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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.

Plain Language Summary Increases in atmospheric carbon dioxide cause increase in both global temperatures and precipitation. Solar geoengineering has been proposed as a means to counteract this climate change by deliberately deflecting more sunlight from the Earth's climate system. Numerous climate modeling studies have shown that proposed solar geoengineering schemes, such as injection of sulfate aerosols into the stratosphere, can cool climate, but the amount of precipitation change per degree of temperature change is greater than that for CO2, meaning that such proposals cannot simultaneously globally restore both average temperatures and average precipitation. It has also been suggested that the Earth could be cooled by thinning cirrus clouds, but the amount of precipitation change per degree of temperature change for this method is less than that for CO2. Our climate modeling study shows, for the first time, that a cocktail of these two approaches would decrease precipitation and temperature in the same ratios as they are increased by CO2, which would allow simultaneous recovery of preindustrial temperature and precipitation in a high CO2 world at global scale. We show that although the average temperatures and precipitation can be recovered at global scale, substantial differences between the geoengineered and natural climates persist at regional scale.