Winter temperature variations over the middle and lower reaches of the Yangtze River since 1736 AD

We present statistically reconstructed mean annual winter (December-February) temperatures from the middle and lower reaches of the Yangtze River (24A degrees N-34A degrees N, 108A degrees E-123A degrees E within mainland China) extending back to 1736. The reconstructions are based on information regarding snowfall days from historical documents of the Yu-Xue-Fen-Cun archive recorded during the Qing Dynasty (1644-1911). This information is calibrated with regional winter temperature series spanning the period from 1951 to 2007. The gap from 1912 to 1950 is filled using early instrumental observations. With the reference period of 1951-2007, the 18th century was 0.76 A degrees C colder, and the 19th century was 1.18 A degrees C colder. However, since the 20th century, the climate has been in a warming phase, particularly in the last 30 yr, and the mean temperature from 1981 to 2007 was 0.25 A degrees C higher than that of the reference period of 1951-2007, representing the highest temperatures of the past 300 yr. Uncertainty existed for the period prior to 1900, and possible causes of this uncertainty, such as physical processes involved in the interaction between temperature and snowfall days and changing of observers, are discussed herein