From the late Quaternary Pleistocene, about 1. 1, 000 years ago, the earth entered the modern interglacial period, also known as the post-glacial period, from the latest sub-glacial period of the Quaternary Glaciation. This period of time is roughly equivalent to the fact that mankind has entered a historical era with written records. With regard to the climate in this period, Norwegian glaciologists have made a snow line fluctuation map of nearly 10000 years, which shows that the snow line fluctuates greatly, indicating that the climate has changed obviously since the late glacial period. China has a long history. Zhu Kezhen sorted out and analyzed these records, and found that the climate in China for more than 5,000 years has four warm periods and four cold periods.
The first warm period was from 3000 BC to 1000 BC, that is, from Yangshao Culture Age to Anyang Yin Ruins Age. In most of this period, the annual average temperature was about 2℃ higher than it is now, and the temperature in Leng Yue was about 3℃-5℃ higher than it is now.
From about 1000 BC to 850 BC (the beginning of the week), there was a short cold period, and the annual average temperature was below 0℃.
From 770 BC to the early AD, that is, the Qin and Han Dynasties, it entered a new warm period.
From the early years of AD to AD 600, that is, the Eastern Han Dynasty, the Three Kingdoms and the Six Dynasties, entered the second cold period.
The period from 600 AD to 1000 AD, namely the Sui and Tang Dynasties, was the third warm period.
1000 to 1200, that is, the southern song dynasty was the third cold period, and the temperature was about l℃ lower than that of modern times.
The period from 1200 to 1300, that is, the end of the Song Dynasty and the beginning of the Yuan Dynasty, was the fourth warm period, but this time it was not as warm as that in the Sui and Tang Dynasties, showing that the northern limit of elephant survival gradually moved from the Huaihe River basin to the south of the Yangtze River basin, such as Zhejiang, Guangdong and Yunnan.
After 1300 years, that is, since the Ming and Qing dynasties, it was the fourth cold period, and the temperature was 1-2℃ lower than that of modern times.
In the past 5000 years, although cold periods and warm periods appeared alternately, the general trend was from warm to cold, and each cold period was longer and colder. During the second cold period, only the Huaihe River froze in 225 AD. 1670 During the fourth cold period, the Yangtze River was almost frozen.
Interestingly, Norwegian glaciologists use the height of the snow line to indicate the rise and fall of the temperature, while Zhu Ke uses historical documents to record the data, but the results are very consistent, indicating that the climate change since the late ice age is universal all over the world, which is definitely not a coincidence.
1973, Zhu Kezhen put forward the basic situation of periodic climate fluctuation in China. He believes that in the past 2000a years, the Han Dynasty was a warm period, and soon after the Three Kingdoms began, the climate became cold, which delayed the beginning of the Tang Dynasty. After the end of the Tang Dynasty, the climate became cold again, and gradually entered the Little Ice Age in the15th century, showing a structure of two peaks and three valleys, until the climate became warmer in the early 20th century and the Little Ice Age ended. The Han Dynasty and the Tang Dynasty were warm periods when the annual average temperature was about 2℃ higher than that of modern times. The research results have been widely used in climatology and historical geography. But in recent years, due to the discovery of new materials and the improvement of research methods, many scholars have supplemented Zhu Kezhen's work. Among them, Zhu and others believe that since 2000 ~ 3000, the climate change in China has gone through the following stages: ① the cold and dry climate in the Western Zhou Dynasty (BC 165438 to the middle of the 8th century BC); ② Warm and humid climate from the Spring and Autumn Period to the early Western Han Dynasty (from the middle of the 8th century BC to BC 1 century BC); ③ The cool and dry climate from the late Western Han Dynasty to the Northern Dynasty (65438 BC+the middle of the 0 th century to the 6 th century); ④ Warm and humid climate in Sui and pre-Tang period (7th-8th century); ⑤ The cool and dry climate from the late Tang Dynasty to the Northern Song Dynasty (9 ~ 1 1 century); ⑥ The dry and wet climate in the early Jin Dynasty (12nd century); ⑦ The cool and dry climate at the end of Jin and the beginning of Yuan (13 and the first half of 65438+4th century); ⑧ During the Ming and Qing Dynasties (1the second half of the 4th century to the beginning of the 20th century), the climate was cold and dry. Later, many geographers made further amendments to the climate change in China, but the trend was generally the same.
In the historical period, the climate not only fluctuates periodically in temperature, causing temperature changes, but also changes in humidity. Generally speaking, warm period and wet period, cold period and dry period are corresponding, but each cold and warm period has wet and dry fluctuations, which cannot be generalized. Zhu and others believe that the change of temperature is faster than that of precipitation, and the change of precipitation is greater than that of temperature. In the historical period, the fluctuation of climate change of temperature and humidity has obvious correlation, but they are not completely synchronized.
Human beings affect the climate, and the climate also affects human beings. Short-term climate change, especially extreme abnormal climate phenomena, such as drought, flood, freezing injury, hail and sandstorm, often leads to serious natural disasters, which is enough to bring devastating blows to human society. For example, the rainstorm disaster in Bangladesh in 1943- 1954 caused the biggest famine in the 20th century, and 30,000-40,000 people starved to death. 1968-1973 The drought in Africa is a great disaster for the African people. It has caused 70-90% livestock losses in Chad, Niger and Ethiopia, and 200,000 people have starved to death in Wolo province of Ethiopia alone. Of course, such attacks are often short-lived and partial. Although it will not affect the ecosystem, it will cause great disasters to mankind.
Long-term climate change, even if the change is slow, will fundamentally change the ecosystem and completely change the production layout and mode, thus affecting the economic life of human society.
For example, during the warm period of 3000- 1000 BC, bamboo was widely distributed in the Yellow River basin to the eastern coast; There are tropical and subtropical animals such as buffalo and wild boar found in Yin Ruins in Anyang. Oracle Bone Inscriptions recorded that he got an elephant while hunting, indicating that the elephant fossils in Yin Ruins are native. Henan, formerly known as Yuzhou, is a symbol of people holding elephants. In Shang and Zhou dynasties, plums were an important daily food for northerners. The Book of Songs says: "If you make soup with salt, you will only appreciate plums." It can be seen that plums were as important as salt at that time and were an indispensable seasoning for cooking. The Book of Songs says: "When the moon comes to the south, there are rules and regulations." . Zhong Nanshan is in the south of Xi, and there have been no plum blossoms since the Song Dynasty. People in Shaanxi and Shanxi have to use vinegar instead of plums.
The climate in Qin and Han dynasties was also warmer. According to historical records, the geographical distribution of cash crops at that time was "the orange in Jiangling, the mulberry in Qilu, the bamboo in Weichuan and the paint in Chen Xia". It can be seen that the boundary of subtropical plants at that time was farther north than it is now.
Because climate change directly affects the geographical distribution of crops, it will inevitably affect the industrial layout with agricultural products as raw materials. For example, from the pre-Qin Dynasty to the Western Han Dynasty, the layout of China silk industry was north silk and south hemp, and most of the silk industry was in the middle and lower reaches of the Yellow River and the Central Plains of Hebei Province. At that time, the largest silk industry center was in Dingxian County, Hebei Province, and other smaller centers were also in Hebei, Henan and Shandong. Hemp fabrics are mainly produced in the Yangtze River valley and the southern region. During the Western Han Dynasty, Shu was only famous for producing flax. Although from the Eastern Han Dynasty to the Wei and Jin Dynasties, there were frequent wars in the Central Plains, the economy declined sharply, the social life in the southern region was relatively stable, and the silk weaving industry was developed, but until the Sui and Tang Dynasties, the layout of northern silk and southern linen was maintained. From the perspective of climate change, during the Sui and Tang Dynasties, although the climate also changed, the average temperature was still warmer than that in modern times, indicating that the Silk Road appeared in the north for a reason.
The change of the layout of North Silk and South Hemp occurred in the Song Dynasty. Due to the cold climate, the temperature has been lower than that in modern times, which is not conducive to the production and reproduction of silkworm in the north. Coupled with the war in the north in the late Tang Dynasty and the Five Dynasties, the economy in the south rose, and the scale of silk weaving industry gradually surpassed that in the north. During the Northern Song Dynasty, Zhenjiang and Santai had become the national silk industry centers. During the Southern Song Dynasty, Nanjing, Changzhou, Zhenjiang and Suzhou all had huge silk production capacity. The shift of the center of gravity of the silk industry to the south coincided with the period when the climate in China changed from warm to cold. This historical experience is worth learning.
Climate change also affects agricultural cultivation. Mencius (372- 289 BC) and Xunzi (365,438+03-238 BC) both said that agricultural planting in Qi and Lu (Hebei and Shandong) could be harvested twice a year. Until the early days of liberation, these places were only used to two years and three crops. The growing season in the Tang Dynasty was also longer than now. Schumann (written about 862) said that in the south of Qujing and the west of Dianchi Lake, two crops are harvested a year, rice in September and wheat or barley in April. In modern times, due to the shortened growing season, peas and broad beans have to be planted instead of wheat and barley. This historical experience is still of practical significance today. For example, if the climate is warming, we can consider the expansion of double-cropping rice to high latitudes and high altitudes; If the climate gets cold, measures must be taken to shorten the growth time of rice.
First, the time difference
Climate includes two basic elements: temperature and dry and wet conditions, and the study of historical climate must also start from these two aspects. The article "Preliminary Study on Climate Change in China in the Last Five Thousand Years" by the famous scientist Mr. Zhu Kezhen (①) systematically summarizes the basic laws of climate change in China, indicating that the temperature change in China in the last five thousand years has four warm periods and four cold periods.
1. The first warm period was from 3000 BC to 1 100 BC, that is, from Yangshao culture period to Yin and Shang dynasties. Oracle Bone Inscriptions recorded that Anyang rice was planted in February of the lunar calendar, more than a month earlier than now. The analysis of the peat layer near Beijing shows that a large number of broad-leaved forests grew there 5,000 years ago, representing a fairly mild climate.
2. The first cold period was from 1000 BC to 850 BC, that is, the cold period of the Western Zhou Dynasty. Chronicle of Bamboo Slips records the freezing of the Yangtze River and Hanshui River in the Zhou Dynasty, indicating that the climate at that time was colder than now.
3. The second warm period is from 770 BC to the beginning of AD, that is, from the Eastern Zhou Dynasty to the Qin and Han Dynasties. There are many records in Chunqiu about Lu's "no ice in the first month of spring", "no ice in February of spring" and "no ice in spring". Xun Guo Pian and Mencius Shang recorded that agriculture planted crops twice a year in Qilu area.
4. The second cold period lasted from 1 century to 600 AD, that is, the cold period of the Eastern Han Dynasty and the Southern and Northern Dynasties, and reached its peak in the first half of the 4th century AD. According to Zi Tongzhi Bamboo Slips, in the early years of Jincheng, Bohai Bay was completely frozen from Changli to Yingkou for three consecutive years. Cars, horses and thousands of troops can travel on the ice, and the annual average temperature is 2-4℃ lower than it is now.
5. The third warm period is from 600 AD to 1000 AD, that is, the Sui and Tang Dynasties. During this period, there was no ice and snow in the winters of 650 AD, 689 AD and 678 AD, and the climate was warm and visible.
6. The third cold period is from 1000 to 1200, which is the Song Dynasty. During this period, Taihu Lake11was completely frozen and opened to traffic on ice, 1 165438.
7. The fourth warm period is 1200 ~ 1300, that is, the warm period in the late Song Dynasty and early Yuan Dynasty. 1225, Taoist Qiu Chuji wrote a poem "Spring Tour" in Changchun Palace, Beijing: "During the Qingming Festival, apricot blossoms bloom, and thousands of families come to work every day." This shows that the climate in Beijing was warmer then than it is now.
8. The fourth cold period is 1300 ~ 1900, which is a severe cold period in Ming and Qing Dynasties. During this period, Taihu Lake was frozen several feet thick at 1329, and oranges froze to death. During the period of 1493, heavy snow fell in the Huaihe River basin, which stopped in September of that year and ended in February of the following year. Dongting Lake has become a "frozen land", with cars and horses coming and going.
For 5,000 years, four warm periods and four cold periods have alternated in China, and the time difference is very obvious.
Second, the spatial differences.
There are four factors affecting climate change in historical period: solar radiation, underlying surface, atmospheric circulation and human activities. The interaction of these factors determines the climate change, and the latitude position, land and sea position, vast area, complex terrain and circulation factors that dominate the climate in China determine another feature of climate change in China-the emergence of spatial differences.
The climate fluctuation on the earth is first related to the intensity of solar radiation. The cycle of spring, summer, autumn and winter, and the difference between cold, warm and hot areas are all due to the different intensity of solar radiation. China's territory starts from the center of Heilongjiang in the north, reaches Zengmu shoal in the south, and spans 49 latitudes from north to south. From south to north, it is divided into six hot zones: equatorial belt, tropical zone, subtropical zone, warm temperate zone, temperate zone and cold temperate zone, among which temperate zone, warm temperate zone and subtropical zone have the widest area, which is the basic factor to determine the diversity of climate types and the spatial difference of climate change.
From the land and sea position, China is located between Asia and Europe, the largest continent in the world, and the Pacific Ocean, the largest ocean. Due to different surface heat conditions, different temperature and pressure fields are formed, which leads to obvious monsoon circulation and has a far-reaching impact on China's climate. Compared with the same latitude regions in the world, the Yellow River Basin in China is equivalent to the Mediterranean region, and the latitude south of the Yangtze River is equivalent to sub-Saharan Africa in North Africa. According to the law of planetary wind system, Jiangnan in China belongs to desert, but due to the subtropical monsoon climate, the eastern and southern regions of China have high temperature and high precipitation, making them unique regions with the richest subtropical natural resources in the world.
From the east-west trend of China's three mountain systems, as a barrier of cold and warm air flow between north and south, they also constitute an important climate dividing line. Among them, the Qinling Mountains with an altitude of1500-2500m have the most obvious influence. The northern part of Qinling Mountains is warm temperate zone and the southern part is subtropical zone. The so-called poem "The mountains bloom first in October, and the south branch is warm in the north and cold in the north" just shows that Qinling Mountain is the dividing line between the north and south climate in China. The Qinghai-Tibet Plateau above 5000m above sea level can't get the humid climate of the Pacific Ocean, and the water vapor channel from the Indian Ocean is cut off by the Himalayas, making the northwest inland of China a desert arid climate. In addition, the Siberian cold air explosively invaded from the Mongolian Plateau to the south, forming a strong cold wave that affected most parts of northern China in winter, which increased the spatial difference of climate change in the east, west, north and south.
In China, the climate is getting colder from south to north and from east to west, and forests, grasslands, barren sand and deserts also appear in turn, thus forming a completely different climate from east to west, north and south. The biggest feature is the natural differentiation of climate in the southeast and northwest. The spatial and temporal differences of climate change alternate, which has a great impact on the historical development of China in different periods.
Third, the influence of time and space differences.
The first is political influence.
The division between the southeast and northwest of China caused by the difference of climate in time and space has had a far-reaching impact on the social development of China. Modern geographers draw a diagonal line on the map of China from Heihe River in Heilongjiang Province to Tengchong in Yunnan Province. The northwest of China is in the west and north of the diagonal line, accounting for 57. 1% of the territory of China and 5.6% of the total population. It is generally the main activity area of nomadic people or ethnic minorities in history. To the east and south of the diagonal is the southeast of China, occupying 42% of the territory and 94% of the total population. It is basically the main activity area of agricultural nationalities (Han nationality) in history. (2) Among them, with the change of climate, the economy and culture in the southeast gradually surpass that in the north, and the population density is increasing.
Between the northwest and southeast of China, the ancient Great Wall is generally consistent with the natural dividing line of agricultural and pastoral areas. As early as 1 12 1 years ago, road flyover Qiu Chuji said when crossing Yehuling, the first pass in Zhangjiakou in the north, "Climb high and look far, overlooking Taihang Mountain. It's sunny and lovely. In the north, the cold sand declined, and the wind of the Central Plains was isolated from then on. " "Liao History Wei Yingzhi" also said: "The south of the Great Wall is rainy and hot, its people plow for food, Sang Ma is clothed, the palace is inhabited, and the city walls are governed; Between the deserts, it's cold and windy. Animal husbandry feeds on fish, fur and clothes, and converts to disciples at any time to make chariots and horses. This time and place is limited to the north and the south. " This geographical environment determines the confrontation between agriculture, animal husbandry and agricultural nationalities and nomadic nationalities in the history of China, and the two economic nationalities both communicate peacefully and wait for each other. Whenever the cold period replaces the warm period, there are always large-scale nomadic people migrating to the warm areas in the south, and the agricultural dynasty in the Central Plains is facing the challenge from the nomadic people in the north. Among them, the "Five Wild Flowers" around 400 AD, the Khitan, the Nuzhen and the Mongols went south one after another around 1200 AD, and the Manchu entered the customs around 1700 AD, which is the most typical example of the military conflict between the farming and pastoral peoples. The war and relationship between the Central Plains Dynasty and the northern minority regimes has always been the key factor that affects and restricts the social and historical development of China.
The confrontation between agriculture, animal husbandry and ethnic groups has the most direct influence on politics. With several biggest military conflicts, there have been several typical political situations of confrontation between the Northern and Southern Dynasties. Accompanied by the "five disorderly flowers" was the first Northern and Southern Dynasties-the confrontation between the sixteen northern countries and the Northern Wei Dynasty, the Northern Qi Dynasty, the Northern Zhou Dynasty and the Southern Eastern Jin Dynasty, the Song Dynasty, the Qi Dynasty, the Liang Dynasty and Chen Dynasty; Along with the southward migration of Khitan, Nuzhen and Mongolia, it was the second confrontation between the Southern and Northern Dynasties and the Liao, Jin and Song regimes. In the Ming Dynasty, the regime in the early Ming Dynasty confronted the regime in the Northern Yuan Dynasty. Then there is the confrontation between the Nanming regime and the Qing regime in the late Ming Dynasty. Due to the long-term confrontation between the North and the South, the agricultural people have to rely on the centralized central government to organize scattered farmers to build the Great Wall of Wan Li to defend their lives and meet their needs, which is one of the important reasons for the long-term existence of centralized system in China.
The second is the economic impact.
Five or six thousand years ago, at the same time as the warm period, it was a rather humid climate. At that time, the Heilongjiang River Basin was the wettest period for thousands of years, and the Beijing Plain was the hometown of rivers and ponds. About 2500 years ago, the climate became dry. During the archaeological excavation in Beijing, it was found that the peat bog representing the humid climate gradually disappeared. About 1000 years ago, the climate became dry again. According to a large number of records of droughts and floods in local chronicles, since the beginning of A.D., floods in southeast China have decreased relatively, while droughts have increased relatively, with A.D. 1000 as the boundary. The last dry period 1000 was short and the wet period was long. After that, the wet period is short and the dry period is long. The chronology of drought and flood data in recent 500 years shows that drought is obviously more than flood.
The change of dry and wet climate has great influence on agricultural production. It goes without saying that agricultural production in arid and cold regions is severely restricted. In other areas, the changes of cold, warm, dry and wet climate also affect the development of agricultural production. Generally speaking, every time the temperature drops by 65438 0℃, the position of the northern boundary of the subtropical zone will move south by about one latitude, and the position of the northern boundary suitable for crop growth will also move south. In recent 5,000 years, the general trend of climate fluctuation in China is that the warm period becomes shorter and the warmth becomes lower, which determines the general trend that the economic center of gravity, which is dominated by agricultural economy, moves southward. In the history of China, the economic center of gravity moved southward mainly in three periods: during the Wei, Jin, Southern and Northern Dynasties, the economy of the Yellow River basin stagnated and declined, the Yangtze River basin was greatly developed, and the economy of the South rose; During the Five Dynasties and the Song Dynasty, the southern economy rose and surpassed the northern economy, forming a new economic center of gravity, and the economic situation of "prosperity in the south and decline in the north" continued to develop; Since the Ming and Qing dynasties, the economic center of gravity has moved further south, the southeast coastal areas have developed abnormally, and the gap between the east and the west and the gap between the north and the south has further widened. Looking at these three large-scale economic movements to the south, it coincides with the arrival of the second, third and fourth cold periods in history, from which it is not difficult to see the relationship between geographical environment and economic development.
The third is the influence of culture.
Economy is the foundation, and its change determines the change of superstructure. With the shift of economic center of gravity to the south, it will inevitably lead to great changes in superstructure culture. The most obvious manifestations are: before Sui and Tang Dynasties, the economic center of China was in the north, and the cultural center was also in the north; After the Sui and Tang Dynasties, the economic center of gravity moved south, and the cultural center moved south accordingly.
During the Qin and Han Dynasties, Guanzhong was the capital, and the economic and cultural center of gravity was in the Yellow River basin. There is a saying that "Shandong is the leader, Shanxi is the leader", "Kansai is the leader and Kanto is the leader". After the Sui and Tang Dynasties, food supply began to depend on the south, and the cultural center of gravity also began to migrate to the south. In the Song Dynasty, there was a saying that "Su Changshu is the best in the world" and "Jiangsu and Zhejiang are familiar with each other and the best in the world". In the Ming and Qing dynasties, there was a saying that "the lake is wide and ripe, and the world is enough". At this time, China's culture was based on the richest Yangtze River valley, forming a situation that "the southeast is rich and Jiangsu and Zhejiang are humanities". Since modern times, with the development of coastal economy, Guangdong and Fujian have gradually occupied an important position in the economy, and China culture has a tendency to move further south.
As for the shift of China's cultural center of gravity to the south, predecessors mostly studied it from the aspect of "the geographical distribution of historical figures in China". Here are two schools of thought to illustrate the relationship between culture and geographical environment. In the article "The Relationship between Historical Figures and Geography" (③), Ding Wenjiang made a list of provinces according to the figures of the four dynasties of Han, Tang, Song and Ming in the Twenty-four History:
Before Han Dynasty, after Han Dynasty, Tang Dynasty, Northern Song Dynasty, Southern Song Dynasty, Ming Dynasty
The provinces with the largest population are Shandong, Henan, Shaanxi, Henan, Zhejiang and Zhejiang.
Henan, Shaanxi, Hebei, Fujian and Jiangsu
Japanese Sang Yuan collected in the article "Observing the North and South Cultures of China from History" [④], taking the imperial examination as an example, and submitted the statistics of the number of people who passed the examination in Ming and Qing Dynasties. From the fourth year of Hongwu in Ming Dynasty to the forty-fourth year of Wanli, there were 244 subjects, including 2 15 in the south, accounting for 88%, and 29 in the north. In the eighteenth year of Emperor Kangxi of Qing Dynasty, 50 students were enrolled, including 42 from the south. In the first year of Qianlong, students 15, and the south accounted for 14. There were 203 top scholars in the Ming and Qing Dynasties, and there were 188 in the south.
Four. Discussion on related issues
1. Through the above discussion on the characteristics and impacts of climate change in China, we can further understand the role of geographical environment in historical development. How to treat the relationship between geographical environment and historical development is an old and often new topic. In the past, due to the one-sided criticism of "geographical environment determinism", the role of geographical environment in historical development was rarely discussed in detail. In recent years, through various aspects of research and discussion, people realize that the geographical environment itself is a part of human society and its historical development. When transforming the natural environment, human beings should not violate the constraints of natural laws, otherwise they will be punished by natural laws. But what is the relationship between geographical environment and the development of human society? What influence does the geographical environment have on the development of social history? How great will the impact be? There are still different opinions on these issues. Through the analysis of this paper, it can be affirmed that the influence of geographical environment on social history is a historical category, and its mode and degree of action are constantly changing with the evolution of the times. Therefore, we should attach importance to the study and research of historical geography. In the study of China history, why is the feudal society in China particularly long? Why is the embryonic development of capitalism extremely slow? Many comrades believe that geographical conditions are the most fundamental factor. Specifically, China's internal and external geographical environment and the characteristics of its corresponding social production mode not only produced the demand for authoritarian regime, but also maintained the prosperity of feudal small agriculture, making it difficult for China to have the objective conditions for the transition to capitalism, thus leading to the long-term continuation of China's feudal society. Are these views correct or not? We need to thoroughly study the history and geography of China before we can draw a conclusion.
Secondly, through the above analysis, we also realize that human history and geographical environment are a unity, which restrict and interact with each other. This kind of mutual restriction and interaction shows different forms at different times and in different regions. Generally speaking, the lower the level of productivity, the greater the restriction of human beings by geographical environment; The older the stage of social development, the greater the dependence of human beings on the geographical environment. In ancient China, the temporal and spatial differences of climate change influenced the development direction of politics, economy and culture, indicating that the geographical environment really promoted or delayed the history of China. Especially in the history of China, several confrontations between minority regimes and Han regimes (Qin and Han Dynasties and Xiongnu, Eastern Jin and Southern Dynasties and Wuhu, Song, Liao, Jin, Ming and Meng, Manchu and so on). ) are all environmental factors of confrontation between farming and pastoral areas caused by climate differences in time and space. With the development of social productive forces, especially the progress of science and technology, human society has increasingly restricted the geographical environment that can provide more material wealth for human beings. However, this does not mean that the role of geographical environment is reduced. Due to the influence of human beings on the geographical environment, the geographical environment has changed and formed a new geographical environment system. In addition to the original natural environment, the economic environment and human environment system have been added, which has had a new impact on human society. In the modern climate change in China, we have to explore the new changes and new influences of human environmental pollution, which determines the guiding significance of studying historical geography to reality and practice.
2. By discussing the characteristics of climate change in China's history, we can further understand the disciplinary nature of historical geography. Historical geography is an ancient and young discipline, and there are different views on its nature in academic circles. At present, the history department and some geography departments of domestic universities have set up the course "Historical Geography of China", but the teaching content, learning focus and research direction are quite inconsistent due to different views on its subject attributes. Some people regard it as a branch of history, focusing on the study of evolutionary geography; Some people regard it as a branch of geography, emphasizing the discussion of natural phenomena and their laws in historical periods; Some people regard it as an interdisciplinary subject of history and geography, focusing on interdisciplinary research.
We believe that historical geography is not only an interdisciplinary subject between history and geography, but also an interdisciplinary and interrelated comprehensive subject between many disciplines in natural science and social science. Historical geography not only studies the natural process of natural environment change, but also studies the man-made process of transforming natural environment change. More importantly, it focuses on the changing law of the relationship between man and land in historical period. Therefore, it can not be simply attributed to a branch of history or geography, but a new interdisciplinary system. As Zhekulin, a historical geographer in the former Soviet Union, said, it is not only a marginal discipline formed by the combination of geography and history, but also "closely related to a series of scientific categories such as ethnography, toponymy and agricultural history" in its own development process. Therefore, accurately speaking, it is "a comprehensive discipline on the edge of natural science and social science, and its main task is to study the regularity of social and natural's interaction." ⑤ Based on this understanding, our horizon of historical geography research will be gradually broadened.
The nature of the discipline determines the research methods of the discipline. The world is a whole, and nature and human society are inseparable. Modern science and technology have reached the stage of mutual penetration and integration among disciplines, and historical geography has emerged to meet the requirements of this era. Therefore, it inevitably requires us to master the knowledge of different disciplines and conduct creative research on the basis of the cross-study of social science and natural science. This paper analyzes that if we can play a role in this respect, the purpose will be achieved.