The biggest terrestrial tipping point or a potential carbon sink? 124 experts weigh in on the permafrost carbon feedback

Ben W. Abbott1 (benabbo@gmail.com), EAG Schuur2, JB Jones3, FS Chapin iii3, and the Permafrost Carbon Network4  

The permafrost carbon feedback may be the largest terrestrial feedback to

climate change as well as one of the most likely to occur; however, it is not included

in current emissions negotiations and estimates of its strength vary by a factor of

thirty (15–500 Pg C by 2100).

We collected expert assessments from 124 permafrost-region scientists of the

response of high-latitude carbon balance to four warming scenarios.

Experts provided quantitative estimates of CO2 and CH4 release, change in

biomass, wildfire CO2 emissions, and hydrologic carbon flux by 2040, 2100,

and 2300.

•  Permafrost degradation•  Longer decomposition season•  Hydrologic release•  Wildfire

•  Nutrient release•  CO2 fertilization•  Longer growing season

111  Pg  C  

1800  Pg  C  

Based  on  carbon  inventories  from  Pan  et  al.  2011  

Paleocene-Eocene Thermal Maximum (55 million years ago)•  Global temperature increased 5°C, thawing all

permafrost and triggering carbon release•  170,000 years of unstable climateEarly Holocene (5-9 thousand years ago)•  Global temperature increased 1-2°C•  Some degradation but limited carbon release

followed by permafrost re-accumulationDeconto et al. 2012; Schirrmeister et al. 2002

2040 2100 2300

RCP 2.6

RCP 8.5

0

100

200

300

400

0

100

200

300

400

2040 2100 2300

Cum

ulat

ive

Pg C

Soil C releaseBiomass C uptake

Scientific understanding

of system

The System

Public and political perception of the

system

Expert assessment

Quantitative

Qualitative

−20

0

20

40

60

−50

0

50

100

150

200

2040 2100 2300

Tota

l cha

nge

in b

iom

ass

(Pg

C)

Perm

afro

st C

rele

ase

offs

et

by b

iom

ass

(%)

RCP 2.6

RCP 4.5

RCP 6.0

RCP 8.5

0

200

400

600

−60

−30

0

30

60

90

0

300

600

900

1200

1500

−60

−30

0

30

60

90

CO2 CH4

Boreal Tundra

Boreal Tundra

DOC POC Coast

Boreal Tundra

Boreal Tundra

DOC POC Coast

Boreal Tundra

Boreal Tundra

DOC POC Coast

Carb

on re

leas

e (P

g C

)Ch

ange

in B

iom

ass

Chan

ge in

fire

em

issi

ons

Chan

ge in

hyd

rolo

gic

flux

RCP 2.6

RCP 4.5

RCP 6.0

RCP 8.5

2040 2100 2300

CO2 CH4 CO2 CH4

2040 2100 2300

(Pg

C)

(Tg

C y

r−1 )

(Tg

C y

r−1 )

0  

500  

1000  

1500  

2000  

Organ

ic  carbo

n  (Pg)  

Can increased biomass offset carbon release from soils, streams, and wildfire across the

permafrost zone?

Most of the permafrost carbon feedback can still be avoided

•  For current emissions trajectory (RCP 8.5) there is a net permafrost release of 65-230 Pg C by 2100

•  Including warming from CH4 this represents 28-80% of GHG necessary to exceed United Nations 2°C target

•  However, RCP 2.6 results in five-fold less permafrost GHG release, suggesting 60-80% of permafrost feedback is preventable

•  Warming fundamentally alters fire and hydrologic carbon regimes

•  Disturbance such as drought, fire, and thermokarst are key uncertainties in predicting net carbon balance

•  Paleo evidence for permafrost tipping point between 2 and 5°C warming

Expert assessment

Tundra:  +8  (Living  biomass)  +9  (Deadwood  and  liCer)  =  17  Pg    

Boreal:  +15  (Living  biomass)  -­‐21  (Deadwood  and  liCer)  =  -­‐6  Pg    

Complete  biome  shi;  results  in    biomass  gain  of  only  11  Pg    

Tundra Boreal forest

Temperate forest

Massive losses, modest gains

Net ecosystem carbon balance(business as usual)

(active emissions reductions)

This work was supported by the National Science Foundation ARCSS program, Vulnerability of Permafrost Carbon Research Coordination Network, and the Observatoire des Sciences de l’Univers de Rennes

(OSUR), ECOBIO-CNRS.

Permafrost has thawed before

Permafrost carbon pool

Peatlands  

Shallow  soils  (<3m)  

Deep  soils  (>3m)  

References: •  Abbott et al. (submitted) Can increased biomass offset carbon release from permafrost region soils, streams, and wildfire? An

expert assessment. PNAS •  Schuur, et al. (2013) Expert assessment of vulnerability of permafrost carbon to climate change. Climatic Change•  Schuur and Abbott (2011) Climate change: High risk of permafrost thaw. Nature•  Pan, et al. (2011) A Large and Persistent Carbon Sink in the World's Forests. Science. •  Tarnocai, et al. (2009) Soil organic carbon pools in the northern circumpolar permafrost region, Glob. Biogeochem. Cycles •  DeConto, et al. (2012) Past extreme warming events linked to massive carbon release from thawing permafrost. Nature•  Schirrmeister, et al. (2002) Paleoenvironmental and paleoclimatic records from permafrost deposits in the Arctic region of Northern

Siberia. Quatern Int

Sample of expertsCarbon Biomass Wildfire Water

Number of respondents 41 46 34 35Primary study region

Asia 11 10 3 8Europe 9 12 5 9

North America 26 27 27 18Circumpolar 15 12 6 9

Primary study biome      Arctic 26 31 13 27

Boreal 29 27 29 18Combined years of experience 750 762 533 521

Ratio male:female 3.7 2.6 2.8 4.9

Sources of uncertaintyBiomass Wildfire Hydrologic flux

Source of uncertainty % Source of uncertainty % Source of uncertainty % Water balance 56 Vegetation shift 73 Water balance 41

Wildfire 47 Water balance 58 Hydrologic flowpath 39 Permafrost degradation 40 Human disturbance 27 Permafrost degradation 24

Human disturbance 29 Permafrost degradation 18 Photo and bio-lability 24 Insect damage 27 Seasonality 15 Vegetation shift 20 Vegetation shift 24 Regional differences 12 Fluvial erosion 11

Treeline dynamics 16      Nutrient availability 13      

Non-insect herbivores 11      

P-1116-01

1Observatoire des Sciences de l’Univers de Rennes2Northern Arizona University, Center of Ecosystem Science and Society3Institute of Arctic Biology/Department of Biology & Wildlife, University of Alaska Fairbanks 4www.permafrostcarbon.org

Tarnocai et al. 2009

Carbon source … or carbon sink