Divergent trends of changes in annual mean and summer temperature in southwestern China during the Holocene

Reconstructing Holocene temperature changes in the continental setting is crucial for better assessing the position of recent global warming within the context of long-term natural climate variability and understanding the relationship between temperature changs and monsoon system. However, the pattern and rate of Holocene temperature variations still remain enigmatic due to lack of land-based proxy reconstructions with an unambiguous climatic significance. Here we present a well-dated, high-resolution, quantitative temperature record based on brGDGT proxy during the past 8000 years from the Chenghai Lake in southwestern China. A systematic modern investigation reveals a close correlation between the reconstructed and instrumental mean annual air temperature (MAAT) during the past 60 years, suggesting that sedimentary brGDGT proxy can capture the variations of MAAT during the geological past with a high fidelity. Within an improved chronological framework, our reconstructed Holocene MAAT record displays a long-term warming trend with a magnitude of ∼1.5 °C. This overall warming pattern is consistent with the variations of existing regional MAAT records, but in contradiction to the summer temperature records which is similar to the variation of the Asian summer monsoon. In light of state-of-the-art transient climate simulations, we demonstrate that changes in Holocene MAAT were forced by local annual-mean insolation with an additional radiative forcing of greenhouse gases, while changes in summer temperature were mainly controlled by local summer insolation, thereby resulting in a divergent pattern of seasonal temperature changes in southwestern China. Our study provides new evidence for reconciling the “Holocene temperature conundrum” between proxy reconstruction and model simulations from low latitudes.