Evaluation and projections of surface air temperature over the Tibetan Plateau from CMIP6 and CMIP5: warming trend and uncertainty

This paper compares the historical simulations and future projections of surface air temperature over the Tibetan Plateau of the updated Coupled Model Intercomparison Project phase (CMIP6) and the precedent phase of the project (CMIP5) to quantify differences in the projections under different scenarios. Model evaluation for the historical period (1961-2005) indicates that the multi-model ensemble (MME) mean of CMIP6 outperforms CMIP5 MME in simulating spatial-temporal characteristics of surface air temperature. The temperature changes relative to 1986-2005 are projected in the near-term (2021-2040), mid-term (2041-2060), and long-term (2081-2100) future under Shared Socio-economic Pathway (SSP)2-4.5 and SSP5-8.5 of CMIP6 and Representative Concentration Pathway (RCP)4.5 and RCP8.5 of CMIP5. The projected temperature shows larger increases in the long-term projection compared with the near- and mid-term projection under both SSPs and RCPs. CMIP6 MME projects higher temperature changes and accelerated warming trends relative to CMIP5 MME. Additionally, the projected temperature increases and warming rates show a significant elevation dependency, especially in the long-term projection. The uncertainty for future projections is quantified by the square root of error variance (SREV) method. The results record a clear reduction in the uncertainty of CMIP6 temperature relative to CMIP5 primarily concentrated at the elevation zones of over 5000 m. The analysis of the projected temperature over the Tibetan Plateau is of great significance for policy-makers to make socio-economic adjustments for the future warming. This study is conducive to the credibility of future temperature projections for CMIP6 and enhances our comprehension of the uncertainty of SSP and RCP scenarios.