Attribution and Projection of Winter Extreme Cold Events and Temperature Changes over China

This study synthesizes two related research efforts to investigate the spatiotemporal characteristics, driving mechanisms, attribution, and future projections of winter extreme cold events and annual mean temperature changes over China since 1961. For extreme cold events, three indices are analyzed, including the intensity of cold extremes (TNn), frost days (FD), and ice days (ID), based on station observations, CMIP6 model simulations, and large-scale circulation indices. Results show an overall weakening of winter cold extremes across China, accompanied by pronounced regional and interdecadal variations. The decreasing trends tend to slow down in eastern China, while extreme cold events have intensified in Northeast China since the 1990s. In western China, cold extremes continue to weaken but at a reduced rate. Anthropogenic forcing is identified as the dominant driver of the weakening of extreme cold events in eastern China, whereas the negative phase of the Arctic Oscillation (AO) and the strengthening of the Siberian High significantly enhance cold extremes. In addition, Arctic amplification and the associated weakening of the polar vortex contribute to increased southward outbreaks of cold air.

For annual mean temperature, detection and attribution analyses are conducted using CMIP5 and CMIP6 model simulations based on the optimal fingerprinting method, combined with an observation-constrained approach to reduce model biases. The results demonstrate that anthropogenic forcing is the primary contributor to the observed warming over China, while some CMIP6 models tend to overestimate the warming magnitude. After applying attribution constraints, projected warming under high-emission scenarios (2081–2100) is substantially reduced compared to unconstrained projections, leading to improved consistency between CMIP5 and CMIP6 results and a significant reduction in uncertainty.

Despite the overall decrease in the risk of extreme cold events under global warming, internal climate variability associated with large-scale circulation continues to modulate regional cold extremes. These findings highlight the importance of considering the interplay between long-term warming trends and interdecadal variability, and emphasize the need to improve regional climate simulations to better support climate adaptation and disaster risk reduction strategies.