Twentieth-century climatic warming in China in the context of the Holocene

Development of an annual mean temperature series of China for the period of AD 1880-1998 indicated that 1998 was the warmest year since 1880. During 1998, temperature was 1.38 degreesC higher than the normal (1961-90). Annual mean temperatures of China were found using a weighted average of 10 regional series, which covered the whole land area of the country from Xinjiang and Tibet in the west to Taiwan in the east. Gaps in temperature observations were filled by using ice-core delta O-18 and tree-ring data for three regions in the west, and documentary data for seven regions in the east. Since 1951, only observational data were used. Fifty-year mean temperature anomalies were calculated from the ninth to twentieth centuries. The series do not show any consistent warm period in west China during the 'Mediaeval Warm Period' (AD 900 to 1300), but temperatures in east China in AD 850-1099 and 1200-99 were about 0.2 degreesC higher than the average for recent years. Century-mean temperatures combining west and east regions from the ninth to twentieth centuries showed that the twentieth century was 0.4 degreesC warmer than the mean of the whole period. Temperatures of the ninth, tenth, eleventh and thirteenth centuries were only slightly (0.05-0.10 degreesC) higher than the average. Therefore, the twentieth century seems the warmest one in China for the last millennium or more. The last millennium was not the wannest one in comparing with others for the last 10 millennia. Ten regional temperature series from 10 ka BP to the present were analysed with the same time resolution (250a) and identical normal (1880-1979). Gaps in a few series were filled by the data from previous work. Average temperatures were also found on the basis of area weighting of regional series, showing that the Megathermal was manifested well in China, with temperatures for the period of 8.0 to 3.0 ka BP from 1.5 to 2.0 degreesC higher than the present. Studies of the relationship between temperature and precipitation indicated no consistent correlation. However, warm-dry dominated over warm-wet climate in north China, but the opposite is the case in the very south and in the west. In east China, the twentieth century was probably the driest one during the last millennium. Severe droughts occurred in 20 of the 100 summers of 1900-1999, but the mean frequency was only 10.6 per century.