Regional differences in the timing of recent air warming during the past four decades in China

Global surface temperature has dramatically increased in the past decades. It is critical to evaluate such a change using appropriate approaches. The previous studies for assessment of the change usually used overall trends of temperature series (i.e. slopes of simple linear regression of temperature versus year based on a least-square analysis) for entire study period. Temperature trends, however, differ among different periods, i.e. there are often breakpoints in the temperature series. Therefore, the overall linear trend of a temperature series may conceal some of the temporal characteristics of the temperature change. To precisely characterize the temporal and spatial patterns of air temperature change in China, we analyze the annual mean temperature series between the year of 1961-2004 for 536 meteorological stations across China, using piecewise linear regression approach. We found remarkable breakpoints in the annual mean temperature during the study period across the country. The annual mean temperature started to increase in 1984 at a rate of 0.058A degrees C/a at the country level. The year when warming started appeared to be gradually later from the north to the south: temperature increased since the 1970s in the north (north of 40A degrees N), and did not rise until the 1980s in most areas of the south (south of 40A degrees N), with warming starting in 1983 in the Tibetan Plateau. The trends in annual mean temperatures showed a large spatial heterogeneity across China: a relatively small rising with a rate of 0.025-0.05A degrees C/a in the Sichuan Basin, Central China and South China; the greatest increase in some parts of northwest China (i.e. Xinjiang) with up to a rate of 0.1A degrees C/a; and rising at a rate of > 0.05A degrees C/a for most regions of the country. The feedbacks of cold waves and snow may be responsible for such regional differences in the timing and rates of warming in China.