Why is it getting colder and colder?

The earth passed the "summer solstice" in its orbit. On the ground in the northern hemisphere, the sun seems to move southward day by day, especially after the "autumnal equinox". In this way, sunlight is more and more inclined to the northern hemisphere, and the heat received by sunlight per unit area is gradually reduced, and the surface temperature is getting lower and lower, so the temperature is getting lower and lower. It's getting colder and colder.