When did global warming first begin?

Warm winters have appeared more than once in human history. According to the isotopic changes of stalagmites, lake sediments, ice cores and other natural carriers and historical documents, since 6,543,800 years ago, the world has experienced two stages of warm winter: one is 3,500-6,000 years ago; Second, from 10 century to 13 century. During the Holocene Great Warm Period from 6,000 to 3,500 years ago, the annual average temperature of the earth was about 2 ~ 4℃ higher than it is now, which was generally warm all over the world, with frequent cooling in summer in Europe and continuous warm in winter in China. As a result, the growing season of plants is prolonged, the freezing point weather is shortened, and deciduous forests move northward. Such a climate has enriched human food, broadened the scope of activities and promoted the great development of Chinese culture and the great prosperity of the nation. It was at this time that the ancestors of the Yellow River, the Yangtze River and the Pearl River Basin flourished. Dating back to 30,000-40,000 years ago, it was another warm period. On a global scale, mankind has also ushered in a golden expansion period. Humans from North America, Australia and the Tibetan Plateau in China all migrated at that time.

The earliest recorded warm winter in China was when Dayu was in charge of water control. The temperature at that time was 2 ~ 3℃ higher than the average temperature in the last century. The second period, which experts call the "medieval warm period", took place from 900 to 1300, that is, the Tang and Song Dynasties in China. As early as 197 1, Mr. Zhu Kezhen, a famous scientist in China, drew a climate fluctuation curve in China in recent 5000 years according to the phenological records of China. In the picture, the temperature in the Tang Dynasty was about 1℃ higher than it is now, but when the Shang Dynasty was about to die, the temperature suddenly dropped. According to historical documents, Mr. Zhu Kezhen thought that the golden age of China feudal society-Sui and Tang Dynasties was a warm period in history. In the winter of 669 and 678, there was no ice and snow in Chang 'an, the capital of China. In the early 8th century and the early and middle 9th century, plum blossoms and oranges were planted in Xi 'an Palace and Quchi in the southern suburbs. The fruit of citrus in the Forbidden City in 75 1 year, and the fruit was recorded in 84 1 ~ 847 year. At that time, agriculture was abundant, the frontier was stable, and the people had not seen war for hundreds of years until the "An Shi Rebellion". The annual average temperature in the "medieval warm period" was 0.5 ~ 1℃ higher than it is now.

According to European literature, in the middle of14th century, there was an unexpected warm winter in northern Europe, and the harvest time of grapes and grains was advanced, and the traditional Oktoberfest was also advanced. Four tree ring width sequences in western Europe, which lasted for more than 1000 years, all revealed a warm period of about 250 years, during which alpine glaciers also retreated except warm spring and dry summer. However, climate warming is accompanied by drought, which some historians blame on the decline of the Silk Road. The arid climate swallowed up this prosperous passage along the valley water source, and some countries near the water disappeared.