The rise and fall of Tang state

Tang Dynasty/Climate Change/Rise and Fall

Upper guide bearing

The Tang Dynasty was the most powerful feudal dynasty in China, with strong economy, prosperous cities, prosperous culture, numerous talents, vast territory and strong national strength. In the past, the reasons for the civilization of the Tang Dynasty were mostly investigated from human factors, and the reasons were found from historical accumulation and enlightened monarchs. This is an important perspective. In recent years, scholars have noticed that the warm climate period often corresponds to the prosperity of the feudal dynasty in China.

However, what is the basis of this warm and humid environment and the mechanism of civilization prosperity? What does this mechanism have to do with the accumulation of history and the role of enlightened monarchs? This paper intends to solve this problem from the relationship between climate change and the history of Tang Dynasty. Moreover, historians all know that the Tang Dynasty was the heyday of feudal society in China, and the years of Kaiyuan and Tianbao were also the heyday of the Tang Dynasty, which was also the turning point from prosperity to decline. During this period, "An Shi Rebellion" was an important landmark event. To some extent, the Anshi Rebellion is a very interesting turning point in China feudal society, and whether this turning point is intrinsically related to the climate change in the Tang Dynasty is the second question to be solved in this paper.

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1. The Tang Dynasty was a warm period in the history of China.

Mr. Zhu Kezhen thinks that the 7th century is a warm and humid era, which is mainly based on the comparison between the phenology of plum trees and oranges and the growth period of crops, and then draws a conclusion from the perspective of phenology, which is proved by the climate characteristics reflected by Norwegian snow line and Greenland ice. (Note: Zhu Kezhen's Preliminary Study on Climate Change in China in the Last Five Thousand Years, China Science No.2, 1973. ) Since then, although some people have made some amendments to this (Note: In recent years, Mr. Mou Chongxing has written "Re-textual Research on Climate Change in China in Five Thousand Years" (Meteorological Press, 1996), which systematically discusses Zhu Kezhen's viewpoints and historical materials. ), but almost all historical geography monographs and textbooks follow Zhu Lao's theory and set the Tang Dynasty as a warm period. Such as Ma's Introduction to Historical Geography of China, Zhang Butian's Historical Geography of China, Zou Yilin's Introduction to Historical Geography of China, Shi Nianhai's Outline of Historical Geography of China, Zhang and Zhang's Outline of China's Historical Theory, etc. Zhang Jiacheng's Climate Change and Its Causes, China Academy of Sciences' Physical Geography and Historical Physical Geography of China, Gong Gaofa's Changes of Climatic Zones and Evolution of Biological Distribution Lines in China's Historical Period, and Taiwan Province scholar Liu's Changes of Historical Climate in China also support the warm current theory in Tang Dynasty.

However, some scholars put forward new ideas and denied the warmth theory in Tang Dynasty. Man Zhimin is a representative. He first wrote a paper entitled "Study on the Climate Change Stages and Characteristics in Tang Dynasty" in the eighth edition of Historical Geography published by 1990. He objected to the warm period of Tang Dynasty and put forward a new theory that it turned cold after the middle of Tang Dynasty. Subsequently, it was further elaborated in China Climate and Sea Level edited by Shi Yafeng, Historical Geography of Huang-Huai-Hai Plain edited by Zou Yilin and Climate Change Theory in Tang Dynasty. The main reason is that Shu Mei, dried tangerine peel and tamed elephant in Chang 'an have artificial protection measures, which can not be used as indicators of climate warmth, reinterpreting the growth period of crops. At the same time, it lists many evidences of cold in Tang Dynasty. Recently, Wang Zheng and others suggested that the climate in the Tang Dynasty was in the state of Joas, which was unstable (Note: Wang Zheng and others "The Influence of Historical Climate Change on the Social Development of China", Journal of Geography 1996, No.4). )。

The author believes that from the current overall research, the evidence of the theory of temperature and humidity in Tang Dynasty is more sufficient.

(1) Man Zhimin thinks: "Therefore, compared with modern times, the distribution area of citrus economic planting in Tang Dynasty can't reach the conclusion that the climate in China in Tang Dynasty was warmer than modern times, and the climatic zone moved northward by more than one latitude." The author believes that Mr. Man Zhimin did not separate the two different concepts of the location of local tribute at the national level from the distribution of the northern line. Generally speaking, subtropical and tropical cash crops become local products or local taxes at the national level. Climate factors should be very suitable for this plant and have considerable tolerance, so only excellent varieties can become local products and local taxes. For example, today's Ezhou and Xiangzhou can grow oranges, but they cannot become the national quality of local products. In fact, according to the author's research, Xizhou is located in Heishui County, northwest Sichuan. Today, there is almost no citrus production in this area. The annual average temperature is 9. 1 degree, the monthly average temperature of 1 degree is only-1 degree, and the annual rainfall is 827.7 mm, but it is an important citrus producing area in the Tang Dynasty, with the quality of local tribute. This shows that the annual average temperature in this area is about 4 degrees higher than it is now, and the average temperature in 65438+ 10 is about 3-4 degrees higher. Similarly, Bazhou and Mianzhou in the Tang Dynasty were also important places for citrus tribute. But although it is produced today, it is far from the quality of local tributes.

(2) The author agrees with Man Zhimin's conclusion that the reliability of climate characteristics indicated by tame elephants and artificially protected plum trees, oranges, lychees and bamboos is not high, but there are some differences with Man Zhimin in the identification of cold climate indication records. The author thinks that the reliability of "cold" and "great cold" in winter in the Yellow River basin in China is not high, because on the one hand, "great cold" and "cold" here are not qualitative, indicating that the temperature can be high or low; On the one hand, on the contrary, winter "cold" and "severe cold" in middle and high latitudes are more normal, but it is not cold that makes them abnormal. Therefore, it is of little significance to count the "great cold" and "cold" in these areas in the Tang Dynasty. This is as insignificant as counting the heat in the south of China. On the contrary, statistics such as "it doesn't snow in winter" in northern China and "frozen rivers" in southern can better explain the climate. Based on this understanding, the author thinks that there is no ice and snow in Guanzhong area of Tang Dynasty 16 years calculated by Zhu He, and it is more credible to explain the warmth of Tang Dynasty with "this is unique in the history of China". Taiwan Province Province Liu's "Climate Change in the History of China" holds that: "During the 300 years of the Tang Dynasty, there were relatively few years of heavy snow and extremely cold summer frost in Xia Xue, but the number of years without snow in winter was as many as 19, ranking first in China's history". According to the study of phenology and citrus distribution, experts also show that the average annual temperature in the Tang Dynasty was about 1 degree higher than it is now. (Note: Liu's book Climate Change in the History of China is quoted from Xiong's book Climate Change in China, Bulletin of American Meteorological Society, Vol. 55,No. 1 1 month, 1974. Wu Hong Qi also talked about Yang Renhuai's research on sea level change and temperature fluctuation since 2000, and explained that the 8th century to 1 0th century was a warm period, when the annual average temperature was about1degree, which was called "small high temperature period". According to the climate, snow line and vegetation studied by Yu Xixian, Duan Wansha and Gong Gaofa, it is considered that the annual average temperature in Tang Dynasty is about 1 degree higher than that in modern times, and the latitude of climatic zone is about north latitude 1 degree. (Note: Wu Hong Qi, et al. "Cold and Warm Climate Characteristics and Climate Fluctuation in Sui and Tang Dynasties", Quaternary Studies 1998 1. )

(3) The same is true of the research results of regional climate in Tang Dynasty. Some scholars have seen from the cold changes in Henan's historical period that the Sui and Tang Dynasties were "mainly warm, and then turned cold". (Note: Sheng Fuyao's "A Preliminary Study of Cold and Warm Changes in Henan's Historical Period" is the seventh in the historical geography series. The curve of Jiangsu temperature change index established by Chen Jiaqi et al. since 2000 shows that the longest duration of relative warm period is in the 7th and 8th centuries, that is, before the middle Tang Dynasty, and there are few records of winter in this period. (Note: Chen Jiaqi et al. Study on Climate Change in Jiangsu in Recent Two Thousand Years. Geographical Science, No.3, 1998. ) The northern boundary of litchi planting in the upper reaches of the Yangtze River in the Tang Dynasty was two latitudes higher than it is now, so it can be inferred that the annual average temperature in the upper reaches of the Yangtze River at that time was about 1-2 degrees higher than it is now. (Note: Lan Yong's Evolution and Temperature Fluctuation of the Northern Boundary of Litchi Distribution in the Upper Reaches of the Yangtze River in Recent 2000, Quaternary Studies 1998 1. According to Guo Shengbo's research, litchi grew in Chengdu in Tang Dynasty, but not in Southern Song Dynasty. (Note: Guo Shengbo's Litchi in Chengdu and the Cold Climate in the 12th Century, China Historical Theory Series, No.3, 1989. ) In another poem by Zhang Ji in the Tang Dynasty, "Kapok blooms in Jiangxi", we can see that there was kapok in Chengdu in the Tang Dynasty, and both kapok and kapok are warm plants. Today, these two plants do not exist in a natural state in Chengdu, indicating that the temperature in Chengdu in the Tang Dynasty should be higher than now. According to Du Fu's poem "Singing Rain" in Chengdu, Liu's "Climate Change in the History of China" talks about the rainy weather in April of the lunar calendar, and thinks that there is no rainy weather in Chengdu at the turn of spring and summer, which also shows that Chengdu in Tang Dynasty is warmer and wetter. According to Xin Tang Shu and Schumann, the growing season of Yunnan and Zhejiang silkworms is generally born in January and cocoons in February. We know that silkworms are very demanding on temperature, and the average monthly temperature is lower than 20 degrees, which may be affected. The optimum temperature is 16℃ to 2 1℃, and when the temperature drops below 7.5℃, they will enter a dormant state. It can be seen that the optimum temperature period of silkworm is much earlier than now, indicating that the annual accumulated temperature in Yunnan-Guizhou Plateau was higher than now. The songs contained in volume seven of Schumann and the agricultural solar terms in the south of Jingzhou and the west of Dianchi Lake have been debated greatly in past dynasties. By comparing the solar terms of Zhaotong bazi and Dianchi bazi, the author found that rice was sown in March and April and harvested in August in the Tang Dynasty, but now these areas are sown at the end of April and harvested in October in the lunar calendar. It can be seen that the rice growth period is now delayed and extended, which indicates that the accumulated active temperature in Yunnan has decreased and the crop growth period has been shortened.

(4) The Tang Dynasty was not only warm, but also very humid. Zhu Kezhen's article "Climate Change in the History of China" counts the droughts and floods in China in past dynasties, indicating that the Tang Dynasty was an era with relatively few droughts. Statistics in the second volume of China's Natural and Man-made Disasters in Past Dynasties show that the period of Sui, Tang and Five Dynasties was the period with the highest proportion of floods in the history of China, which may be related to abundant rainfall at that time. Lu Weiguang's Drought in North China (Geography, Vol.1, No.2, 1937) holds that during the Han and Tang Dynasties, rivers outside the Great Wall were generally abundant today. Further research also shows that the 200 years from 630 to 834 is the longest rainy period in the past 3000 years. (Note: Wang Xiang and Wang, Climate Change in the Central Plains of China in the Last Five Thousand Years, China Science Series B, 1987, 1. ) It can be seen that the climate in the Tang Dynasty was really humid.

In a word, it seems credible that the Tang Dynasty was a warm and humid period in the 2000-year history of China.

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2. The influence of warm and humid climate on agricultural economy in Tang Dynasty.

(A) the impact of climate change in the historical period on agricultural production in China.

Mr. Wang Zijin once studied the relationship between climate change and historical development in the Qin and Han Dynasties, and thought that the climate changed from warm to cold and the migration direction showed a general consistent trend from northwest to southeast in the Han Dynasty. The household registration changes in Guanzhong, North China Plain and Jiangnan and the river disaster further proved this correlation. (Note: Wang Zijin's Historical Investigation of Climate Change in Qin and Han Dynasties, Historical Research No.2, 1995. This shows that the influence of climate change on the social development of Qin and Han dynasties is very obvious.

From the perspective of historical geography, the century-long scale climate change has a great impact on high-latitude nomadic areas in East Asia (north and south of the desert), traditional agricultural areas in mid-latitude of China (Yellow River basin) and low-latitude underdeveloped areas in south China (Yangtze River basin and Pearl River basin).

The influence of (1) on high-latitude nomadic areas in East Asia. The research shows that the survival of nomadic people depends greatly on the grassland ecological environment, and the influence of temperature fluctuation and rainfall change on animal husbandry production is often fatal. Up to now, the "white disaster" in grassland area is still one of the most serious natural disasters. In the Middle Ages, when productivity was low, the traditional nomadic people were more dependent on nature than the agricultural people at that time. The research shows that the correlation coefficient between forage yield and summer rainfall in some places in Inner Mongolia grassland is 0.68. 1980 the low temperature and lack of rain in summer shortened the growth period of forage by three fifths, and the cold climate led to the death rate of livestock as high as 90% in winter and spring in some places. (Note: Meteorological Bureau of Xianghuang Banner, Inner Mongolia, etc. Study on Climatic Conditions of Forage Growth, Chinese Grassland, No.2, 1984. This temperature fluctuation often affects the migration pattern of nomadic people. The nomadic people in high latitudes of China formed a periodic general trend of southward advance during the cold period. On the contrary, if the climate is warm and humid, the grassland ecological environment is good, the production of nomadic people is relatively normal, the society is often relatively stable, and the influence on the agricultural people in South China is relatively small, and the pressure on the northern part of the agricultural people in South China is relatively small, which is conducive to the development of agricultural production in the Yellow River Basin.

(2) Impact on traditional agricultural areas in mid-latitude. According to Ni's research, the general trend of climate change in mid-latitude areas in northern China in historical period is increasingly dry and cold, which causes the humid and semi-humid areas in China to withdraw southward, the arid and semi-arid areas to expand southward, and the agricultural and pastoral areas to move southward, shortening the period suitable for crop growth and reducing maturity; At the same time, it also causes the frequency of natural disasters to increase, the ecological environment to deteriorate, the water source to decrease, and the benefit of water conservancy projects to decline; The planting of rice in the north has shrunk, and the yield of single grain has decreased; At the same time, the distribution of economic crops and economic animals moved southward (note: Ni Zhu's On the Impact of Climate Change on Agricultural Economy in Ancient North China, Agricultural Archaeology 1988 1. )。 On the other hand, if the climate gets warmer and wetter, the farming-pastoral line moves northward and the agricultural area expands; Climate warming often reduces the frequency of natural disasters and makes agricultural production relatively stable. Climate warming makes the growth cycle of crops longer, the number of mature systems increases, the multiple cropping index increases and the total output per unit area increases; Because of the hot and humid climate, the growth period of single-season crops may be short, which provides more time for improving the multiple cropping index while increasing the single-season yield. At the same time, the warm and humid climate makes the water source more abundant, the rice planting area expands, and the grain output increases, while bamboo and mulberry grow better in the north. The output diversity with biodiversity often makes the northern region have more agricultural economic growth points. That is to say, in the Yellow River valley in the north of China, the warm and humid climate is often more conducive to the development of agricultural economy, which is the basis for the development of traditional feudal society in China.

(3) Impact on the underdeveloped areas south of low latitude. The impacts of climate change on the Yangtze River Basin and the Pearl River Basin in China are complicated. This complexity mainly comes from two aspects. On the one hand, the study of historical geography shows that the climate change range in the middle and low latitudes in China is much smaller than that in the middle and high latitudes in the historical period, that is to say, the climate change range in the Yangtze River basin, especially in the Pearl River basin, is small and has little impact on the environment. On the one hand, the underlying surface in southern China is relatively more complicated, including mountains, hills and flat dams, while surface water resources are abundant. In ancient and medieval times, some areas were still in the primitive ecological state. With the improvement of human productivity, the influence of human factors on the development of these areas is often more obvious. Mr. Wang Zijin once thought that the increasingly dry and cold weather after the Eastern Han Dynasty was the natural condition for the development of hukou in Changsha, Guiyang and Lingling areas in the middle reaches of the Yangtze River, which made the "low humidity" areas develop better. It seems reasonable in theory, but the relationship between them may need to be further explored. Because the Tang Dynasty was wetter than the Eastern Han, Wei, Jin, Southern and Northern Dynasties, and the southern region was more developed, the "humble and humid" environment was improved. In fact, from the perspective of climate change, if the southern region is drier and colder, it will have a greater impact on the agricultural economy. From this point of view, the development of the southern region may still be affected by the great transfer of civilization between North and South, and human factors may be even greater.

With the progress of production technology, theoretically, the impact of climate change on agricultural production is relatively weakened. However, according to Bai Yang and others' research on the dynamic changes of agro-climatic zone boundary in subtropical areas of China in recent hundred years, the northern boundary of north subtropical zone and middle subtropical zone fluctuated by two latitudes in recent hundred years, including the northern boundary of double cropping rice 1 latitude and the northern boundary of citrus 1 latitude. The impact on agricultural production is still great. (Note: Bai Yang, et al., "The Dynamic Change of Agroclimatic Zone Boundary in Subtropical Area of China in Recent 100 Years and Its Impact on Agricultural Production", Journal of Natural Resources, No.3, 1993. It can be seen that the impact of long-term climate change on agricultural production can not be underestimated until now, let alone in the Tang Dynasty.

(B) the impact of warm and humid climate on the agricultural economy in the Tang Dynasty

(1) The dividing line between agriculture and animal husbandry moved northward, and the agricultural area expanded. In the Tang Dynasty, with the warming of the climate and some human factors, the northern line of agricultural and pastoral areas moved northward. According to scholars' research, from the Warring States Period to the early Western Han Dynasty, there was a dividing line between agriculture and animal husbandry from Hehuang area in eastern Qinghai to the northeast, passing through the upper reaches of Jinghe River, Weihe River and Beiluohe River in northern Shaanxi and Longdong, Longmen Mountain in the southern edge of Shanxi-Shaanxi Canyon Basin in northwest Shanxi, and connecting Yan Qin Changcheng to Liaoning along Luliang Mountain and Hengshan Mountain in the northeast. During the reign of Emperor Wu of the Han Dynasty, he conquered the northern Xiongnu and established forty-four counties. The agricultural reclamation area moved northward, and the northern line of agriculture and animal husbandry moved to Xida Hetao, Hexi Corridor, West Wulanbu Desert and Helan Mountain in Huangshui Valley, the yinshan mountains in the north and along the Great Wall in the east. However, since the Eastern Han Dynasty, the northern nationalities moved southward, which disrupted the boundaries between farming and pastoral areas and formed a criss-crossing transitional zone between farming and pastoral areas. (Note: Zou Yilin's Historical Geography of China (16 1), Fujian People's Publishing House, 1993. )

According to textual research, in the Tang Dynasty, the boundary between agriculture and animal husbandry became the boundary between farming area and semi-farming and semi-grazing, and moved northward. For example, the eastern section moves northward below the Yanshan Mountains, the southwest end extends southward to the west of Longshan, and the northeast end can also extend to the lower reaches of Liaohe River. Semi-agricultural and semi-pastoral areas and pastoral areas also form a dividing line, that is, from the yinshan mountains to Juyanhai in the west and Yanshan Mountains in the east. In this case, some developed and wealthy areas have formed in agricultural areas, such as the lower reaches of Jingwei River, Fenshui River, Sushui River Basin, Luo Yi and the Yellow River. In semi-agricultural and semi-pastoral areas, there is already a considerable agricultural foundation. (Note: Shi Nianhai's Changes of Farming and Pastoral Areas in Sui and Tang Dynasties and Their Influence on the Rise and Fall of Dynasties, Historical and Geographical Studies in Tang Dynasty, China Social Sciences Press, 1999. This not only expanded the agricultural areas in the Tang Dynasty, but also provided a buffer zone between agricultural areas and pastoral areas, which enabled the frontier defense in the Tang Dynasty to be supported by certain local materials, enhanced economic strength, strengthened military defense, and made the society more stable. This is not only directly beneficial to the economic development in the Tang Dynasty, but also creates a more stable social environment for the development of agricultural economy. Since the Song and Yuan Dynasties, the climate in northwest China has become more and more arid and less rainy, with animal husbandry as the mainstay and backward economy. However, in the Tang Dynasty, troops stationed in the western regions settled the fields, which led to the northwest Longyou region meeting with each other, and Sang Ma withered in the wild (Zi Jian (Volume 2 16)). ), the Northwest Silk Road is also very smooth.

(2) The northward shift of agricultural cash crops made the yield diversity more obvious. Due to the warm and humid climate, the northern boundary of agricultural cash crops in the Tang Dynasty was northerly, such as rice, sericulture, bamboo and citrus. In this way, the diversity of output provides better conditions for the development of agricultural economy. Ni's research on Zhang's introduction showed that single-season rice was planted in the Yellow River basin during the warm period of historical climate, and double-season rice could be popularized to both sides of the Yangtze River. During the cold wave, single-season rice was widely planted in Huaihe River Basin, while double-season rice was more common in Lingnan area. The change of climate in historical period can cause the north-south change of planting area of single and double cropping rice, and the change range is about two latitudes. (Note: Ni, On the Impact of Climate Change on Agricultural Economy in Ancient North China, Agricultural Archaeology 1988 1. According to research, paddy fields were widely developed in the Yellow River Basin in the Tang Dynasty. Rice planting starts from Hexi Corridor in the west, reaches Hetao and the southern foot of Yanshan in the north, reaches Qinling and Huaihe rivers in the south and reaches the sea in the east. The northern line is farther north than before and after, and its distribution area is wider. (Note: Zou Yilin, Geographical Distribution and Environmental Constraints of Rice Production in the Yellow River Basin in Historical Period, Journal of Fudan University, No.3, 1985. In the Tang Dynasty, the Yellow River valley was also an important sericulture producing area, including Henan, Zhengzhou, Ruzhou, hua county, Bianzhou, Songzhou, Chen Zhou, Xuzhou, Yanzhou, Mizhou, Zhouzhou, Xiangzhou, Weizhou, Zhou Bei, Youzhou, Jizhou, Zhaozhou, Anton, Jinzhou, Fenzhou and Dave. (Note: Zhao Feng's "The Geographical Distribution of Sericulture in Tang Dynasty", China Historical Geography Theory Series No.2, 199 1. The author thinks that the development of sericulture in high latitudes is caused by the warm climate in Tang Dynasty. In the Tang Dynasty, there were large areas of bamboo forests in the Yellow River basin. In the Song Dynasty, some bamboo roots were found in the northern region, which may have been left over from the Tang Dynasty. Meng Qian Bi Tan by Shen Kuo in the Northern Song Dynasty (Volume 2 1): "In recent years, the bank of Yongningguan in Yanzhou collapsed and was buried dozens of feet underground, looking for bamboo shoots under the soil. Hundreds of stems are connected and turned into stone. " Luo Dajing's "He Lin Yu Lu" in the Southern Song Dynasty said in Volume 4: "I heard that there was no bamboo in Qin, and there was a landslide in. Therefore, bamboo was produced in ancient times. " Therefore, during the Sui and Tang Dynasties, some counties in Guanzhong area had bamboo supervisors. This trend of moving northward is also manifested in the southwest. As mentioned above, the distribution of litchi in the Tang Dynasty moved northward by two latitudes, and the citrus planting center in southwest China was two latitudes higher than it is now. The distribution of edible banana (M.paraddisiala var sapientum) and ornamental banana (Musa basjoo) in China in the Five Dynasties and the Northern Song Dynasty was also northward than it is now. ) I miss the Tang Dynasty.

In this warm and humid climate, the water resources in the northern region are more abundant. According to Mr. Wang Lihua's research, the water environment in the middle and lower reaches of the Yellow River in the Middle Ages was still good, and fish resources in rivers and lakes were abundant, so fishery production still played an important role in social and economic life. (Note: Wang Lihua's Water Environment and Fishery Production in the Northern Region in the Middle Ages, China Historical Theory Series No.4, 1999. )

(3) It can increase crop growth time, shorten crop growth cycle and improve multiple cropping index. Due to the warm and humid climate and good heat conditions, the available time for crop growth in the Tang Dynasty increased, and the growth period of crops in the warm and humid period of the Tang and Five Dynasties was longer than now 10 days. (Note: Gong Gaofa et al. Climate Change and Its Impact on Agricultural Production, Collected Works of Zhu Kezhen, Memorial Scientist, 195 to 2 12, Science Popularization Press, 1982. )

According to Zheng's research, wheat was harvested in April in Tang Dynasty and May in Song Dynasty. Similarly, the collection time of the two taxes in the Tang Dynasty was more than one month earlier than that in the Song Dynasty. (Note: Zheng, "The southward movement of China's ancient economic center and the study of Jiangnan economy in Tang and Song Dynasties", Yuelu Bookstore, 1996. The delay of wheat harvest time will inevitably affect the growth of other crops in multiple cropping rotation.

Double-cropping rice was popular in Lingnan in Tang Dynasty and Fuling in Chongqing in Tang and Song Dynasties. Therefore, the Jade Emperor Jisheng Volume 174 quotes Guiling Record: "When the early rice is ripe in May and a half, it can be eaten new. It will be harvested in July and August. " At the same time, litchi produced in Fuling area in Tang Dynasty was of good quality, which also showed that the local climate was warmer than now.

"Schumann" Volume 7 says: "There are Congqu and Jingzhou in the south and Dianchi Lake in the west. The local customs are mainly paddy fields, and hemp, beans, millet and millet cannot grow in the town. Paddy fields are ripe once a year, and rice is harvested in August. It is convenient to grow barley in paddy fields at the turn of November, and it is ripe in March and April. After barley is harvested, japonica rice is also planted. " Wheat is planted in the mountains and harvested in late February/kloc-0, for example, wheat and barley are harvested at the same time in March. "This is the earliest recorded rice-wheat double cropping system in China. Some scholars also talked about the double cropping system of rice and wheat in the lower reaches of the Yangtze River in the Tang Dynasty. The popularization of rice-wheat double cropping system in Tang Dynasty may be related to the warm and humid climate and the increase of crop growth time in Tang Dynasty.

It is not difficult to imagine that it can increase the growth time of crops, shorten the growth cycle of crops, improve the multiple cropping index and increase the yield per unit area, which is naturally beneficial to the development of agricultural economy in Tang Dynasty.

(4) The single-season output has been increased, and the total grain output has been increased. The research shows that in the middle and high latitudes of northern China, the warm climate reduces the frequency of natural disasters, and the warm climate itself is also beneficial to the growth of crops, which makes the output of many food crops increase in the Tang Dynasty. According to Mr. Wu Hui's research, the grain yield per mu in ancient China was the highest in the Tang Dynasty before the Yuan Dynasty, reaching 334 Jin. (Note: Wu Hui's Calculation of Grain Yield per Mu in Qing Dynasty, Agricultural Archaeology 1988 1. Wang Zheng's research shows that the proportion of tax and grain in northern China in Tang Dynasty was 75.9%, that in northern China in Northern Song Dynasty was 54.7%, and that farmland was only 3 1%. Later, the proportion of cultivated land in the north was higher than that of tax grain, indicating that the productivity level of land in the north was higher than the national average in the warm period, and the opposite was true in the future. (Note: Wang Zheng et al. Influence of historical climate change on social development in China. Journal of Geography, No.4, 1996. )

(5) remarkable achievements have been made in water conservancy construction. The warm and humid climate is beneficial to the development of water conservancy construction, especially in the Yellow River Basin of China at middle and high latitudes. The research shows that before the middle Tang Dynasty, the water conservancy projects in the northern region were completely restored and some irrigation areas were newly built. Especially the success of irrigation from the Yellow River and the restoration of water conservancy in Guanzhong. According to Li Jiannong's Draft of China Ancient Economic History, there were 253 water conservancy projects in the Tang Dynasty and 1048 in the Song Dynasty, but there were 103 projects in the northern part of the Tang Dynasty and only 78 projects in the northern part of the Song Dynasty. This shows that the agricultural water conservancy construction in the northern region of Tang Dynasty was very prominent. This played an important role in the prosperity of Tang civilization with the north as the core area. After the middle Tang Dynasty, water conservancy construction in southern China continued to develop, and land use forms such as hutian, Shatian, Putian, Shetian and terraced fields have been frequently recorded. Among them, the most remarkable is the formation of Tangpu polder in Taihu Lake Basin (Note: China Historical Draft of Agricultural Science and Technology, edited by Liang Jiamian, Agricultural Press, 1989. )。 The climax of water conservancy construction in the south continued in the Song Dynasty, while the water conservancy construction in the north made little progress in the Song Dynasty due to natural and human factors, which opened the gap between the north and the south.

(6) Due to its strong national strength, the development of the southern region has been guaranteed. Generally speaking, compared with the Song Dynasty, the economy of the northern region in the Tang Dynasty was very developed and its comprehensive national strength was very strong, which created conditions for the further development of the southern region. Under this condition, the productivity of production tools has been obviously improved. Before the Tang Dynasty, the invention and improvement of farm tools were all around the cultivation and irrigation of dry land technology. Since the Tang Dynasty, due to the stereotypes of Jiangdong plough, paddy farm tools have been continuously developed, which has created conditions for rice planting and agricultural economic development in South China. With the popularization of rice planting, the land in the south became more mature and the paddy soil increased, and the agricultural economy in South China formed a virtuous circle, which made the national economy in the Tang Dynasty in an all-round development period.

The warm and humid climate created an environmental foundation for the development of agricultural economy in Tang Dynasty. According to research, the population of the Tang Dynasty was as high as 77.22 million, with more than 20 people per square kilometer. ) The cultivated land area ranges from 8 million to 8.5 million hectares. (Note: Wang Ji's Historical Draft of Sui and Tang Dynasties, China Social Sciences Press, 198 1 year. ) The population-land ratio is between 10 and 8. (Note: On the Relationship between Man and Land by Zhu Zhu, Fudan University Press, 1996. The ratio of people to land is between 8 and 10, which may be a reasonable index of traditional China society. In this sense, the development of civilization in the Tang Dynasty has the function of inheriting and accumulating the historical development of the previous generation. ) At that time, there was "within the four seas, the mountains are absolutely ravines, and the thunder is also full" (Note: Yuan Ci Shan Zhi, Volume 7, Wen Shi). ) Even the relatively arid Longyou area in the northwest was "moving in opposite directions, and Sang Ma was wild" in the early Tang Dynasty. (Note: Zi Jian (Volume 216). Economic development has created conditions for social development, so social development is known as "the road does not pick up the remains, the line does not enrich the grain" and "the journey of a thousand miles does not hold the edge". (Note: Tang Yulin, Volume III; "Tongdian" Volume 7. The development of material civilization has created conditions for political stability, military strength and cultural development. The achievements of the Tang Dynasty in imperial examinations, territory, literature, painting, music, sculpture, etc. had a great influence both in the history of China and in the world at that time, so the civilization of the Tang Dynasty became a page in the history of world civilization, which was based on the prosperous times of the Tang and Song Dynasties.

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1. During the Tang and Song Dynasties, the climate changed from warm to cold, and the nomadic people in the north went south.

According to Mr. Man Zhimin's research, the climate in the Tang Dynasty can be divided into two periods with the mid-8th century as the turning point. From the middle of 8th century to the middle of10th century, various cold events occurred frequently. In autumn, the cold air moves southward to raise the drought, but it is delayed in spring, and the earliest and latest frost and snowfall appear sooner or later. According to the research on the freezing phenomenon of rivers, lakes and seas, the climate zone is one latitude south than that of modern times. (Note: Man Zhimin's Study on the Stages and Characteristics of Climate Change in Tang Dynasty, Historical Geography, No.8). Zhu's research on the climate change in Guanzhong area also shows that the climate in Tang Dezong was mainly warm in winter and the temperature was high in the 7th and 8th centuries before Zhenyuan period (785-805). At the end of the Tang Dynasty, that is, in the 9th century after Zhenyuan, the winter was dominant, and frost and snow also harmed crops in the spring and autumn. This relatively cold period lasted until the Five Dynasties. (Note: Preliminary study on climate change in historical period in Guanzhong area of Zhu, Zhou and Zhou, Quaternary study 1998 1. Chen Jiaqi's research shows that the warmest climate in the past two thousand years was in the 7th and 8th centuries, that is, before the middle of the Tang Dynasty, but it was cold in the late Tang Dynasty and the Northern Song Dynasty. (Note: Chen Jiaqi et al. Study on Climate Change in Jiangsu in Recent Two Thousand Years. Geographical Science, No.3, 1998. Sheng Fuyao's research on Henan's historical climate also shows that it turned cold in the late Tang Dynasty. (Note: Sheng Fuyao's "A Preliminary Study on the Warmth and Warmth in Henan's Historical Period", Historical Geography, Series 7. ) Wen Huanran's "Schematic Diagram of Climate Change in China in 8000" also shows that the temperature was high before the middle of the 6th ~ 7th century, and then it began to drop to10th century. (Note: Wen Huanran's "Climate Change in Winter Half Year in China Historical Period", Science Press, 1996. According to Wang Zheng's research, from 880 to 1230, the climate was chaotic. After 880 years, the monsoon receded and the desertification in eastern China intensified. Generally speaking, it was relatively warm in the early period of 2000 and relatively cold in the later period. (Note: Wang Zheng et al. Influence of historical climate change on social development in China. Journal of Geography, No.4, 1996. In other words, the 300 years from 880 to 1230 is the transition period of climate change. But according to today's climate standards, it is still a relatively warm and humid period, which is what we call the medieval warm period. At the same time, we should also see that this period is a turning point from warm and humid to cold and dry, in which the mid-8th century and12nd century are two obvious abrupt periods in recent 300 years, and the abrupt change of12nd century should be larger in scale than that of the 8th century.

As early as the beginning of the 20th century, Huntington put forward this view in his book "E. Huntington, Puller in Asia", Boston, 1907.