The timing of Late Pleistocene-early Holocene permafrost degradation across the Northern Hemisphere (2023)

Arctic warming is causing widespread thawing of perennially frozen ground (permafrost). Once thawed, the ancient carbon contained in permafrost decomposes, releasing greenhouse gasses. Carbon dioxide and methane from thawing high-latitude permafrost could trigger a permafrost carbon feedback (P-CF), a potentially critical tipping element in Earth’s climate system. The sensitivity of this feedback to past warming events, however, has not been fully assessed. To address this, we review and analyze a compilation of already-published permafrost thaw indicators, soil-carbon maps, and paleoclimate time series to evaluate the instability of the global permafrost domain in the context of major global warming and greenhouse gas increases which occurred during the last global deglaciation (21.0-8.0 thousand years before 1950, or ka). We find it extremely unlikely that permafrost carbon contributed significantly to net increases of atmospheric greenhouse gasses at any point during the last deglaciation. Instead, most greenhouses gasses came from the ocean, low latitude soils, and tropical wetlands. A large amount of permafrost carbon was vulnerable to release during the early Holocene (11.7-8.0 ka), but was largely offset by negative feedbacks such as enhanced carbon storage in the peatlands and boreal forests that expanded in regions formerly occupied by ice sheets. The paleo-perspectives described here suggest that only under the most extreme future emissions scenarios will a strong permafrost-carbon feedback occur. Empty fields indicate variables not reported by the original authors; values of N/A indicate fields which are not relevant for a particular thaw observation (i.e 14C age for a U/Th-derived speleothem drip age).