Temperature fluctuations during the Common Era in subtropical southwestern China inferred from brGDGTs in a remote alpine lake

Documenting climate change over the past 2000 years, or the Common Era, is critical to understand how the climate system evolved from one controlled by natural forcings alone to one influenced by anthropogenic greenhouse gas forcing. However, global and regional temperature changes during this interval are still poorly understood, largely due to the limited geographical coverage and scarcity of data. Here we report a well-dated, quantitative, mean annual air temperature (MAAT) record with ∼10-yr resolution for the Common Era derived from a sediment core collected at a small alpine lake in remote subtropical southwestern China, and based on a site-specific temporal calibration between down-core analyses of brGDGTs and instrumental data for the interval 1959–2015 AD. The record reveals distinct multicentennial-scale temperature fluctuations, including a relatively cold interval from 0–800 AD, followed by warmer temperatures during the so-called Medieval Climate Anomaly (MCA; 800–1400 AD), cooling during the Little Ice Age (LIA; 1400–1900 AD), and abrupt and rapid warming into the late-20th-century after 1900 AD. Superimposed on these large-scale features are three short-term cold events, centered on 250–310 AD (∼0.06 °C), 570–650 AD (∼0.87 °C), and 1800–1823 AD (∼0.83 °C), respectively. The temperature variations captured in the record are supported by historical documents and existing regional and global paleoclimate records, and correspond in time to a number of the major Chinese dynastic transitions. Importantly, the record captures large-magnitude (up to 4 °C) centennial-scale temperature fluctuations, documents cold conditions during the first millennium AD, and demonstrates that the post-1989 AD warmth is greater than any other time during the past 2000 years. The results suggest that high-elevation areas have been more sensitive than low-elevation regions to climate variations during the Common Era.