Evaluation of historical CMIP6 model simulations and future projections of temperature over the Pan-Third Pole region

Environmental Science and Pollution Research https://doi.org/10.1007/s11356-021-17474-7 RESEARCH ARTICLE Evaluation of historical CMIP6 model simulations and future projections of temperature over the Pan‑Third Pole region Xuewei Fan1 · Qingyun Duan1,2 · Chenwei Shen1 · Yi Wu1 · Chang Xing1 Received: 17 June 2021 / Accepted: 8 November 2021 © The Author(s) 2021 Abstract The Pan-Third Pole (PTP) region, which encompasses the Eurasian highlands and their surroundings, has experienced unprecedented, accelerated warming during the past decades. This study evaluates the performance of historical simulation runs of the Coupled Model Intercomparison Project (CMIP6) in capturing spatial patterns and temporal variations observed over the PTP region for mean and extreme temperatures. In addition, projected changes in temperatures under four Shared Socioeconomic Pathway (SSP) scenarios (SSP1‐2.6, SSP2‐4.5, SSP3-7.0, and SSP5‐8.5) are also reported. Four indices were used to characterize changes in temperature extremes: the annual maximum value of daily maximum temperature (TXx), the annual minimum value of daily minimum temperature (TNn), and indices for the percentage of warm days (TX90p) and warm nights (TN90p). Results indicate that most CMIP6 models generally capture the characteristics of the observed mean and extreme temperatures over the PTP region, but there still are slight cold biases in the Tibetan Plateau. Future changes of mean and extreme temperatures demonstrate that a strong increase will occur for the entire PTP region during the twentyfirst century under all four SSP scenarios. Between 2015 and 2099, ensemble area-averaged annual mean temperatures are projected to increase by 1.24 °C/100 year, 3.28 °C/100 year, 5.57 °C/100 year, and 7.40 °C/100 year for the SSP1-2.6, SSP24.5, SSP3-7.0, and SSP5-8.5 scenarios, respectively. For TXx and TNn, the most intense warming is projected in Central Asia. The greatest number of projected TX90p and TN90p will occur in the Southeast Asia and Tibetan Plateau, respectively. Keywords CMIP6 · Temperature · The Pan-Third Pole · Climate change Introduction Responsible Editor: Marcus Schulz Highlights • CMIP6 models perform well in reproducing the spatial and temporal variability of the mean and extreme temperatures over the PTP region. • The performance of the multi-model mean is superior to that of most individual models. • CMIP6 models reported a strong increase in mean and extreme temperatures over the PTP region during the twenty-first century. * Qingyun Duan 1 State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China 2 College of Hydrology and Water Resources, Hohai University, Nanjing 210098, China Warming of the climate system is unequivocal, a fact that has drawn overwhelming attention from the public, governments, and academic communities in recent decades (Gou et al. 2021). The warming has exerted profound, worldwide impacts on human life (Cheng et al. 2018; Sun et al. 2019), agricultural production (Liu et al. 2019, 2021; Tigchelaar et al. 2018), land use (Seneviratne et al. 2018), and natural ecosystems (Gou et al. 2020; Zheng et al. 2021). Among the areas expected to be sensitive to this warming is the region known as the Third Pole, which includes the Tibetan Plateau and the mountains surrounding it. Extending westward and northward from the Third Pole, the Pan-Third Pole (PTP) region is the core region of the “The Belt and Road” initiative promoted by the Chinese government, which has been building a new platform for international cooperation among more than 70 countries in Asia, Africa, and Europe. It covers more than 20 million km2 and supports over 3 billion people 13 Vol.:(0123456789) Environmental Science and Pollution Research with its resources. The PTP region is among the regions in the world most vulnerable to the impact of climate change, since it has the world’s highest elevations and hosts the largest mass of glaciers and snow cover outside the polar regions (Wang et al. 2020). Under global warming, the PTP region, and especially the Tibetan Plateau, has experienced rates of warming twice the global average over the last 50–60 years (Deng et al. 2017; Pepin et al. 2019; You et al. 2019). Furthermore, the projected warming of some areas of the PTP region will exceed 4 °C above pre-industrial levels by 2100, which far exceeds the 2 °C goal set by the Paris Agreement of the United Nations Framework Convention on Climate Change (Yao et al. 2017). The warming in the PTP region is causing Earth system changes characterized by intensive interactions among the processes of the atmosphere, hydrosphere, cryosphere, and biosphere, and is resulting in environmental threats such as glacier retreat, ice collapse, glacial lake expansion, and frequent glacier lake outburst flood (Miao et al. 2021; Yang et al. 2014; Yao et al. 2019). These changes may have impacts on the regional and global hydrologic cycle, thereby hindering socioeconomic development in countries along the routes of the Belt and Road Initiative. A deeper understanding of climate changes in the PTP region can inform science-based adaptation strategies to reduce climate risks. Global climate models (GCMs) have become a major and vital tool for projecting future changes in climate; their reliability depends on their ability to reproduce historical and current climate features. To this end, the World Climate Research Programme has promoted a set of experiments known as the Coupled Model Intercomparison Project (CMIP) since the 1990s, which have delivered systematic and high-quality simulations for better understanding past climate changes and making projections and uncertainty estimates of the future (Annan and Hargreaves 2011; Meehl et al. 2000). Studies using simulations from the fifth phase of CMIP (CMIP5; Taylor et al. 2012) have advanced our understanding of regionally heterogeneous climate warming (Bannister et al. 2017; Ongoma et al. 2018; Sun et al. 2017, 2020), highlighting strong warming trends in the high latitudes of the Northern Hemisphere and moderate warming trends in the middle latitudes (Feng et al. 2014). Several studies have investigated the performance of CMIP models for the PTP region. For example, Dong et al. (2018) assessed the performance of CMIP5 historical simulations and projected future changes under three Representative Concentration Pathways (RCP2.6, RCP4.5, and RCP8.5) over critical Belt and Road regions based on data from 22 models. They found the most significant areas of warming are expected in Kazakhstan and the northern part of the south Belt and Road region. Kamworapan and Surussavadee (2019) evaluated the performances of forty 13 CMIP5 models for simulating climatological temperature and precipitation for Southeast Asia and suggest the use of an ensemble they called 6-GCM-Ensemble for climate studies and projec (...truncated)