THE PULSATION OF WORLD CLIMATE DURING HISTORICAL TIMES
CO-CHING CHU(Academia Sinica)
In the past the question whether world climate has changed during historic times has been very controversial. The accumulation of meteorological data and other relevant facts in the N. hemisphere during the last 60 years gives undeniable evidence of a general warming up during that period, especially in the high latitude. China is no exception. Not only that mean annual temperature of various regions has increased during the first half of the 20th century, recent exploration in Tien-shan and Nan-shan in N. W. China, Karakoran and Himalaya in the S. W., provides ample proof of retreats of existing glaciers; the Mozard glacier on the E. slope of Khan Tengri, e. g., retreated 750 meters during the period 1909-1959. And these glaciers are still retreating in recent years.The pulsation of climate does not limit itself to recent times, but can be traced through historical periods to the Quaternary. Results of works of A. V. Shnitnikof of U. S. S. R., C. E. P. Brooks of Great Britain, and H. W. Ahlman of Sweden, among others, were cited. In China, phenological records were kept as early as 500 B. C. And because of significance of phenological records to the agricultural calendar, which was promulgated in 102 B. C. during the reign of Wu-ti of Han dynasty, and used by the Chinese farmers practically unaltered throughout the last 2000 years, these records are an invaluable source of tracing the ancient climate.The phenological materials contained in the diaries and poems of Chinese writers in the past are so rich that it deems sufficient to delineate a general outline of climatic variation in China for the last 1500 to 2000 years from the result of analysis of these materials. The paper takes up the second half of the 17th century as an example, and it was found from the dates of freezing of Grand Canal, the flowering dates of peaches and apricots kept in Hangchow and Soochow, and the number of severe killing frosts in the citrus gardens of Kiangsi Province that the period must be much colder than present. This period happens to be what is called "The Little Ice Age" in W. Europe.Finally, the paper touches upon the cause of climatic variation, and maintains that the fluctuation of solar radiation is the main factor. The number of times sun spots and aurora borealis which had been observed in China from the second century to the 17th were tabulated along with the number of severe winters in each century, and found their correlation rather close.