An Assessment of the Carbon Balance of Arctic Tundra in North

America:Comparisons among

Observations, Models, and Atmospheric inversions

A. David McGuire and Co-authorsU. Alaska Fairbanks and U.S. Geological Survey

NACP All-Investigators MeetingFebruary 4, 2013

Co-authors:T.R. Christensen – Lund University, SwedenDan Hayes – Oak Ridge National Laboratory, USAArnaud Heroult – Lund University, SwedenEugenie Euskirchen – University of Alaska Fairbanks, USAJohn Kimball – University of Montana, USACharles Koven – Lawrence Berkeley National Lab, USAPeter Lafleur – Trent University, CanadaPaul Miller – Lund University, SwedenWalt Oechel – San Diego State University, USAPhilippe Peylin – LSCE, FranceMathew Williams – University of Edinburgh, UKYonghong Yi – University of Montana, USA

From Hayes et al. (2011, Global Biogeochemical Cycles)From Hayes et al. (2011, Global Biogeochemical Cycles)

-6.0

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

Cu

mu

lati

ve N

EE

sin

ce 1

960 (

Pg

C) BONA

BOAS

BOEU

(1)

(2)

-6.0

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

Cu

mu

lati

ve N

EE

sin

ce 1

960 (

Pg

C) BONA

BOAS

BOEU

(1)

(2)

Is the CO2 sink of N. High Latitudes Changing?

Is the CO2 sink of N. High Latitudes Changing?

SOURCE

SINK

Arctic Tundra Domainas defined by the Regional Carbon Cycle Assessment

and Processes (RECCAP) Synthesis Activity

McGuire et al. 2012. An assessment of the carbon balance of arctic tundra: Comparisons among observations, process models, and atmospheric inversions. Biogeosciences 9: 3185-3204, doi:10.5194/bg-9-3185-2012.

Analysis of Observations (1990 – 2009)

• Includes both chamber-based and tower-based studies

• ~225 estimates of CO2 exchange tundra-wide

• ~110 North America CO2 exchange estimates for tundra

• ~152 estimates of CH4 exchange tundra-wide

• ~45 North America CH4 exchange estimates for tundra

Synthesis of Tundra Observations

Annual exchange of CO2 cannot be distinguished from neutral balance across the range of studies that have been conducted

Summary of Observationally Based Estimates of Mean Net CO2-C and CH4-C Exchange from Arctic Tundra to the Atmosphere (g C

m-2 season-1) for Different Subregions 

Time Period North America North Atlantic Northern Europe Eurasia 

CO2 Exchange 

Summer

Before 2000 -7 (521; -22 to 72) -32 (9; -58 to -5) -98 (4; -127 to -68) -25 (18; -50 to -1)

Since 2000 -18 (28; -39 to 3) -53 (12; -90 to 16) -92 (5; -220 to 36) -73 (12; -141 to -4) 

Annual

Before 2000 29 (9; 2 to 57) - -25 (6; -63 to -14) -

Since 2000 -3 (14; -28 to 21) - -19 (33; -30 to -8) -

CH4 Exchange 

Summer

Before 2000 2.4 (10; 0.7 to 4.2) - 7.8 (13; 1.4 to 14.2) 3.0 (15; -0.4 to 6.5)

Since 2000 1.4 (9; -0.2 to 2.9) - 12.5 (10; 1.9 to 23.0) 5.1 (29; 1.6 to 8.6)

Annual

Before 2000 4.4 (24; 1.4 to 7.4) - 15.0 (3; -18.3 to 48.3) -

Since 2000 16.9 (2; -12.0 to 45.7) - 11.3 (27; 6.6 to 16.0) 8.2 (7; -1.8 to 18.1)

 1Number of site-year estimates295% confidence interval

Summary of Observationally Based Estimates of Mean Net CO2-C and CH4-C Exchange from Arctic Tundra to the Atmosphere (g C

m-2 season-1) for Different Tundra Types

 

Time Period Wet Tundra Dry/Mesic Tundra 

CO2 Exchange 

Summer -43 (451; -27 to -592) 5 (46; -11 to 21)

Winter 31 (3; 1 to 61) 31 (7; 11 to 51)

 Annual -26 (27; -15 to -37) 10 (12; -27 to 47)

  

CH4 Exchange 

Summer 9.2 (38; 5.4 to 13.0) 0.8 (25; 0.3 to 1.4)

 Annual 14.6 (22; 8.5 to 20.2) 2.3 (24; 0.3 to 4.3)

  1Number of site-year estimates295% confidence interval

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

Model 1990-1999 2000-2006g C m-2 yr-1

(negative = sink)Regional Apps.

LPJ-G WHyMe -21 (-241) -24 (-251)

Orchidee -28 -34TEM6 -6 (-11) -3 (31)

-Global Apps.

CLM4C 0 -1CLM4CN -1 -1Hyland 0 0

LPJ -20 -3

LPJ-Guess -21 -24Orchidee N -1 -3

SDGVM -18 -16

TRIFFID -8 -17

Mean NEE of Arctic Tundra Simulated by Process Models

• NEE ranged between 0 and 34 g C m-2 yr-1 sink; sink increases between decades1 Results for North America

Changes in the Seasonal Cycle of NEPEstimated by the Regional Process Models

• In the 2000s, LPJ-Guess WHyMe and Orchidee estimate greater uptake in early and mid-growing season, while TEM6 estimates greater uptake in the late growing season; lower NEP in October driven by greater RH during the 2000s in all 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

• NEE ranged between 26 g C m-2 yr-1 source and 48 g C m-2 yr-1 sink• Sink increases between decades

Model 1990-1999 2000-2006gC m-2 yr-1

(negative = sink)

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

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)

• 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

Time Period Observations

Regional Process-

Based Models

Global Process-

Based Models

Inversion Models

1990 - 1999Central Estimate

N. AMERICA138126

-166-53

-78- -13

-1990 -1999Uncertainty

N. AMERICA-102 to 378

8 to 243-255 to -55-102 to -4

-188 to 0-

-321 to 140-

2000 - 2006Central Estimate

N. AMERICA-202-14

-187-47

-93- -117

-2000 – 2006Uncertainty

N. AMERICA-628 to 224-118 to 90

-312 to -28-107 to 13

-222 to -1-

-439 to 243-

Comparison of Regional CH4 among Methods (Tg C yr-1)

• Process-Model Simulations – tundra emissions are higher than observed estimates,but not for North America.

• Substantial overlap in uncertainties between observations and model estimates.• Both methods suggest that methane emissions increased from 1990s to 2000s.

Time Period Observations

Regional Process-

Based Models

Global Process-

Based Models

Inversion Models

1990 - 1999Central Estimate

N. AMERICA103

252

--

--

1990 -1999Uncertainty

N. AMERICA-1 to 221 to 6

15 to 341 to 3

--

- -

2000 - 2006Central Estimate

N. AMERICA2013

282

--

--

2000 – 2006Uncertainty

N. AMERICA-11 to 51-10 to 35

18 to 371 to 3 - -

Arctic Tundra C Assessment Conclusions• Estimates of NEE based on observations and inversions have large uncertainties that cannot be distinguished from neutral balance, except for observations of tundra in North America in 1990s.

• Process models generally indicate that Arctic tundra acted as a sink

for CO2 in recent decades.

• Central estimates based on observations, process-models, and inversions each suggest stronger sinks for CO2 (except central estimates of process-models for North America) and stronger sources of CH4 in the 2000s vs. 1990s.

• There is a need to reduce uncertainties from observations by better stratification of observations between wet and dry/mesic tundra.

• Simulation of the difference between production and decomposition

is important to improve in models for assessing responses of Arctic tundra to projected climate change.