| 英文摘要: | Cost–benefit analysis and risk assessment approaches inform global climate change mitigation policy-making processes. Now, a development in the former shows that optimal carbon tax levels have previously been underestimated by a factor of two. Typically, cost–benefit analysis (CBA) has suggested 'optimal' carbon tax regimes that result in a global temperature rise of around 3 °C, or even eventually (post-2100) 4 °C, above pre-industrial levels. However, risk analysis approaches indicate that these levels of temperature rise result in climate change impacts that pose a high or very high level of risk to society and ecosystems1 (Fig. 1). Thus, the risk analysis approach has generally indicated that higher levels of climate change mitigation are needed, for example, to constrain global mean temperature rise to around 2 °C above pre-industrial. A particularly controversial aspect of CBA is the representation of consumer preferences relating to the future. These assumptions are the strongest drivers of CBA outcomes. Writing in Nature Climate Change, Benjamin Crost and Christian Traeger2 describe an improved approach to determining consumer preferences in CBA — called Epstein-Zin utility — that leads to a lower level of optimal climate change (that is, the level of climate change achieved through carbon taxes set at an 'optimal' level through which economic resources are distributed in a way that maximizes welfare) and results in a temperature increase of approximately 2 °C by 2100, bringing the implications of CBA closer to those of risk assessment.
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