Pre-Industrial (1750-1850 CE) Cold Season Warmth in Northeastern China

Contrary to global warming projections, northern mid-latitude continents have suffered from an increased frequency of unusually cold winters during the last few decades. However, a lack of longer-term cold-season temperature records from mid-latitudes hampers our understanding of the forcing mechanisms of this temperature variability. Here we report a Group 1 alkenone-based high-resolution record of cold-season temperatures extending to the pre-industrial era (since 1700 CE) from Lake Luming in northeastern China. By comparing with the instrumental and historical records in the region, we verify the high efficacy of Group 1 alkenones as recorders of cold-season temperature variability. Our record shows pre-industrial warmth between 1750 and 1850 CE relative to anthropogenic industrial period (since 1850 CE), which is largely driven by variability of the Arctic Oscillation, with a negligible contribution from anthropogenic greenhouse-gas forcing. Our results highlight the importance of internal atmospheric circulation in driving cold-season temperatures in northeastern China. Plain Language Summary Frequent occurrence of extreme cold events in northern mid-latitudes during the last few decades imposes significant social and economic impacts. Past reconstructions of longer-term cold-season temperature variability are of crucial importance for understanding past and future cold anomalies. Here we use a paleothermometer proxy based on Group 1 alkenone lipid biomarkers to reconstruct cold-season temperature variability of the last similar to 300 years from a freshwater lake in northeastern China. Our cold-season reconstruction is confirmed by the instrumental and historical records in the region. We show a relatively warm cold-season climate during the pre-industrial period of 1750-1850 CE relative to the period since the industrial revolution (since 1850 CE). More positive cold-season Arctic Oscillation (AO) conditions, rather than anthropogenic greenhouse-gas forcing, may explain this warmth, which is associated with the AO-induced reduction of cold air outbreaks over northeastern China. Our study suggests that internal atmospheric circulation has played an important role in driving cold-season temperature variability in northeastern China on our study timescales.