Simultaneous stabilization of global temperature and precipitation through cocktail geoengineering

Abstract

Solar geoengineering has been proposed as a backup plan to offset some aspects of anthropogenic climate change if timely CO2 emission reductions fail to materialize. Modeling studies have shown that there are trade‐offs between changes in temperature and hydrological cycle in response to solar geoengineering. Here we investigate the possibility of stabilizing both global mean temperature and precipitation simultaneously by combining two geoengineering approaches: stratospheric sulfate aerosol increase (SAI) that deflects sunlight to space and cirrus cloud thinning (CCT) that enables more longwave radiation to escape to space. Using the slab ocean configuration of National Center for Atmospheric Research Community Earth System Model, we simulate SAI by uniformly adding sulfate aerosol in the upper stratosphere and CCT by uniformly increasing cirrus cloud ice particle falling speed. Under an idealized warming scenario of abrupt quadrupling of atmospheric CO2, we show that by combining appropriate amounts of SAI and CCT geoengineering, global mean (or land mean) temperature and precipitation can be restored simultaneously to preindustrial levels. However, compared to SAI, cocktail geoengineering by mixing SAI and CCT does not markedly improve the overall similarity between geoengineered climate and preindustrial climate on regional scales. Some optimal spatially nonuniform mixture of SAI with CCT might have the potential to better mitigate climate change at both the global and regional scales.

Quantifying and Comparing Effects of Climate Engineering Methods on the Earth System

“…A logical next step is therefore to study portfolio scenarios that combine different CE methods and allow investigating potential interactions of the methods. Cao et al () study the simultaneous deployment of different SRM methods, but a combination of land‐, ocean‐ and atmosphere‐based CE is still missing.…”

Global streamflow and flood response to stratospheric aerosol geoengineering

“…Amazon Basin drying is complicated by various factors that are dependent on solar geoengineering. These include (i) the reduced seasonal movement of the ITCZ under solar geoengineering (Smyth et al, 2017;Guo et al, 2018); (ii) changes in sea surface temperature reflecting changes in frequency of El Niño-Southern Oscillation (Harris et al, 2008;Jiménez-Muñoz et al, 2016), although there is no evidence of such changes occurring under SRM (Gabriel and Robock, 2015); and (iii) changes to carbon cycle feedbacks (Chadwick et al, 2017;Halladay and Good, 2017), which would certainly be affected by changes in diffuse radiation under SRM (Bala et al, 2008;Muri et al, 2018).…”

Uncertainty and the basis for confidence in solar geoengineering research

“…Other trade-offs need to be further understood; even though sea level would continue to rise if global mean temperature change was arrested by solar geoengineering 62 , conclusions about the amount of resulting sea level rise should be revisited 63 . There is still substantial uncertainty in the range of climate features that can be effectively managed with SAG 38 and whether that space can be expanded by complementing SAG with, for example, marine cloud brightening or cirrus thinning 64,65 . In the absence of complete knowledge, the climate community has adopted proxies that encapsulate many different climate objectives, typified by the 1.5 °C or 2 °C warming targets to prevent dangerous anthropogenic interference in the climate system 66 .…”