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How population growth relates to climate change

  1. Wolfgang Lutza,1
  1. aWittgenstein Centre for Demography and Global Human Capital (International Institute for Applied Systems Analysis, Vienna Institute of Demography/Austrian Academy of Sciences, Vienna University of Economics and Business Administration), International Institute for Applied Systems Analysis, Laxenburg, Lower Austria 2361, Austria

Currently, around 7.5 billion people live on our planet and scenarios for the future show a plausible range from 8.5 to over 12 billion before the population will level off or start to decline, depending on the future course of fertility and mortality (1, 2). These people will also have to cope with the consequences of climate change that may be in the range of 1.5 °C to more than 3 °C, depending on the scale of mitigation efforts. The paper by Scovronick et al. in PNAS on the “Impact of population growth and population ethics on climate change mitigation policy” (3) links these two global megatrends and asks how different population scenarios change the rationale for mitigation policies and vice versa. The paper shows convincingly that the answers depend on a rather abstract philosophical choice: namely, whether the goal is to maximize total utility (TU) or average utility (AU).

The field of population ethics, which deals with this question, is tricky because it is filled with contradictions and unacceptable conclusions, whatever position one takes on the issue. Ever since Bentham, the dominant utilitarian position has been that the overall goal is to maximize the wellbeing of the largest possible number of people. Under this TU view, the average wellbeing of people is multiplied with the number of people. But this would also imply that a world with many more people, who on average have a lower level of wellbeing than today, would be better, if it results in a higher TU. Since this implication is difficult to accept, it has also been labeled the “repugnant conclusion” (4). Much has been written about this unsatisfactory conclusion and many ways of dealing with it have been proposed (5), with a focus on average welfare instead of TU being the most …

?1Email: lutz{at}iiasa.ac.at.

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