Why did the temperature in the north and south of Song Dynasty generally get cold?

The third cold period was from the second year of Emperor Taizong in the Northern Song Dynasty to the third year of Shaoxi in Song Guangzong.

Since the second year of Emperor Taizong of the Northern Song Dynasty (AD 985), the climate has taken a sharp turn for the worse, and the strange cold scene with snow and ice all over the Jianghuai area has reappeared. The third Little Ice Age invaded China for 5,000 years. After the Tang Dynasty, all the citrus and other fruit trees that could be planted in Chang 'an and Luoyang froze to death, while the Huaihe River basin, Jiangnan, the lower reaches of the Yangtze River and Taihu Lake were completely frozen, and horses and chariots could pass through the frozen rivers. Look at the following climate records, the distribution of animals and plants, and the geographical landscape to know the degree of cold climate in China after the middle period of Taizong in the Northern Song Dynasty.

◎ Climate record and pollen fossil research: In the winter of the second year of Emperor Taizong, Nankang Jun said: Heavy rain and heavy snow, rivers and rivers are frozen together, and horses and chariots can bear heavy loads. In September of the first year of Chunhua in the Northern Song Dynasty (AD 990), Miao was injured by heavy snow in Beijing. In the winter of the third year of Emperor Taizong's reign (AD 997), it was raining and snowing in the south of the Yangtze River, and the Yangtze River was frozen. On the volume of Yanbei Magazine: Dongting Lake is an orange industry, and its income is similar to that of farmers. In Song and Yuan Dynasties (1 1 1), it snowed heavily in winter, the river was completely frozen, and all oranges froze to death. In the Ming dynasty, it was paid logging. In April of the first year of Qin Zongjingkang (BC 1 126), it was raining heavily in Beijing and the weather was cold. From May to June, heavy rains hurt wheat, and summer comes to autumn. In the first month of the second year of Jingkang, it was snowing heavily and freezing. Ice is like a mirror, and the walker can't stand. Many people froze to death. In April, the north wind in my heart is very cold. At that time, there were more than 600 kinds of frozen local chronicles recorded in Dongting Lake and Poyang Lake in the Yangtze River Basin, Huaihe River Basin, Jiangnan and other places, which were wonders of ice and snow. As far as we know, the Yangtze River and Huaihe River will not freeze today. Coupled with scientists' research on pollen fossils, it is estimated that the temperature at that time was about 1.0- 1.5 degrees Celsius lower than it is now. In the article History and Climate Change in China, Zhu's Lotus Boat recorded 45 snowfalls in late spring in Hangzhou in the first year of Southern Song Dynasty (1131-1264)133. If compared with the last snowfall in Hangzhou today, it was frozen in the early Southern Song Dynasty. As for the situation of the least drought and the most precipitation in the Southern Song Dynasty, Zhu thinks it may be related to the southward tropical cyclone and the increase of sunspots.

◎ Distribution of animals and plants. At the beginning of the Northern Song Dynasty, tropical animal elephants, which were originally active in Kaifeng, Henan and Central China, gradually moved southward because of the cold climate. After the end of the Northern Song Dynasty, elephants no longer existed in the Central Plains and the Yangtze River valley, but only existed in the south of China. Rice needs a warm and rainy environment to grow. Before the Han Dynasty, the Yellow River valley in China was warm and rainy, and there was rice production. But after the Eastern Han Dynasty, the weather became cold, and the rice in the Yellow River valley became less and less. In the Song Dynasty, the rice yield in the north was even less. There is little rice except upland rice. It can be seen that the cold weather in ancient times made rice no longer grow. In the Southern Song Dynasty, Zhu Yitang commented on the Book of Songs: "Rice, the rice eaten by southerners, is aquatic and white in color." If there had been rice cultivation in the north at that time, Zhu would not have made such comments. Like rice, bamboo needs a high temperature and rainy environment. Before the Han Dynasty, there were many bamboos in the north, which were widely distributed. However, with the decrease of temperature, the output of bamboo gradually decreases. After the end of the Northern Song Dynasty, the output was even less. In Meng Xi's written conversation, he mentioned that "there is no bamboo in Yan Jun" and "bamboo is not a local product". It can be seen that there were few bamboos in northern China at that time, which should also be the cause of climate change.

◎ Geographical landscape changes. According to the literature, during the Southern Song Dynasty, the mountainous areas of Siramunor and Ilam in Xinjiang were covered with ice and snow all the year round, but today it is a green grassland, which shows that the climate in the Southern Song Dynasty was even colder than today.