Historical process of climate impact? How did the cold and humid weather promote the decline of the Tang Dynasty?

Comparing the development history of all countries in the world with the climate change in the world, you will find that the rise and fall of a country is usually linked to the climate, not only because of the direct influence of the climate, but also because of the causal effect brought by the climate change. In the Tang dynasty, it was precisely because the climate changed from warm to wet and cold in the middle and late period that nomadic people invaded and plundered the south. As a result, a series of changes took place, which eventually led to the decline of the Tang Dynasty. Since the farming era, the history of human civilization has been closely related to climate, and some major events in world history are often closely related to climate change. Although climate cannot determine the outcome of history, it can change the trajectory of history. Climate is one of the important factors that affect the historical process. Taking China as an example, the change of dynasties is often influenced by climatic factors that cannot be ignored. As the foundation of a country, agriculture is greatly restricted by climate, which can further affect the development of national strength. Climate often can't push the wheel of history through an instant change, but it can change the direction of historical process from long-term slow accumulation to subtle influence. The history of the rise and fall of the Tang Dynasty is an excellent proof. According to the comparison of a large number of documents and the changes of plant distribution, the climate was warm and humid before the mid-Tang Dynasty. Such climatic conditions led to the expansion of farming area in the Tang Dynasty, and formed a buffer zone for farming and grazing at the border of the Tang Dynasty. The expansion of agricultural areas will enhance the country's economic strength and make society more stable. On the other hand, the buffer zone on the border formed an effective local supply for the border areas of the Tang Dynasty, which eased the financial pressure of the country and made the military defense more stable. These conditions created a stable social environment for the economic development of the Tang Dynasty. However, after the middle of the Tang Dynasty, about the middle of the eighth century, the climate suddenly began to change from warm to cold, and cold events occurred frequently in various places. The cold air enters earlier in autumn, while the warm time in spring is later. After about the ninth century, the climate became colder, and even natural phenomena such as frost and snow destroyed crops in spring and autumn. At the same time, precipitation began to increase, leading to increased soil erosion, and even the Yellow River flooded many times. This caused the decline of the national strength of the Tang Dynasty, and the frequent floods in China made the Tang Dynasty exhausted. In this context, when various contradictions within the dynasty became acute, it undoubtedly weakened the ability to resist the nomadic people in the north. For the nomadic people in the north, the cold climate affects their living environment more. Nomads have been living on livestock, and the cold climate has led to the deterioration of grassland environment suitable for livestock growth, further squeezing the living space of nomads. In this context, nomadic people have to start to increase their efforts to go south under the pressure of survival. As mentioned earlier, the freezing weather led to the decline of domestic resistance in the Tang Dynasty, which led the Tang court to re-establish General Hu headed by An Lushan to suppress the invasion of nomadic people in the north. But what the Tang court didn't see was the hidden political ambition of An Lushan and others, and the Anshi Rebellion broke out, which was a landmark historical event of the Tang Dynasty's prosperity and decline, and the prosperity of the Tang Dynasty was gone forever. ?