After two decades of failure by the international community to respond adequately to the threat of global climate change, discussions of the possibility of geoengineering a cooler climate have recently proliferated. Alongside the considerable optimism that these technologies have generated, there has also been wide acknowledgement of significant ethical concerns. Ethicists, social scientists, and experts in governance have begun the work of addressing these concerns. The plethora of ethical issues raised by geoengineering creates challenges for those who wish to survey them. The issues are here separated out according to the temporal spaces in which they first arise. Some crop up when merely contemplating the prospect of geoengineering. Others appear as research gets underway. Another set of issues attend the actual implementation of the technologies. A further set occurs when planning for the cessation of climate engineering. Two cautions about this organizational schema are in order. First, even if the issues first arise in the temporal spaces identified, they do not stay completely contained within them. A good reason to object to the prospect of geoengineering, for example, will likely remain a good reason to object to its implementation. Second, the ethical concerns intensify or weaken depending on the technology under consideration. The wide range of geoengineering technologies currently being discussed makes it prudent that each technique should be evaluated individually for its ethical merit. WIREs Clim Change 2013, 4:23–37. doi: 10.1002/wcc.198
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