China is a country with agriculture as the mainstay, and climate change has a direct impact on agricultural production in China. The climate change in China in the past 2000 years has a strong correlation with the rise and fall of dynasties. Generally, dynasties with stable society, developed economy, strong national strength and expanded territory of population growth will coincide with the warm climate period.

The chaotic years of the vassal state regime, peasant uprising and foreign invasion mostly belong to the cold period or cold period in China's history. In the history of China, the main foreign invasion was the nomadic invasion. During the cold and dry period, nomadic people in the north will face the threat of water grass depletion and ecological deterioration, so they will expand to agricultural areas. Moreover, the earlier the Central Plains Dynasty was established before the nomadic regime, the higher the possibility of being conquered by nomadic people.

At the beginning of each dynasty, because of the long-term war, the population was greatly reduced, the land resources were relatively rich, and the food supply was sufficient, so social stability and development could be maintained for a period of time. With the increase of population, the rewards of various factors of production gradually decreased, the food crisis led to the intensification of social contradictions, and the decline of dynasties followed.

After the war and famine, the population crisis disappeared and the new dynasty could go through the next cycle. In ancient China, due to the lack of industrial and commercial vitality and scientific and technological breakthroughs, agricultural society often fell into the Malthusian trap. When the linearly increasing means of subsistence cannot meet the exponential population growth, there will be poverty and war, thus forming the "periodic law of dynasties".

The Influence of Climate on Han Dynasty

Qin and Han dynasties were the first warm period in recorded history, when subtropical plants such as rice and bamboo forests could be planted in the Yellow River basin. According to "Historical Records", "Qilu Sang Ma has a thousand acres, and Weichuan Bamboo has a thousand acres". Sang Ma and bamboo, which are only found in the south today, can be planted in the Weihe River basin in Shandong and Shaanxi, indicating that the climate at that time was warmer than today. During the Qin dynasty, crops could be planted in the Taklimakan desert today, which is why the Qin dynasty was so powerful.

The warm period of the Han dynasty lasted, and after "cultural landscape management", the society was stable and there was no war in the frontier for many years. With years of accumulated material security, Emperor Wu of the Han Dynasty took the initiative to expel Xiongnu to West Asia and Eastern Europe.

During the reign of Emperor Guangwu of the Eastern Han Dynasty, Xiongnu suffered a rare locust plague, which was divided into southern Xiongnu and northern Xiongnu. In the twenty-sixth year of Jianwu in the Eastern Han Dynasty, the southern Xiongnu couldn't hold on any longer and asked for help from the Eastern Han Dynasty. After that, Emperor Guangwu subsidized 25,000 grains of grain and nearly 40,000 cattle and sheep in South Xiongnu.

From the first year of A.D., the whole earth ushered in the cold period of the Little Ice Age, which was a small period in the big period. With the return of the Southern Xiongnu and its southward migration, Dou Xian, a famous Eastern Han Dynasty soldier, attacked the Xiongnu twice and defeated the main force of the Xiongnu in Altai Mountain today. Then, he conquered more than 300,000 northern Huns, and Dahan completely defeated the Huns.

However, since the Western Han Dynasty proclaimed itself emperor for four years, the climate has entered a cold period, and there have been "snow in April, peach blossoms in autumn and plum blossoms". Moreover, the history of China entered the troubled times of the late Han, Wei, Jin, Southern and Northern Dynasties, which lasted for more than 300 years.

According to Zhu Kezhen's Climate Change in the History of China, during this cold period from north to south, that is, from the 4th century to the 5th century, the average temperature was 3 degrees Celsius lower than it is now. If the average temperature drops 1 celsius, the rainfall belt in China will move 200-300 kilometers south, and the rainfall will also decrease 100 mm ... at that time, it moved more than 500 kilometers south in Shanxi and Hebei.

As the rainfall moves south, it means that the agricultural area moves south, and the arable land area

Of course, the southward migration of a large number of Han people is also the main reason for the prosperity of Wudong and Han Shu. Wu Huan cavalry and other national armed forces are also important military forces that Cao Wei family can pacify the world.

The rise and fall of Tang dynasty

In 600 AD, during the Sui and Tang Dynasties, the climate in China ended the cold period of nearly 600 years and entered a warm period. During the Tianbao period of the Tang Dynasty, citrus and bamboo forests even grew in Chang 'an. Good climatic conditions have prolonged the planting time of crops, improved the multiple cropping index, increased the yield to varying degrees, and achieved rapid economic development.

However, since the 8th century, the climate in the north turned cold, and the winter wind made the climate in East Asia dry. According to "New Tang Book Five Elements", in the following 290 years, there were 75 droughts and more than 40 famines, almost once every two years and once every three years.

In the first year of Zhenguan, Emperor Taizong ordered the hungry to receive food free of charge in other states. During the Gaozong period, there were 12 droughts in 34 years, and even the phenomenon of "man eating man" appeared in Luoyang, the eastern capital. The long-term lack of rain has greatly hindered the water transportation, especially the food supply in Chang 'an. During the Tang dynasty, a large number of people moved south, which promoted the economic development of Jiangnan. Chang 'an is the political center and Yangzhou is the economic center.

Yangzhou is the distribution center of Jiangnan water transport. Materials are transported from Yangzhou to Chang 'an via Canal, Bianshui, Yellow River and Weihe River. In the Tang Dynasty, the winter wind was strong and the summer monsoon was weak, which led to simultaneous or alternate droughts in the Yellow River and Yangtze River basins.

In December of the first year of Ming Dynasty, Huang Chao entered Chang 'an, proclaimed himself the emperor and founded the country, and the Tang Dynasty continued. Years of drought have caused financial tension, which has triggered the competition for tax revenue between the central government and buffer towns. Buffer towns often intercept local taxes paid to the central government, which raises soldiers' self-esteem, resulting in a situation of "light inside and heavy outside" and greatly weakens centralization. According to historical records, when the Central Plains suffered a serious natural disaster, the chiefs of border ethnic minorities took advantage of the chaos to rob, kill and rob, and wantonly plunder.

The influence of climate in Qing dynasty

The temperature in Qing Dynasty was 1 to 2 degrees Celsius lower than today. In the Qing dynasty, where agriculture was underdeveloped, natural disasters caused by low temperature had a certain impact on society. Due to the introduction of sweet potatoes and corn in the Qing Dynasty, the population was more than that of the previous generation in most times, and even reached the highest of 440 million in the middle of the19th century.

The population growth was slow in the early Qing Dynasty and rapid in the Kanggan period. The whole growth continued until the Taiping Heavenly Kingdom broke out. After the invasion of the Taiping Heavenly Kingdom and other powers, the population decreased by 1/5, and it was not until the end of the Qing Dynasty that the population returned to its peak.

Compared with the previous dynasties, the population appreciation rate in Qing dynasty increased obviously. In the case of no major innovation in agricultural technology in Qing Dynasty, population expansion led to Malthus crisis. /kloc-since the 0/9th century, the climate in the Qing Dynasty has become cold and peasant uprisings have been frequent. Of course, famine was an important factor in the uprising.

Why does climate change lead to dynasty change?

In history, the nomadic people in the north were mainly animal husbandry, and the cold and dry climate was not conducive to agricultural production in the Yellow River basin, nor to the development of nomadic people. If the temperature drops by 2 degrees Celsius, the growth cycle of forage grass will be shortened by 40 days, resulting in a significant decrease in grass yield. Under the pressure of life, nomads must go south.

The Han people in the Central Plains, on the other hand, lost their national strength due to the decline in grain production. Coupled with the continuous peasant uprising, the internal friction caused by it also dried up the national treasury. Therefore, unable to resist the attack of nomadic people, they had to retreat to the south, so nomadic people invaded.

At the same time, the economic center of the Han area will also be affected by the climate. When the cold season comes, the focus of agriculture will move south, while the ethnic minorities in the south are relatively weak. When the first people moved to the south, there were fewer conflicts, and even more advanced planting techniques and advanced culture were brought to the south. For example, Yongjia Du Nan in Wei, Jin, Southern and Northern Dynasties not only established the Han regime, but even dominated the cultural direction.

During the Southern Song Dynasty, a large number of Han people moved into the Yangtze River valley, creating a rich land in the south of the Yangtze River, and the economy in the south gradually surpassed that in the north. On the surface, the southward movement of the economic center is the result of a large number of northern nomads invading and the southward movement of the political center. In essence, climate cooling is a potential driving force.

The peak of the number of wars in China usually occurs in the cold period, that is, when the weather is cold, there are more wars. From the end of Tang Dynasty to the end of Qing Dynasty, the peak of the Three Wars, the peasant uprising led by Zhu Yuanzhang at the end of Yuan Dynasty, the peasant uprising led by Li Zicheng at the end of Ming Dynasty and the invasion of Manchu Dynasty, and the peasant uprising of Taiping Heavenly Kingdom at the end of Qing Dynasty all occurred in the cold climate.

The cold climate affects the production of agriculture and animal husbandry, which leads to the shortage of production and living materials and often leads to wars. This is an inevitable choice made by people under the necessity of survival. The cold climate is often accompanied by drought, which leads to the decline of agricultural production level, land output, farmers' inability to pay taxes and social contradictions. When the contradiction is completely intensified, farmers rise up, nomads take advantage of it and a large-scale war breaks out.