Responses of the Leading Mode of Coldwave Intensity in China to a Warming Climate

Regional extreme cold events have changed notably with recent global warming. Understanding how these cold extremes change in China is an urgent issue. This study examines the responses of the dominant mode of China coldwave intensity (CWI) to global warming by comparing observations with simulations from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). The leading modes of the CWI derived from empirical orthogonal function (EOF) analysis have different features in different epochs. During the cold period (1957-1979), the leading mode is characterized by centers of extreme values of CWI in northern China; while during the warm period (1980-2009), the leading mode features two maximum loading centers over northern and southern China. The southward extension of the extreme value center is associated with an increase in the intensity of coldwave variations in southern China relative to previous decades. A multi-model ensemble of seven state-of-the-art climate models shows an extension of the maximum loading of the CWI leading mode into southern China by the end of the 21st century (2080-2099) under the A1B global warming scenario (atmospheric CO2 concentration of 720 ppm). These results indicate that the primary response of the leading mode of CWI to global warming might be a southward extension of the extreme value center. This response may be associated with the southward shift of the storm track observed during recent decades. A significant change in the baroclinic growth rates around 40°N is accompanied by a consistent change in synoptic eddies in the troposphere, which may indicate a shift in the preferred latitude for the growth of eddies. As a result, the storm track tends to move southward, suggesting that southern China may experience increased storminess due to increased baroclinic instability in the troposphere.