What are the factors that affect the historical climate change in China?

Basic factors affecting weather changes in northern China.

The most significant decisive factor affecting temperature and rainfall is the "westerly belt". In the northern hemisphere, the westerly belt makes the wind move from west to east in the form of a belt. Due to the obstacle of mountains and the temperature difference between land and sea, the moving line of westerly belt is not parallel to latitude. The westerly belt reaches farther south in winter than in summer, and the cold wind in winter lowers the temperature. It's summer now, and the westerly belt of East Asia passes through central Mongolia and Manzhouli, and reaches Beijing and Hohhot in the south. In winter, the southern edge of the westerly belt can generally extend to Nanjing and Xiangyang. Due to the influence of warm ocean winds, the climate in coastal areas at the same latitude is milder than that in inland areas, and so are Japan and New England. Although we think this is "normal" now, compared with this century, the southern region where the westerly belt arrived was not always like this before this century.