Subsea permafrost carbon stocks and climate change sensitivity estimated by expert assessment

Sayedeh Sara Sayedi,Jennifer M Frederick,Alexander Vasiliev,Christina Schädel,Sarah Baeumler,Matt O’Regan,Cuicui Mu,Paul Overduin,Gleb Kraev,Martin Jakobsson,Mehran Ghandehari,Shengping He,Jorien E Vonk ,K M Schreiner ,Brian Brown ,А В Гаврилов ,Edward A G Schuur ,Nikita Demidov,Annie Bourbonnais,A David Mcguire ,Elena Pizhankova,Dongjoo Joung,Tingjun Zhang,Miriam C Jones ,Benjamin W Abbott ,Sebastian Westermann,J P Zarnetske ,Gustaf Hugelius,Christian Stranne,Brett F Thornton ,R W Macdonald ,Rebecca J Frei

doi:10.1088/1748-9326/abcc29

Abstract

The continental shelves of the Arctic Ocean and surrounding seas contain large stocks of organic matter (OM) and methane (CH4), representing a potential ecosystem feedback to climate change not included in international climate agreements. We performed a structured expert assessment with 25 permafrost researchers to combine quantitative estimates of the stocks and sensitivity of organic carbon in the subsea permafrost domain (i.e. unglaciated portions of the continental shelves exposed during the last glacial period). Experts estimated that the subsea permafrost domain contains ∼560 gigatons carbon (GtC; 170–740, 90% confidence interval) in OM and 45 GtC (10–110) in CH4. Current fluxes of CH4 and carbon dioxide (CO2) to the water column were estimated at 18 (2–34) and 38 (13–110) megatons C yr−1, respectively. Under Representative Concentration Pathway (RCP) RCP8.5, the subsea permafrost domain could release 43 Gt CO2-equivalent (CO2e) by 2100 (14–110) and 190 Gt CO2e by 2300 (45–590), with ∼30% fewer emissions under RCP2.6. The range of uncertainty demonstrates a serious knowledge gap but provides initial estimates of the magnitude and timing of the subsea permafrost climate feedback.

Highlights

Effective mitigation of climate change requires knowledge of human climate forcing and the ecosystem feedbacks that could amplify or stabilize the response of the Earth system (Lenton et al 2008, 2019)
Past and present subsea permafrost degradation and carbon dynamics The median estimate by the group of experts for the area of formerly subaerial permafrost inundated after the Last Glacial Maximum (LGM) was 3.5 million km2 (2.5–4.4; range is the 90% confidence interval), which agrees closely with estimates from the literature (Lindgren et al 2016, Overduin et al 2019)
Experts estimated that 500 gigatons carbon (GtC) (250–750) in soil organic matter (SOM) was stored in and on the continental shelves at the LGM (figure 2(b))

Summary

Introduction

Effective mitigation of climate change requires knowledge of human climate forcing and the ecosystem feedbacks that could amplify or stabilize the response of the Earth system (Lenton et al 2008, 2019). Due to complexity and limited data, quantitative estimates of some ecosystem feedbacks are not available and will not be available in the foreseeable future (Schuur et al 2013, Abbott et al 2016, Steffen et al 2018) This creates potentially severe knowledge gaps, where known but unquantified ecosystem feedbacks may be disregarded during the selection of climate targets and regulatory policies (Barrett and Dannenberg 2012, Turetsky et al 2020). Recent research has improved understanding of the terrestrial climate feedback from permafrost (Schuur et al 2015, Mcguire et al 2018, Natali et al 2019, Turetsky et al 2020), but potential emissions from the subsea permafrost domain (figure 1) remain unknown because of limited observational data and modeling estimates (Schuur et al 2015, Shakhova et al 2017, Martens et al 2019). This ecosystem feedback is virtually absent from climate policy discussions (table S1 available online at https://stacks.iop.org/ERL/15/124075/mmedia)

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