Management of trade-offs in geoengineering through optimal choice of non-uniform radiative forcing

Abstract

Solar radiation management could be used to offset some or all anthropogenic radiative forcing, with the goal of reducing some of the associated climatic change. However, the degree of compensation will vary, with residual climate changes larger in some regions than others. Similarly, the insolation reduction that best compensates climate changes in one region may not be the same as for another, leading to concerns about equity. Here we show that optimizing the latitudinal and seasonal distribution of solar reduction can improve the fidelity with which solar radiation management offsets anthropogenic climate change. Using the HadCM3L general circulation model, we explore several trade-offs. First, residual temperature and precipitation changes in the worst-off region can be reduced by 30% relative to uniform solar reduction, with only a modest impact on global root-mean-square changes; this has implications for moderating regional inequalities. Second, the same root-mean-square residual climate changes can be obtained with up to 30% less insolation reduction, implying that it may be possible to reduce solar radiation management side-effects and risks (for example, ozone depletion if stratospheric sulphate aerosols are used). Finally, allowing spatial and temporal variability increases the range of trade-offs to be considered, raising the question of how to weight different objectives.