The biggest terrestrial tipping point or a potential carbon sink? 124 experts weigh in on the permafrost carbon feedback
Ben W. Abbott1 ([email protected]), 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
