Near-linear cost increase to reduce climate-change risk
- aEnvironmental Systems Analysis Group, Wageningen University and Research Centre, P.O. Box 47, 6700 AA Wageningen, The Netherlands;
- bClimate and Global Sustainability Group, Netherlands Environmental Assessment Agency, P.O. Box 303, 3720 AH Bilthoven, The Netherlands; and
- cPotsdam Institute for Climate Impact Research, P.O. Box 60 12 03, 14412 Potsdam, Germany
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Edited by Stephen H. Schneider, Stanford University, Stanford, CA, and approved November 12, 2008 (received for review March 13, 2008)

Abstract
One approach in climate-change policy is to set normative long-term targets first and then infer the implied emissions pathways. An important example of a normative target is to limit the global-mean temperature change to a certain maximum. In general, reported cost estimates for limiting global warming often rise rapidly, even exponentially, as the scale of emission reductions from a reference level increases. This rapid rise may suggest that more ambitious policies may be prohibitively expensive. Here, we propose a probabilistic perspective, focused on the relationship between mitigation costs and the likelihood of achieving a climate target. We investigate the qualitative, functional relationship between the likelihood of achieving a normative target and the costs of climate-change mitigation. In contrast to the example of exponentially rising costs for lowering concentration levels, we show that the mitigation costs rise proportionally to the likelihood of meeting a temperature target, across a range of concentration levels. In economic terms investing in climate mitigation to increase the probability of achieving climate targets yields “constant returns to scale,” because of a counterbalancing rapid rise in the probabilities of meeting a temperature target as concentration is lowered.
Footnotes
- 1To whom correspondence should be addressed. E-mail: michiel.schaeffer{at}wur.nl
Author contributions: M.S. designed research; M.S., M.M., and D.P.v.V. performed research; M.S., T.K., M.M., D.P.v.V., and W.L.H. analyzed data; and M.S., T.K., M.M., D.P.v.V., and W.L.H. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
- © 2008 by The National Academy of Sciences of the USA