Moist Adiabatic Scaling Explains Mean and Fast Upper‐Level Jet Stream Wind Response to Climate Change

Abstract The upper‐level jet stream exhibits a robust increase in strength and shear under climate change. Previous work also noted a fast‐get‐faster response and connected it diagnostically to the Clausius‐Clapeyron relation. Here we derive a moist adiabatic scaling that explains the upper‐level jet stream wind response. Given the daily surface air temperature distribution and assuming a moist adiabatic atmosphere, the upper‐level mean and fast jet stream wind increase by 2%/K and the jet stream shear increases by 4%/K across a climate model hierarchy. The scaling shows the increase of the surface moisture gradient following the Clausius‐Clapeyron relation dominates the response. The scaling connects the increasing surface moisture gradient to the upper‐level temperature gradient thereby reconciling dry and moist perspectives. The results show record‐breaking upper‐level jet stream wind and increased clear‐air turbulence are tied to the Clausius‐Clapeyron relation and are therefore robust and well‐understood consequences of climate change.