An Assessment of the Carbon
Balance of Arctic Tundra:
Comparisons among
Observations, Models, and
Atmospheric inversions
A. David McGuire and Co-authors
U. Alaska Fairbanks and U.S. Geological Survey
AGU Fall 2011 Meeting, GC41F-01
8 December 2011
Lead Authors:
A.D. McGuire – University of Alaska Fairbanks, USA
T. R. Christensen – Lund University, Sweden
Co-authors:
Dan Hayes – Oak Ridge National Laboratory, USA
Arnaud Heroult – Lund University, Sweden
Eugenie Euskirchen – University of Alaska Fairbanks, USA
John Kimball – University of Montana, USA
Charles Koven – Lawrence Berkeley National Lab, USA
Peter Lafleur – Trent University, Canada
Paul Miller – Lund University, Sweden
Walt Oechel – San Diego State University, USA
Philippe Peylin – LSCE, France
Mathew Williams – University of Edinburgh, UK
Is the CO2 sink of N. High Latitudes Changing?
0.5
0.0
SOURCE
BONA
Cumulative NEE since 1960 (Pg C)
-0.5
-1.0
-1.5
(1)
BOEU
SINK
-2.0
-2.5
-3.0
BOAS
-3.5
-4.0
-4.5
-5.0
(2)
-5.5
-6.0
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Year
From Hayes et al. (2011, Global Biogeochemical Cycles)
Simulated Arctic Basin Terrestrial C Budget
Mean annual C fluxes and change in stocks (Tg C yr-1) for the
terrestrial component of the Arctic Basin, 1997 - 2006
From McGuire et al. (2010, Tellus)
Arctic Tundra Domain
as defined by the Regional Carbon Cycle Assessment
and Processes (RECCAP) Synthesis Activity
Results Organization
• Estimates based on flux observations
• Process model estimates
• Atmospheric inversion analyses
• Comparison of the estimates
• Conclusions
Analysis of Observations
• Includes both chamber-based and tower-based studies
• 250 estimates of CO2 and CH4 exchange
Synthesis of Tundra Observations
Annual exchange of CO2 cannot be distinguished from neutral balance
across the range of studies that have been conducted
Process-based Modeling
• Regional Applications of Models:
- TEM6 – Permafrost, Vertical SOM, CH4, Fire
- LPJ-Guess WHyMe – Permafrost, CH4, Fire
- Orchidee – with Cryoturbation
- Terrestrial Carbon Flux (TCF) – Diagnostic Model
• Global Applications of Trendy DGVMs: CLM4C, CLM4CN,
Hyland, LPJ, LPJ-Guess, Orchidee N, SDGVM,
Triffid
• Compared two decades: 1990 – 1999 and 2000 - 2006
• Spatial domain defined by RECCAP Arctic Tundra
mask
Mean NEE of Arctic Tundra Simulated by Process Models
Model
g C m-2 yr-1
(negative = sink)
Regional Apps.
1990-1999
2000-2006
LPJ-G WHyMe
-21
-24
Orchidee
TEM6
-28
-6
-34
-3
-
Global Apps.
CLM4C
CLM4CN
Hyland
LPJ
0
-1
0
-20
-1
-1
0
-3
LPJ-Guess
Orchidee N
-21
-1
-24
-3
SDGVM
-18
-16
TRIFFID
-8
-17
• NEE ranged between 0 and 34 g C m-2 yr-1 sink; sink increases between decades
Mean Seasonal Cycle of Carbon Fluxes
• All of the models indicate that July is the month of maximum NPP and NEP.
Interannual Anomalies of Carbon Fluxes
• Three of the four models
have a similar range of
interannual variability in
GPP, NPP, RH, and NEP.
• Correlations among the
models indicate that GPP,
NPP, and RH are generally
well correlated among the
models, but the interannual
variability in NEP is poorly
correlated among the
models.
Atmospheric Inversion Modeling
• 10 models
• 1985 – 2009 depending on model
• Spatial domain defined by RECCAP Arctic Tundra
mask
Mean NEE of Arctic Tundra Estimated by Inversion Models
Model
gC m-2 yr-1
(negative = sink)
1990-1999
2000-2006
C13_CCAM_law
-
26
C13_MATCH_rayner
-
-31
JENA_s96_v3.3
-
-13
JMA_2010
-35
-37
LSCE_an_v2.1
-
-14
LSCE_var_v1.0
15
22
NICAM_niwa_woaia
-19
-9
rigc_Patra
-
-48
• NEE ranged between 26 g C m-2 yr-1 source and 48 g C m-2 yr-1 sink
• Sink increases between decades
Mean Seasonal Cycle of Carbon Fluxes of Inversions
All of the models indicate that July is the month of maximum NEE.
Interannual Variability of Carbon Fluxes from Inversions
• Interannual anomalies vary from 2.1 to 13.1 g C m-2 yr-1 (standard deviation)
• Correlation of interannual anomalies is poor (mean r=0.03, range: -0.38 to 0.99)
Comparison of Regional NEE among Methods (Tg C yr-1)
Time Period
Regional
ProcessBased
Observations Models
Global
ProcessBased
Models
Inversion
Models
1990 - 1999
Central Estimate
77
-166
-78
-13
1990 -1999
Uncertainty
-436 to 275
-255 to -55
-188 to 0
-321 to 140
2000 - 2006
Central Estimate
-217
-187
-93
-117
2000 – 2006
Uncertainty
-621 to -21
-312 to -28
-222 to -1
-439 to 243
•
•
•
•
Observations and Inversions – Can’t be distinguished from neutral balance
Process-Model Simulations – Arctic tundra has been a sink in the 1990s and 2000s
Only one central estimate is a source (observations in 1990s – North America)
All methods indicate that Arctic tundra has become a stronger sink in the 2000s
Changes in the Seasonal Cycle of NEP
Estimated by the Regional Process Models
• LPJ-Guess WHyMe and Orchidee estimate greater uptake in early and mid-growing
season, while TEM6 estimates greater uptake in the late growing season
Arctic Tundra C Assessment Conclusions
• Estimates of NEE based on observations and inversions
have large uncertainties that cannot be distinguished
from neutral balance.
• Process models indicate that Arctic tundra acted as a
sink for CO2 in recent decades.
• Central estimates based on observations, processmodels, and inversions each suggest stronger sinks in
the 2000s than in the 1990s.
• Analyses of regional models identified that two of the
models had increased CO2 uptake in early and midgrowing season between decades, while a third model
had greater uptake in the late growing season.
• Simulation of the difference between production and
decomposition is important to improve for assessing
responses of Arctic tundra to projected climate change