise in connection with the environment – i.e. the natural world, including non-human animals. We integrate some of the existing literature on environmental economics, welfare economics, and policy with the literature on environmental values and philosophy. The emphasis on environmental policy is motivated by the fact that it is arguably the most philosophically interesting and challenging application of consequentialism to policy, as it includes all the challenges of valuing the distribution of human wealth and power, and has the further challenge of putting these consequences on the same scale as consequences for human health, non-human animals, and nature. We suggest that standard methods of (economic) policy analysis provide a good approximation of correct welfarist analysis, except that they must be supplemented with methods for valuing animal wellbeing and tradeoffs with human wellbeing. We then provide the needed methods.
In this chapter, Mark Budolfson and Dean Spears analyse the marginal effect of philanthropic dona... more In this chapter, Mark Budolfson and Dean Spears analyse the marginal effect of philanthropic donations. The core of their analysis is the observation that marginal good done per dollar donated is a product (in the mathematical sense) of several factors: change in good done per change in activity level of the charity in question, change in activity per change in the charity’s budget size, and change in budget size per change in the individual’s donation to the charity in question. They then discuss the “hidden zero problem” that some of the terms in the equation (in particular, the last term) might be “hidden zeros” that prevent donations from doing any good—or worse, imply that they do harm—even if the charity is at the top of effective altruism rankings based on the other factors.
The health co-benefits of CO2 mitigation can provide a strong incentive for climate policy throug... more The health co-benefits of CO2 mitigation can provide a strong incentive for climate policy through reductions in air pollutant emissions that occur when targeting shared sources. However, reducing air pollutant emissions may also have an important co-harm, as the aerosols they form produce net cooling overall. Nevertheless, aerosol impacts have not been fully incorporated into cost-benefit modeling that estimates how much the world should optimally mitigate. Here we find that when both co-benefits and co-harms are taken fully into account, optimal climate policy results in immediate net benefits globally, overturning previous findings from cost-benefit models that omit these effects. The global health benefits from climate policy could reach trillions of dollars annually, but will importantly depend on the air quality policies that nations adopt independently of climate change. Depending on how society values better health, economically optimal levels of mitigation may be consistent with a target of 2 °C or lower.
Proceedings of the National Academy of Sciences, 2017
Future population growth is uncertain and matters for climate policy: higher growth entails more ... more Future population growth is uncertain and matters for climate policy: higher growth entails more emissions and means more people will be vulnerable to climate-related impacts. We show that how future population is valued importantly determines mitigation decisions. Using the Dynamic Integrated Climate-Economy model, we explore two approaches to valuing population: a discounted version of total utilitarianism (TU), which considers total wellbeing and is standard in social cost of carbon dioxide (SCC) models, and of average utilitarianism (AU), which ignores population size and sums only each time period’s discounted average wellbeing. Under both approaches, as population increases the SCC increases, but optimal peak temperature decreases. The effect is larger under TU, because it responds to the fact that a larger population means climate change hurts more people: for example, in 2025, assuming the United Nations (UN)-high rather than UN-low population scenario entails an increase in the SCC of 85% under TU vs. 5% under AU. The difference in the SCC between the two population scenarios under TU is comparable to commonly debated decisions regarding time discounting. Additionally, we estimate the avoided mitigation costs implied by plausible reductions in population growth, finding that large near-term savings ($billions annually) occur under TU; savings under AU emerge in the more distant future. These savings are larger than spending shortfalls for human development policies that may lower fertility. Finally, we show that whether lowering population growth entails overall improvements in wellbeing—rather than merely cost savings—again depends on the ethical approach to valuing population.
Climate change is poised to threaten, disrupt, and transform human life, and the social, economic... more Climate change is poised to threaten, disrupt, and transform human life, and the social, economic, and political institutions that structure it. In light of this, understanding climate change, and discussing how to address it, should be at the very center of our public conversation. Philosophy can make an enormous contribution to that conversation, but only if both philosophers and non-philosophers understand what it can contribute. The sixteen original articles collected in this volume both illustrate the diverse ways that philosophy can contribute to this conversation, and ways in which thinking about climate change can help to illuminate a range of topics of independent interest to philosophers.
The handbook is a partial survey of multiple areas of food ethics: conventional agriculture and a... more The handbook is a partial survey of multiple areas of food ethics: conventional agriculture and alternatives to it; animals; consumption ethics; food justice; food workers; food politics and policy; gender, body image, and healthy eating; and, food, culture and identity. Food ethics, as an academic pursuit, is vast, incorporating work from philosophy as well as anthropology, economics, environmental sciences and other natural sciences, geography, law, and sociology. This Handbook provides a sample of recent philosophical work in food ethics. This philosophical work addresses ethical issues with agricultural production, the structure of the global food system, the ethics of personal food consumption, the ethics of food policy, and cultural understandings of food and eating, among other issues. The work in this Handbook draws on multiple literatures within philosophy, including practical ethics, normative ethics, and political philosophy, as well as drawing on non-philosophical work. Part I considers ethical issues concerning the industrial model of farming that dominates in developed countries, looking most closely at industrial crop farming and its environmental effects. Part II concerns the ethics of animal agriculture. Part III concerns the ethics of consumption: is it morally permissible to consume various products? Part IV concerns justice—including racial, social, and economic justice—in the food system. Part V discusses some ethical and legal issues with specific kinds of food policies, including healthy eating policies, food labeling, and agricultural guest worker programs. Part VI includes four essays taking a critical eye to our public discourse about, and personal experiences of, dieting, healthy eating, and obesity prevention. Lastly, the essays in Part VII concern the personal, social, and moral significance of food.
Food, Ethics, and Society: An Introductory Text with Readings presents seventy-three readings tha... more Food, Ethics, and Society: An Introductory Text with Readings presents seventy-three readings that address real-world ethical issues at the forefront of the food ethics debate. Topics covered include hunger, food justice, consumer ethics, food and identity, food and religion, raising plants and animals, food workers, overconsumption, obesity, and paternalism. The selections are enhanced by chapter and reading introductions, study questions, and suggestions for further reading. Ideal for both introductory and interdisciplinary courses, Food, Ethics, and Society explains basic philosophical concepts for new students and forges new ground on several ethical debates.
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