How Much of the Earth's Surface is Underlain by Permafrost?

More than 80% of studies reporting the area on Earth underlain by permafrost refer to the extent of the permafrost region , which accounts for around 21 million km 2 (22% of the Northern Hemisphere's exposed land surface). Since each permafrost zone (continuous, discontinuous, sporadic, and isolated, which combined represent the permafrost region) is not entirely underlain by permafrost, the actual area underlain by permafrost ( permafrost area ) accounts for approximately 14 million km 2 (15% of the exposed land surface area in the Northern Hemisphere). Such overstatements create a general impression that there is 6 million km 2 more permafrost than currently estimated. I highlight the known differences between the terms permafrost region and permafrost area, along with explaining the possible reasons leading to these overstatements. Recent studies estimating permafrost area extent are summarized to provide a baseline for the geoscientific community and general public about the actual area underlain by permafrost for different parts of the globe.