Rising temperatures and changing dynamics can both moisten the air, making it difficult to disentangle these interrelated drivers of water cycle change. However, work by Camille Risi and colleagues presents a new way to distinguish their effects. Using large-eddy simulations with water isotopic tracers, they show that while warming the sea surface increases the ratio of isotopically heavy-to-light water in the tropical marine subcloud layer, strengthening the moisture flux convergence decreases it. This divergent response provides a new framework for examining the complex mechanisms that regulate the development of convection and, ultimately, cloudiness-a target of the 2020 international field campaign EUREC4A (ElUcidating the RolE of Clouds-Circulation Coupling in ClimAte). Moreover, their findings provide a clearer picture of why water isotopes recorded in tropical paleoproxies are a valuable lens through which to view changes in moisture transport in the past.
