Seasonal imprint of Holocene temperature reconstruction on the Tibetan Plateau

The Tibetan Plateau (TP) is one of the most sensitive areas to global climate changes. Quantitative paleotemperature reconstructions on the TP since the Last Deglaciation provide a prominent opportunity not only for assessing the position, but also for better understanding the mechanism of recent warming. In this study, we first present a well-dated, high-resolution (~70 years), ice-free-season temperature (from March to October, TM-O) record over the past 19 ka from a small alpine lake on the southeastern TP based on brGDGT proxy. Our reconstructed TM-O record displays a long-term ~4 °C warming trend during the past 19 ka with a deglacial increase of ~3 °C and Holocene increase of ~1 °C. To better understand the pattern and mechanism of postglacial temperature changes on the TP, we review 16 published paleotemperature records since the Last Deglaciation. The results show a general warming pattern during the Last Deglaciation but divergent trends of seasonal temperatures during the Holocene with a gradual cooling pattern in summer temperature, an overall warming pattern in winter temperature, annual temperature, and TM-O as well as a warming-cooling-warming pattern in TMJJAS (temperature from May to September). Data-model comparison indicates that the long-term warming trend in deglacial temperatures are primarily driven by rising atmospheric greenhouse gases (GHGs) on the TP. In contrast, Holocene temperature changes are mainly controlled by local seasonal insolation and additional radiative forcing of GHGs on the TP, thereby resulting in divergent patterns of seasonal temperature changes. Our study highlights the necessity of taking into account the seasonal bias when reconstructing temperatures, especially in high latitudes and high altitudes where the freezing occurs.