Chapter 11, Key Finding 2

Soils in the northern circumpolar permafrost zone store 1,460 to 1,600 petagrams of organic carbon (Pg C), almost twice the amount contained in the atmosphere and about an order of magnitude more carbon than contained in plant biomass (55 Pg C), woody debris (16 Pg C), and litter (29 Pg C) in the boreal and tundra biomes combined. This large permafrost zone soil carbon pool has accumulated over hundreds to thousands of years. There are additional reservoirs in subsea permafrost and regions of deep sediments that are not added to this estimate because of data scarcity (very high confidence).