As I understand it, for much of the permafrost, there's ongoing vegetation growth, and has been for millennia, with a carbon cycle that's sequesters more carbon

As I understand it, for much of the permafrost, there's ongoing vegetation growth, and has been for millennia, with a carbon cycle that's sequesters more carbon than most other places. The plants grow slowly, extracting CO2, die, but don't rot due to conditions, so the levels stored in the soils keep on increasing, and the land rising. Not dissimilar to peat bogs in temperate regions, though the detail is different. A thaw would release the thousands of years of stored carbon, and could promote growth that sequesters less carbon.