The first cold period was from 1000 BC to 850 BC, that is, the cold period of the Western Zhou Dynasty. The Chronicle of Bamboo Records records the freezing of the Yangtze River and Hanshui River in the Zhou Dynasty, indicating that the climate at that time was colder than it is now.

The second cold period lasted from A.D. 1 century to A.D. 600, 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. In the early years of Emperor Jincheng, the Bohai Bay was completely frozen from Changli to Yingkou for three consecutive years. Horses and chariots and thousands of horses could drive on the ice, and the annual average temperature was 2-4℃ lower than it is now.

The third cold period is from 1000 to 1200, which is the Song Dynasty. During this period, Taihu Lake was completely frozen at11and opened to traffic by ice, 1 10.

The fourth cold period is from 1300 to 1900, that is, the severe cold period in Ming and Qing dynasties. During this period, Taihu Lake froze for several feet at 1329, and oranges froze to death. 1493 heavy snow fell in the Huaihe river basin from September of that year to February of the following year. Dongting Lake has become a "frozen land" with chariots and horses.

For 5,000 years, four warm periods and four cold periods have alternated in China, and the time difference is very obvious.

Alternating cold and warm is a natural phenomenon and law.