Catastrophic climate change, population ethics and intergenerational equity
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Catastrophic climate change, population ethics and intergenerational equity 1 ´ Mejean ´ Aurelie
´ · Antonin Pottier2 · Marc Fleurbaey3 · Stephane Zuber3
Received: 29 December 2019 / Accepted: 13 October 2020 / © Springer Nature B.V. 2020
Abstract Climate change threatens irreversible and dangerous impacts, possibly leading to extinction. The most relevant trade-off then may not be between present and future consumption but between present consumption and the mere existence of future generations. To investigate this trade-off, we build an integrated assessment model that explicitly accounts for the risk of extinction of future generations. Using the class of number-dampened utilitarian social welfare functions, we compare different climate policies that change the probability of catastrophic outcomes yielding an early extinction. We analyse the role of inequality aversion and population ethics. Low inequality aversion and a preference for large populations favour the most ambitious climate policy, although there are cases where the effect of inequality aversion on the preferred policy is reversed. This is due to the fact that a higher inequality aversion both decreases the welfare loss of reducing consumption of the current generation and also decreases the welfare gain of reducing the future risk of extinction. Keywords Climate change · Catastrophic risk · Equity · Population · Climate-economy model
1 Introduction The risk of abrupt and irreversible changes to the climate is one of the five reasons for concern identified by the IPCC (McCarthy et al. 2001; Field et al. 2014). Such abrupt changes are generally associated with tipping points (Lenton et al. 2008), like the shutoff of the Atlantic thermohaline circulation, the collapse of the West Antarctic ice sheet or the dieback
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10584-020-02899-9) contains supplementary material, which is available to authorized users. Aur´elie M´ejean
[email protected] 1
CIRED (CNRS), 45 bis avenue de la Belle Gabrielle, 94736, Nogent-sur-Marne C´edex, France
2
CIRED (EHESS), Nogent-sur-Marne, France
3
Paris School of Economics (CNRS), Paris, France
Climatic Change
of the Amazon rainforest. They may have indirect impacts, for instance through increased migration and conflicts (Reuveny 2007; Hsiang et al. 2013). Catastrophic outcomes can also arise from discontinuities in the response of socio-economic systems to climate change. What is the impact of climate change catastrophes on climate policy making? In this paper, we study a specific instance of such a climate change catastrophe, namely human extinction. There is evidence that climate change may bring about a global catastrophe. One reason is that the level of warming itself is very uncertain and may be much larger than expected. Wagner and Weitzman (2015) have produced estimates of possible extreme temperature rises in a medium-high emission pathway. They estimate the probability of eventual warming of 6 ◦ C to be
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