There now appears to be a plausible pathway for reviving species that have been extinct for several decades, centuries, or even millennia. I conducted an ethical analysis of de-extinction of long extinct species. I assessed several possible ethical considerations in favor of pursuing de-extinction: that it is a matter of justice; that it would reestablish lost value; that it would create new value; and that society needs it as a conservation last resort. I also assessed several possible ethical arguments against pursuing de-extinction: that it is unnatural; that it could cause animal suffering; that it could be ecologically problematic or detrimental to human health; and that it is hubristic. There are reasons in favor of reviving long extinct species, and it can be ethically acceptable to do so. However, the reasons in favor of pursuing de-extinction do not have to do with its usefulness in species conservation; rather, they concern the status of revived species as scientific and technological achievements, and it would be ethically problematic to promote de-extinction as a significant conservation strategy, because it does not prevent species extinctions, does not address the causes of extinction, and could be detrimental to some species conservation efforts. Moreover, humanity does not have a responsibility or obligation to pursue de-extinction of long extinct species, and reviving them does not address any urgent problem. Therefore, legitimate ecological, political, animal welfare, legal, or human health concerns associated with a de-extinction (and reintroduction) must be thoroughly addressed for it to be ethically acceptable.

Environmental ethics-the study of ethical questions raised by human relations with the nonhuman environment-emerged as an important subfield of philosophy during the 1970s. It is now a flourishing area of research. This article provides a review of the secular, Western traditions in the field. It examines both anthropocentric and nonanthropocentric claims about what has value, as well as divergent views about whether environmental ethics should be concerned with bringing about best consequences, respecting principles and rights, or embodying environmental virtues. The article also briefly considers two critical traditions-ecofeminism and environmental pragmatism-and explores some of the difficult environmental ethics questions posed by anthropogenic climate change.

Discourse around assisted colonization focuses on the ecological risks, costs, and uncertainties associated with the practice, as well as on its technical feasibility and alternative approaches to it. Nevertheless, the ethical underpinnings of the case for assisted colonization are claims about the value of species. A complete discussion of assisted colonization needs to include assessment of these claims. For each type of value that species are thought to possess it is necessary to determine whether it is plausible that species possess the type of value and, if so, to what extent their possessing it justifies assisted colonization. I conducted such an assessment for each of the predominant types of value ascribed to species: ecological, instrumental (including option value), existence, and intrinsic value (including interest-based, objective, and valuer-dependent intrinsic value). The vast majority of species, including several that have been proposed as candidates for assisted colonization, have much less value than is often presumed. Moreover, with respect to some types of value, assisted colonization would not fully preserve the value of the target species even if it were to keep the target species in existence. Therefore, the case for assisted colonization is significantly weaker and more qualified than its advocates often suppose. There may be exceptional species for which assisted colonization is well justified--and for this reason, case-by-case assessment is necessary--but in general the burden of justification generated by the ecological risks associated with assisted colonization is not met by the value potentially preserved by assisted colonization. This suggests that assisted colonization ought to have, at most, a very minor role in the portfolio of ecosystem management practices, even as it pertains to species conservation under conditions of rapid climate change.

* Correspondence and requests for materials should be addressed to r.smead@neu.edu. We would like to thank the editors at Nature Climate Change as well as two anonymous reviewers for helpful comments on a previous draft of this manuscript. RLS and RS oversaw the project. RS and PF developed the models and ran simulations. RLS and JB analyzed the status of current climate negotiations and policy. RLS, RS, PF, and JB jointly developed how to apply the model to climate negotiations, derived general recommendations, and wrote the paper.

Environmental ethics ( see Environmental Ethics) is the study of the ethical relationships between human beings and the natural environment, including the nonhuman individuals that populate and constitute it. It involves developing a proper understanding of the human–nature relationship, identifying the goods and values that are part of or emerge from that relationship, determining the norms (rules/principles) that those goods and values justify, and applying those norms to generate guidance on environmental issues and interactions. Environmental virtue ethics is that part of environmental ethics that concerns character ( see Virtue Ethics). The core questions of environmental virtue ethics are these: