Of course Earth's core is very hot. So below the permafrost, the temperature very slowly increases toward that hot core. It typically rises about one degree for every 70 feet deeper we go. The active layer above the permafrost takes different forms.

The Earth begins to get noticeably warmer than the surface air at a very shallow depth, but the "geothermal gradient" becomes consistent after about 10 to 20 meters (33–66 ft). Above this point, the ground temperature is influenced by local weather and seasons. Once you descend past 20 meters, the temperature stays at a stable "mean annual ground temperature." As you go deeper into the crust, the temperature rises at an average rate of 25°C to 30°C per kilometer (about 72–87°F per mile). This means that in a deep mine or borehole, it can feel sweltering just 1–2 miles down. By the time you reach 100 km deep, the temperature is roughly 1000°C. In 2026, this consistent heat is increasingly being harnessed for "deep geothermal" energy to provide carbon-free power to cities.