Bradley, R. S., H. F. Diaz, P. D. Jones, and P. M. Kelley, 1987: Secular fluctuations of temperature over Northern Hemisphere land areas and mainland China since the mid-19th century. In The Climate of China and Global Climate, D. Ye, C. Fu, J. Chao, and M. Yoshino (Eds.), China Ocean Press and Springer-Verlag, 76-87.
A comprehensive set of long-tern temperature station records from throughout the Northern Hemisphere has been used to produce a gridded data set for studies of long-term climatic variability. Arealy weighted and normalized seasonal average temperatures for Northern Hemisphere land areas and for mainland China have been computed for 1851-1980 and 1881-1980, respectively. Both records show similar trends; temperature increased from the late 19th century to a minimum in the 1940s followed by a cooling trend which has reversed over the last 10-15 years. In the Northern Hemisphere record, temperatures appear to have decreased from the 1850s to the 1880s but the spatial coverage is poor during this period. Data from China are highly correlated with Northern Hemisphere land area data, suggesting that long-term proxy records for China will provide valuable indications of climatic fluctuations over a much larger area. Extremely sharp drops in temperature, particularly in Fall months, occurred after several major volcanic eruptions. High temperatures are sometimes associated with major El Niño years. On occasions, when an El Niño event has followed a large explosive eruption, the two opposing effects have tended to minimize the climatic fluctuation which would otherwise have resulted.