The hydrological cycle response to cirrus cloud thinning

Recent multimodel studies have shown that if one attempts to cancel increasing CO 2 concentrations by reducing absorbed solar radiation, the hydrological cycle will weaken if global temperature is kept unchanged. Using a global climate model, we investigate the hydrological cycle response to “cirrus cloud thinning (CCT),” which is a proposed climate engineering technique that seeks to enhance outgoing longwave radiation. Investigations of the “fast response” in experiments with fixed sea surface temperatures reveal that CCT causes a significant enhancement of the latent heat flux and precipitation. This is due to enhanced radiative cooling of the troposphere, which is opposite to the effect of increased CO 2 concentrations. By combining CCT with CO 2 increase in multidecadal simulations with a slab ocean, we demonstrate a systematic enhancement of the hydrological cycle due to CCT. This leads to enhanced moisture availability in low‐latitude land regions and a strengthening of the Indian monsoon.