Global water cycle amplifying at less than the Clausius-Clapeyron rate

TL;DR

The global water cycle’s shift from dry to wet regions could profoundly affect humanity, yet while air warming increases moisture capacity at ~7 % °C⁻¹ (Clausius–Clapeyron), surface salinity data suggest amplification near this rate, conflicting with climate model predictions. The study aims to infer changes in the global water cycle from three‑dimensional salinity variations using water‑mass transformation theory. The authors apply water‑mass transformation theory to full‑depth salinity observations to estimate water‑cycle amplification. They find a water‑cycle amplification of 3.0 ± 1.6 % °C⁻¹.

Abstract

Abstract A change in the cycle of water from dry to wet regions of the globe would have far reaching impact on humanity. As air warms, its capacity to hold water increases at the Clausius-Clapeyron rate (CC, approximately 7% °C −1 ). Surface ocean salinity observations have suggested the water cycle has amplified at close to CC following recent global warming, a result that was found to be at odds with state-of the art climate models. Here we employ a method based on water mass transformation theory for inferring changes in the water cycle from changes in three-dimensional salinity. Using full depth salinity observations we infer a water cycle amplification of 3.0 ± 1.6% °C −1 over 1950–2010. Climate models agree with observations in terms of a water cycle amplification (4.3 ± 2.0% °C −1 ) substantially less than CC adding confidence to projections of total water cycle change under greenhouse gas emission scenarios.