Recent Progresses in Studies of Regional Temperature Changes in China

A brief summary of some recent major research findings of temperature changes over China is made in this paper. The findings come mainly from studies on observed changes of surface air temperature of the last 55 years, 100 years and 1 000 years, and of free atmospheric temperature of the last 50 years, on attribution of surface air temperature change to anthropogenic forcing, and on effect of rapid urbanization on site temperature records and regional average temperature series. Based on a data set of national basic and reference stations, which have been quality-controlled and adjusted for in-homogeneity dominantly induced by relocation of stations, updated surface air temperature time series of the past 55 years and 100 years are established. The new temperature series show a generally more rapid warming than those obtained before, with the rates of change of annual mean temperature reaching 0.22 ℃/10 a. and 0.08 ℃/10 a respectively for the past 55 year and 100 years. The current warming is more significant in Northeast China, North China, Northwest China and the Tibetan Plateau, and the largest increase in temperature occurs in wintertime and springtime. The warming of the last 55 years is the result of more obvious rising of mean minimum temperature. The same change has happened for the country averaged annual extreme low temperature, while the annual extreme high temperature only experiences an insignificant rise. The frequency of temperature-related extreme events such as cold wave, cool summer, hot days generally tends to decrease or to be unchanged in the country as a whole. It is found, however, that significant effects of urbanization on recorded trends of temperature for single stations as well as for region averaged temperature series exist in a few regions investigated so far. In North China which experiences the most remarkable warming in the country, increase of annual mean temperature induced by urbanization for national basic and reference stations reaches 0.44 ℃ in period of 1961—2000, with an increasing rate of temperature of 0.11 ℃/10 a, accounting for 38% of the total warming rate as recorded by these stations. The effects of urbanization might have remained in the other regional changes in annual mean temperature. Regardless the remarkable warming of the surface, mid-to lower troposphere (850—400 hPa) witnesses no significant change in temperature, with a rate of change of only 0.05 ℃/10 a for the period of 1961—2004, and upper troposphere (300—150 hPa) and lower stratosphere (100—50 hPa) are experiencing a significant decrease in temperature at rates of -0.17 ℃/10a and -0.22 ℃/10 a respectively. A slight decrease in temperature is found for the entire troposphere in the period investigated. However, mid-to lower troposphere temperature is increasing in the past 20 years at a much higher rate than before, and the difference of change between surfaces and mid-to lower troposphere is getting smaller. A preliminary temperature series of the past 1 000 years has been reconstructed mainly based on tree ring data in the west and historical record in the east. It shows the warmth of period corresponding to the Medieval Warm Period (MWP) and the marked coldness of the Little Ice Age last from about 1400 to 1900. The warmth of the MWP, however, seems not so evident in the country as a whole as reported before, though the temperature in the end of 11th century and in the mid 13th century might have been higher than that of any decade of 20th century. It is still premature to answer the question of what cause the observed warming on the surface in China. Some evidence support the claim that it has mainly been induced by the increased concentration of greenhouse gases in atmosphere, but the influences of other factors like solar activities and the low-frequency oscillations of ocean-atmospheric system could not be ruled out at present.