How much of the Northern Hemisphere’s land surface is underlain by permafrost?

Permafrost, which is defined as ground that remains at or below 0 °C (32 °F) for two or more years, is estimated to underlie approximately 24 percent of the land surface in the Northern Hemisphere.1

This perennially frozen ground is widespread throughout the Arctic and subarctic regions. Its distribution is generally categorized into two zones:1
* Continuous zone: Found in the far north, where permafrost is present nearly everywhere except beneath unfrozen bodies of water.2
* Discontinuous zone: Located further south, where permafrost-free areas become increasingly common.2

In addition to these northern regions, permafrost also exists at lower latitudes in high-elevation areas, where it is known as alpine permafrost.2