Policymakers, scientists, and social scientists have debated a wide array of responses to the realities and prospects of anthropogenic climate change. The focus of this review is on the 2°C temperature target, described as the maximum allowable warming to avoid dangerous anthropogenic interference in the climate. The temperature target has its roots in the ways in which scientists and economists developed heuristics from the 1970s to guide understanding and policy decision making about climate change. It draws from integrated assessment modeling, the ‘traffic light’ system of managing climate risks and a policy response guided as much by considerations of tolerability of different degrees of climate change as by simply reducing carbon dioxide emissions. The European Union (EU) proposed 2°C as the policy target in 1996, with support from some environmentalists and scientists. It was subsequently listed as the desirable temperature target in the 2009 Copenhagen Accord. Yet the figure has a range of critics from scientific experts to economists arguing that the target is infeasible, expensive, and an inappropriate way of framing climate policy. Tracing the historical development of the target helps understand the context it emerged from and its various strengths and weaknesses. © 2010 John Wiley & Sons, Ltd.

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