An observation-based constraint on permafrost loss as a function of global warming

Abstract

Permafrost, which covers 15 million km 2 of the land surface, is one of the components of the Earth system that is most sensitive to warming 1,2 . Loss of permafrost would radically change high-latitude hydrology and biogeochemical cycling, and could therefore provide very significant feedbacks on climate change [3][4][5][6][7][8] . The latest climate models all predict warming of high-latitude soils and thus thawing of permafrost under future climate change, but with widely varying magnitudes of permafrost thaw 9,10 . Here we show that in each of the models, their present-day spatial distribution of permafrost and air temperature can be used to infer the sensitivity of permafrost to future global warming. Using the same approach for the observed permafrost distribution and air temperature, we estimate a sensitivity of permafrost area loss to global mean warming at stabilization of 4.0 +1.0 −1.1 million km 2 • C −1 (1σ confidence), which is around 20% higher than previous studies 9 . Our method facilitates an assessment for COP21 climate change targets 11 : if the climate is stabilized at 2 • C above pre-industrial levels, we estimate that the permafrost area would eventually be reduced by over 40%. Stabilizing at 1.5 • C rather than 2 • C would save approximately 2 million km 2 of permafrost.Permafrost, defined as ground that remains at or below 0 • C for two or more consecutive years, underlies 24% of the land in the Northern Hemisphere 12 . Under recent climate warming, permafrost has begun to thaw, causing changes in ecosystems and impacting northern communities, for example through collapse of roads and buildings as the ground becomes unstable 13 . Large quantities of carbon are stored in organic matter in permafrost soils 14 , which starts to decompose when the permafrost thaws, resulting in the emission of greenhouse gases such as carbon dioxide and methane. In the future, carbon release from permafrost thaw may have a significant impact on the Earth's climate 6 . Due to its global importance, numerous modelling studies have assessed the rate of permafrost thaw under future climate warming 9,10,15,16 . However, despite progress in process-based modelling on local and regional scales, for example, ref. 17, a lack of data availability and model limitations mean that permafrost is still poorly simulated in global climate models, where the historical simulations show a present-day permafrost area anywhere between 0.1 and 1.8 times the size of that observed 9 . Models often have shallow soil columns, a limited representation of soil properties, inadequate snow thermal and physical dynamics and other missing processes 9 . Here we present a projection of large-scale permafrost thaw that is based on observations, avoiding model bias, and accounting for observational uncertainty.Our approach is based on using the relationship between mean annual air temperature (MAAT) and permafrost occurrence

Statistical Forecasting of Current and Future Circum‐Arctic Ground Temperatures and Active Layer Thickness

“…Ground thermal regime is strongly coupled with average atmospheric conditions and is often characterized by using average annual air temperature or cumulative temperature sums (e.g., freeze and thaw days; Chadburn et al, 2017;Gruber, 2012;Smith, 1975). In addition, precipitation conditions affect ground surface temperatures through water infiltration to soil column causing advective heat transfer and modifying thermal properties of the soil (heat capacity and thermal conductivity; Weismüller et al, 2011;Westermann et al, 2011).…”

Permafrost Boundary Shift in Western Siberia May Not Modify Dissolved Nutrient Concentrations in Rivers

“…Due to the high importance of the Arctic Ocean and permafrost-dominated sub-arctic continental zones in the global carbon cycle and the high vulnerability of circumpolar zones to climate warming [20][21][22], numerous studies have been devoted to the biogeochemistry of organic carbon and nutrients in large rivers of the circumpolar zone [3,[23][24][25][26][27][28][29][30]. The main source of information on long-term fluxes of dissolved and suspended material from Northern Eurasia to the Arctic Ocean is data from the Russian Hydrometeorological Survey (RHS) collected at key gauging stations of almost all major Russian Arctic rivers [31][32][33][34].…”

Catastrophic Climate Change and Forest Tipping Points: Blind Spots in International Politics and Policy

“…Chadburn et al (2017) suggested that permafrost is more sensitive to global warming than previously believed: their study estimated that climate stabilization at 2°C greater than pre-industrial levels would eventually translate into a permafrost reduction of more than 40 per cent. However, it is the thawing of the permafrost (another tipping point of the Earth's climate system) that underlies large areas of the boreal that might have the most severe impact on the forests' resilience by changing the continental hydrological system, this phenomenon could permanently alter the local weather patterns to which boreal forests have adapted, potentially triggering the release of enormous amounts of GHGs.…”