Why did it suddenly get cold?

The formation of the four seasons is mainly due to the oblique intersection of the equator and the ecliptic (the path taken by the sun as seen on the earth). When the earth moves, its axis remains the same in the direction of space. In winter, the sun shines obliquely on the ground, and each unit area on the ground is less heated. In addition, the daytime is short, and the time for receiving sunlight every day is short, that is, the heating time is short. Then because of the atmosphere around the earth, it absorbs some light and heat. When light is irradiated, the thicker it passes through the atmosphere, the more it is absorbed, resulting in cold in winter. In summer, the sun shines directly on the ground, the days are long and the light passes through the atmosphere very thin, so the climate is hot. In the spring and autumn rainy season, it lives between winter and summer, so the climate is mild. It is because in winter, the height angle of the sun is small, the sun shines obliquely on the earth, the energy density of solar energy reaching the earth is small, and the earth gets less energy from the sun, so it is cold in winter; In summer, the height of the sun is high, and the sun shines almost directly on the earth. The energy density of solar energy reaching the earth is high, and the earth gets more energy from the sun, so it is hot in summer. Because the revolution of the earth around the sun is an ellipse, in winter, our earth is closer to the sun; In summer, our earth is far from the sun.