Studies On The Temperature Changes In Instrumental Period In China

In this paper, based on the instrumental surface air temperature data in China as many observation stations as possible, which have been looked though, corrected and made interpolation, China's surface air temperature time series in the recent 100 years and more have been re-calculated and extended by adopting new statistical method for calculating mean temperature and area weighted average method. The temperature change trends, periods as well as abrupt changes in the recent 100 years and more in China are analyzed and discussed. And the future temperature change trend has also estimated.Because of past history, there are some problems as gaps of observation, mistakes and an observation norm without unification etc. in the data before 1950. Being aimed at these problems, the works have been finished as follows: firstly, the data set used in this paper have been quality-controlled by means of the comparison of annual mean values, the relationship between three (mean, maximum and minimum) temperatures and triplication standard error. Consequently, the quality-higher data set has been obtained. Based on the more reliable data set, the data series minus some observations have inserted and partly prolonged by adopting difference correction method on possible condition. Secondly, after the different methods of calculating mean temperature and its influences on the results are analyzed and discussed, adopting the mean temperature derived from maximum and minimum temperature, accordingly, the homogeneity and quality of China's surface air temperature time series are markedly improved. Thirdly, the representativeness of China's surface air temperature time series is analyzed decade after decade. The results display that the series can reflect the climate change of approximately half China during 1870s–1890s; From the early 20th century on, the series has already had definite reliability; since 1921, it has had higher reliability.The results of this research show that since 1873, the climate in China has shown an evident warming trend. The annual mean temperature has risen by about 0.96℃. The annual mean maximum and minimum temperatures have respectively risen by about 1.20℃and 0.70℃. Since the early 20th century, the annual mean temperature has approximately risen by 0.80℃; Since 1951, it has risen by about 1.13℃. According to the analysis for the temperature fields, there are two remarkable warm periods during the late 1920s–1940s and 1980s in China, but with obvious differences between them. The first warming is not countrywide, in which its center mainly lie in the region between 30oN and 40oN and the warming range in the central and western portions is more than that in the eastern part of China. The second warming occurred firstly to the north region of 35oN, and afterward extended all but to the whole of China after the middle 1990s. This warming is countrywide, but then the strongest warming region is to the north of 34oN. Besides, the climate alternated more frequently between warm and cold during the middle 1950s–the middle 1980s, which is generally a countrywide change.The temperature change trends have obviously regional differences in China. In the recent 55 years, the most remarkable warming regions lie mainly to the north of 34oN, and the warming in Qinghai-Xizang plateau is also obvious; But then the warming in the southwest is not obvious, and the warming extent in the rest of the south is less. The distributions of maximum and minimum temperature change trends are a certain extent similar to that of the mean temperature. But the warming rates of minimum temperatures are much greater than those of maximum temperatures in most of the regions in China. And the maximum temperature change trend is not evident in the south. As far as all country average is concerned, the change extent of the minimum temperature is greater than that of the maximum temperature in the recent 55 years, which shows that the temperature change during the nighttime hours plays major role in the change of the mean temperature. As a result of the greater extent of low in 1950s–1960s and of high after 1980s, the warming rate of minimum temperature is much more than that of maximum temperature. Besides, a remarkable adjustment of the atmosphere general circulation occurred in the middle and late 1970s. The average daily range before the adjustment is relatively greater. However the one after the adjustment is relatively less.The change trend and fluctuation feature of the mean temperature in China are to a great extent consistent with those of global and hemispherical mean temperatures, but there are also some differences. First, the fluctuation extent of the mean temperature in China is greater than one of northern hemisphere in the corresponding period. Second, there are two highly notable warm periods in China, which occurred respectively during 1930s–1940s and after 1980s. Although the second warm periods of the globe and hemispheres are very strong, their first warm periods are apparently weaker. The global average surface air temperature has increased by 0.72℃since 1873, and the China's one of the same term has increased by 0.96℃, which is higher by 0.24℃than that of the globe. But the increased extent of China's average temperature is not all the time higher than that of the globe. According to the results that the beginning years are before 1920s, the ratios between both are about 78%–133%. Some of them are rather adjacent, for example, the increased extent of 0.78℃during 1890–2005 in China is equal to one of northern hemisphere, and merely higher by 0.03℃than one of the globe. The analysis results show that while the time scale is shorter, there is greater difference between the temperature change trends of China and globe. However, from the point of view of the long-term change trend with longer timescale, their difference tends to diminish.Using wavelet analysis technique and moving-t test method, the multi-time scale character as well as the periods and the abrupt change points for the air temperature change in the last 133 years in China are analyzed. The results indicate that there is the oscillation period 64–71 years for China's air temperature changes in the last 100 years and more, which has the strongest extent and plays major role during 1926–2005. It is basically consistent with the oscillation features of the climate in East Asia and the globe. In addition to the major period, the oscillation period 34–40 years is rather obvious during 1873–1925. And there are a number of scale periods, but they only occur in some shorter periods of time. These shorter time-scale oscillations bring forth the short-term fluctuations of the air temperature in China.The abrupt change analysis shows that the air temperature changes experienced three abrupt changes with the timescale around 20–30 years in the last 133 years in China, which occurred respectively in 1925–1932, 1986–1988 (cold–warm) and 1950–1956 (warm–cold). There are other two abrupt changes with the timescale around 15 years, occurred respectively in 1888–1889 (cold–warm) and 1905–1907 (warm–cold). The strongest air temperature change in the transitional process from cold to warm in 1986 occurred basically in the north of China. Although the climate in the south of China changes from cold to warm at the same time, the warming extent is weaker than that of the former. This shows that the strong warming in the north of China plays main role in the abrupt change.The period analysis displays that the current climate is about the center of the positive phase of the oscillation period, and in the future period of time the air temperature will still continue in the higher position. However, the abrupt change from warm to cold is likely to occur approximately in 2020–2025. But then this abrupt change express only that the position of the climate oscillation change from the positive phase to the negative phase. If considering the influences of the continuous warming of climate on it, it will be the possible result that the air temperature oscillates on a higher level of average value, and does not simply return to the primary jumping-off point.Looking to the future, some further studies, such as advancing the representativeness of the early series, analyzing and estimating the impacts of the environmental factors like urban heat island effect etc. on the temperature changes as well as discussing the possible causes of the climate change in China and so on, should be planed and made.