Does elevation-dependent warming hold true above 5000 m elevation? Lessons from the Tibetan Plateau

Abstract

Available observations below 5000 m altitude suggest that some mountain regions are undergoing accelerated elevation-dependent warming (EDW) in response to global or regional climate change. We address the question of whether EDW exists above 5000 m altitude, which is the elevation of much of the mountainous portion of the Tibetan Plateau, and headwaters to most of Asia’s major rivers. We analyzed four data sources: in situ observations, gridded observations, ERA-Interim reanalysis, and Weather Research and Forecasting (WRF) regional climate model output over the portion of the Tibetan Plateau above 5000 m elevation. We also analyzed the relative contributions of changes in water vapor, diabatic heating, snow, and surface energy changes to EDW in WRF simulations and ERA-Interim. Gridded observations over the Tibetan Plateau show EDW below 5000 m, in apparent consistency with studies elsewhere. However, the gridded observations above 5000 m are essentially entirely extrapolated from lower elevations. Despite differences in details, neither ERA-Interim nor WRF indicate EDW above 5000 m. The WRF simulation produces more realistic temperature profiles at elevations where observations exist, which are also consistent with the simulated profiles of factors contributing to vertical heating. Furthermore, WRF projects no EDW above 5000 m in future climate projections (with CCSM4 boundary conditions) for RCP 4.5 and 8.5 global emission scenarios. Therefore, we conclude that EDW above 5000 m over the Tibetan Plateau is not occurring, nor is it likely to occur in future decades.