Super thermal insulation performance
The basement wall and "roof" are hard soil, which makes heat transfer difficult, so the thermal insulation performance is super strong. This means that the temperature in the basement is always more stable than that outside, and the temperature difference does not change much.
It's colder in winter.
The basement is closer to the ground temperature, so it will feel colder in winter. But the basement has superior thermal insulation performance, so it is more stable than the outside world.
The hotter the weather?
The earth gets hotter as it goes down, but the basement is usually below average temperature, so it will feel cold in winter. Below the average temperature, the farther to the center of the earth, the higher the temperature.
Cave dwelling is the same principle.
Cave dwelling is also warm in winter and cool in summer, because it also has the characteristics of superior thermal insulation performance. Cave dwellings, like basements, are natural greenhouses.
Pay attention to ventilation and dryness.
Living in a damp basement for a long time is really bad for your health. So pay attention to keep warm and pay attention to ventilation and dryness.