Allowable CO2 emissions based on regional and impact-related climate targets

Global temperature targets, such as the widely accepted limit of an increase above pre-industrial temperatures of two degrees Celsius, may fail to communicate the urgency of reducing carbon dioxide (CO2) emissions. The translation of CO2 emissions into regional- and impact-related climate targets could be more powerful because such targets are more directly aligned with individual national interests. We illustrate this approach using regional changes in extreme temperatures and precipitation. These scale robustly with global temperature across scenarios, and thus with cumulative CO2 emissions. This is particularly relevant for changes in regional extreme temperatures on land, which are much greater than changes in the associated global mean. Targets for reducing atmospheric carbon dioxide are related to regional changes in climate extremes rather than to changes in global mean temperature, in order to convey their urgency better to individual countries. A major theme in the fifth assessment report of the Intergovernmental Panel on Climate Change was that global mean surface temperature scales linearly with cumulative emissions of greenhouse gases. Sonia Seneviratne et al. show that a similar scaling exists between cumulative emissions and regional changes in the occurrence of extremes in precipitation and temperatures. The presentation of targets regionally, rather than globally, has the advantage of conveying their urgency better to individual countries.