Integrated Assessment for Setting Greenhouse Gas Emission Targets under the Condition of Great Uncertainty about the Probability and Impact of Abrupt Climate Change

In this paper the mid-21st-century target level for industrial carbon dioxide emissions is analyzed, taking into account the very large uncertainty about abrupt climate change. Following a brief review of integrated assessments of abrupt climate change, this study introduces an extension of DICE-2007, an integrated assessment model for climate policy analysis, which contains a hazard function that connects the rise in air temperature with the probability of abrupt change. The probability of abrupt change under a certain air temperature conditions and the economic impact of abrupt change are treated as widely variable parameters. Graphic indications of the combination of these parameters for several emission targets using the extended model show the necessity of developing adaptation measures to control the economic loss from abrupt change to below 8%, as well as to restrain global industrial carbon emissions in 2055 to the same level as those in 2005, assuming a most likely equilibrium climate sensitivity of 3 oC. Although a more stringent emissions target may be suggested in the spirit of precaution, it may lead to excessive carbon reduction from the viewpoint of cost-benefit balancing.