Geoengineering as a design problem

Abstract

Abstract. Understanding the climate impacts of solar geoengineering is essential for evaluating its benefits and risks. Most previous simulations have prescribed a particular strategy and evaluated its modeled effects. Here we turn this approach around by first choosing example climate objectives and then designing a strategy to meet those objectives in climate models.There are four essential criteria for designing a strategy: (i) an explicit specification of the objectives, (ii) defining what climate forcing agents to modify so the objectives are met, (iii) a method for managing uncertainties, and (iv) independent verification of the strategy in an evaluation model.We demonstrate this design perspective through two multi-objective examples. First, changes in Arctic temperature and the position of tropical precipitation due to CO 2 increases are offset by adjusting high-latitude insolation in each hemisphere independently. Second, three different latitude-dependent patterns of insolation are modified to offset CO 2 -induced changes in global mean temperature, interhemispheric temperature asymmetry, and the Equator-to-pole temperature gradient. In both examples, the "design" and "evaluation" models are state-of-the-art fully coupled atmosphere-ocean general circulation models.

Effects of Arctic geoengineering on precipitation in the tropical monsoon regions

“…3a; Table 3) and we estimate the climate sensitivity as ~0.86 K/Wm −2 . In agreement with several previous studies (Govindasamy and Caldeira 2000;Govindasamy et al 2003;Kravitz et al 2016), we find that the polar regions warm much more than the global mean: the Arctic region (60°N-90°N) warms by ~6.5 K while the Antarctic region (60°S-90°S) warms by ~5.5 K ( Fig. 3a; Table 3).…”

“…Therefore, unlike Kravitz et al (2016) who design the Antarctic forcing to offset the ITCZ shift due to Arctic geoengineering, we choose Antarctic sulfate forcing to offset the Antarctic warming caused by CO 2 doubling. The Arctic region sulfate loading has been reduced from 11 Mt in ARCTIC to 10 Mt in the POLAR case.…”

“…While it is known that the Antarctic sulfate loading would tend to shift the ITCZ back to its original position (Kravitz et al 2016), we design the POLAR experiment such that the warming in both Arctic and Antarctic are also offset. Therefore, unlike Kravitz et al (2016) who design the Antarctic forcing to offset the ITCZ shift due to Arctic geoengineering, we choose Antarctic sulfate forcing to offset the Antarctic warming caused by CO 2 doubling.…”

“…However, uniform global reduction in incoming solar radiation (Govindasamy and Caldeira 2000;Kalidindi et al 2014;Kravitz et al 2016) can restore global mean temperatures without shifting the ITCZ Kravitz et al 2016) but it could overcool the tropics and leave residual warming in the polar regions (Govindasamy et al 2003). In order to reduce regional anomalies, some studies (Ban-Weiss and Caldeira 2010;MacMartin et al 2013;Modak and Bala 2014;Kravitz et al 2016) imposed a latitudinal distribution of solar insolation reduction or sulfate aerosol prescription such that the temperature and precipitation anomalies in all latitudes were minimized.…”

“…However, when comparable solar reduction is imposed in both NH and SH high latitudes, the position of ITCZ is nearly unaltered. Kravitz et al (2016) showed that annual mean Arctic temperature and ITCZ location can be adjusted by reducing solar radiation in the Arctic and Antarctic by appropriate amounts.…”