Patterns of evaporation and precipitation drive global isotopic changes in atmospheric moisture

Because water isotope ratios respond to phase changes during evaporation (E) and precipitation (P), they are candidate fingerprints of changing atmospheric hydrology. Moreover, through preservation in ice cores and other paleoproxies, they provide important insight into the past. Still, there is disagreement over what specific attributes of hydroclimate variability isotopes reveal. Here we argue that variations in zonal mean isotope ratios of water vapor and precipitation are largely a response to geographically shifting patterns of E and P. Differences in the relative importance of local versus remote changes in these moisture variables explain the apparent distinct isotopic sensitivities to temperature and precipitation amount in high and low latitudes, respectively. Not only does our work provide a unified framework for interpreting water isotopic measurements globally, but it also presents a novel approach for diagnosing water cycle changes in a warmer world.