Permafrost carbon-climate feedbacks accelerate global warming

Abstract

International audiencePermafrost soils contain enormous amounts of organic carbon, which could act as a positive feedback to global climate change due to enhanced respiration rates with warming. We have used a terrestrial ecosystem model that includes permafrost carbon dynamics, inhibition of respiration in frozen soil layers, vertical mixing of soil carbon from surface to permafrost layers, and CH4 emissions from flooded areas, and which better matches new circumpolar inventories of soil carbon stocks, to explore the potential for carbon-climate feedbacks at high latitudes. Contrary to model results for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4), when permafrost processes are included, terrestrial ecosystems north of 60°N could shift from being a sink to a source of CO2 by the end of the 21st century when forced by a Special Report on Emissions Scenarios (SRES) A2 climate change scenario. Between 1860 and 2100, the model response to combined CO2 fertilization and climate change changes from a sink of 68 Pg to a 27 + -7 Pg sink to 4 + -18 Pg source, depending on the processes and parameter values used. The integrated change in carbon due to climate change shifts from near zero, which is within the range of previous model estimates, to a climate-induced loss of carbon by ecosystems in the range of 25 + -3 to 85 + -16 Pg C, depending on processes included in the model, with a best estimate of a 62 + -7 Pg C loss. Methane emissions from high-latitude regions are calculated to increase from 34 Tg CH4/y to 41-70 Tg CH4/y, with increases due to CO2 fertilization, permafrost thaw, and warming-induced increased CH4 flux densities partially offset by a reduction in wetland extent

Modeling permafrost thaw and ecosystem carbon cycle under annual and seasonal warming at an Arctic tundra site in Alaska

“…Permafrost thaw subject to climate warming can liberate formerly frozen C, which is then released to atmosphere [Davidson et al, 2006;Schuur et al, 2008Schuur et al, , 2009Tarnocai et al, 2009;Grosse et al, 2011;Koven et al, 2011;van Huissteden et al, 2011;Harden et al, 2012;Knoblauch et al, 2013;Pries et al, 2013;Schuur et al, 2013]. This suggests that enhanced permafrost thawing from warming potentially leads to more C loss and may shift the ecosystem C balance toward a weaker sink or a source [Osterkamp and Jorgenson, 2006;Osterkamp, 2007;Schuur et al, 2008].…”

“…It was recently hypothesized that the permafrost thawed carbon can be up to 147-436 pg C from 2050 to 2100 [Harden et al, 2012;Schuur et al, 2013]. Other Earth System models simulated a 62 pg C loss as permafrost C feedback to climate warming [Koven et al, 2011]. The additional warming is about 0.04-0.23°C at the end of this century [Schneider von Deimling et al, 2012] and 0.2-1.7°C warming in two centuries [MacDougall et al, 2012].…”

Modelling Tundra Vegetation Response to Recent Arctic Warming

“…A number of climate model-based studies have concluded that the decline in albedo resulting from the masking of snow by protruding trees and tall shrubs could amplify warming in affected areas to a degree comparable seasonally with the direct anthropogenic forcing of climate (Betts 2000;Claussen et al 2001;Göttel et al 2008;Wramneby et al 2010;Matthes et al 2012Bonfils et al 2012. Additional feedback mechanisms involving the effects of ecosystem changes on evapotranspiration and carbon balance are in general predicted to further amplify warming (Swann et al 2010;Koven et al 2011, Bonfils et al 2012. Chapin et al (2005) have estimated that albedo changes resulting from shrub expansion in arctic Alaska increased atmospheric heating locally by some 3 W m -2 locally over the 1980s and 1990s.…”

Soil geochemistry confines microbial abundances across an arctic landscape; implications for net carbon exchange with the atmosphere

“…This is of concern because a large proportion of the World's terrestrial organic carbon is stored in permafrost soils. There is growing evidence that thawed ''old'' carbon is being rapidly mobilised to carbon dioxide (CO 2(g) ) and methane (CH 4(g) ), increasing net gas releases to the atmosphere (Schuur et al 2009;Koven et al 2011;Allen et al 2014). For example, an estimated 190 ± 64 Gt C of additional permafrost carbon could be released by 2200 (Schaefer et al 2011) and a 31 % increase in Arctic CH 4(g) emissions was already observed between 2003 and 2007 (Bloom et al 2010).…”