Why does permafrost become thinner toward its southern boundary?

Permafrost becomes thinner toward its southern boundary primarily due to the thermal balance between the heat flow from Earth’s interior and the heat lost to the atmosphere.1

As the mean annual air temperature increases toward the south, the amount of heat reaching the ground surface rises, which directly influences the temperature of the permafrost. Because the thickness of permafrost is controlled by this thermal equilibrium, higher surface temperatures result in a shallower base of permafrost. Near the southern limit, the temperature of the permafrost is typically near 0 °C (32 °F), and the layer becomes increasingly thin and discontinuous until it eventually disappears.12

Additionally, local factors such as solar radiation, vegetation, and snow cover play critical roles in this thinning process. Vegetation acts as an insulating layer, and its disturbance can lead to localized thawing, while snow cover can prevent heat from escaping the ground during winter, causing the permafrost to become warmer and thinner.3