Regional trends in the land carbon
cycle and the underlying mechanisms
over the period, 1980-2009
S. Sitch, P. Friedlingstein, G. Bonan, P. Canadell, P. Ciais, P.M. Cox, P.
Foster, E. Gloor, K. Goldewijk, C. Huntingford, G. Hurtt, C. D. Jones, S.
Piao, I.C. Prentice, C. Le Quere, P. Levy, M. R. Lomas, L. Mercado, B.
Mueller, M. Reichstein, S. Running, S. I. Seneviratne, E. Shevliakova, P.
Thornton, N. Viovy , G. van der Werf, F. I. Woodward, S. Zaehle, M.
Zhao
Terminology
Net ecosystem exchange NEE
RH -
Photosynthesis
CO2
Net Primary productivity (NPP)=
Gross Primary productivity (GPP)=
Photosynthesis +leaf respiration
GPP-Plant respiration
Plant respiration
CO2
CO2
Soil respiration
(heterotrophic)
RH
NPP
Key Diagnostic of the Carbon Cycle
CO2 Partitioning (PgC y-1)
Evolution of the fraction of total emissions that remain in the atmosphere
10
Total
CO2 emissions
8
6
Atmosphere
4
2
1960
1970
1980
1990
Data: NOAA, CDIAC; Le Quéré et al. 2009, Nature-geoscience
2000
2010
Fate of Anthropogenic CO2 Emissions (2000-2008)
1.4 PgC y-1
4.1 PgC y-1
45%
7.7 PgC y-1
+
3.0 PgC y-1
29%
26%
2.3 PgC y-1
Le Quéré et al. 2009, Nature-geoscience; Canadell et al. 2007, PNAS, updated
Modelled Natural CO2 Sinks
Le Quéré et al. 2009, Nature-geoscience
Regional Trends in C-sinks and Annual Global Budget
Global Annual Budget
 Regional Trends in Land C-Sinks (Trendy)
Compare DGVM-based estimates with other
evidence
- Satellite derived data
- Fluxtower data
- Atmospheric Monitoring Stations
Trendy Protocol
GCP- Land trends: modelling protocol
Contact: Stephen Sitch (s.sitch@leeds.ac.uk) & Pierre Friedlingstein
(pierre.friedlingstein@bristol.ac.uk)
Goal: To investigate the trends in NEE over the period 1980-2009
Participating models
JULES, LPX, ORCHIDEE, O-CN, HyLand, SDGVM, NCAR CLM4,
GFDL/Princeton
Model simulations
The models will be forced over the 1860-2009 period with changing
CO2, climate (CRU/NCEP) and land use:
S1: CO2 only
S2: CO2 and climate
S3 (optional): CO2, climate and land use
Trends in Land Processes
Land Sink trend
positive NPP trend > positive RESP trend
negative NPP trend > negative RESP trend
positive NPP trend, negative RESP trend
Land Source trend
positive NPP trend < positive RESP trend
negative NPP trend < negative RESP trend
negative NPP trend, positive RESP trend
Climatic Drivers of Trends in Land Processes
Land Sink trend
positive NPP trend > positive RESP trend
negative NPP trend > negative RESP trend
positive NPP trend, negative RESP trend
Land Source trend
positive NPP trend < positive RESP trend
negative NPP trend < negative RESP trend
negative NPP trend, positive RESP trend
Satellite Evidence: Trends in Soil Moisture
B. Mueller, ETH Zurich
Remarkable Similarity between NPP evolution from DGVMs
1.35
1.3
TRIF FNPP
Fractional NPP Change
1.25
1.2
1.15
LPJ FNPP
SDGVM FNPP
1.1
1.05
1
0.95
1900
1920
1940
1960
Year
1980
2000
Global NPP explains most of the NEE variability
4
3
2
1
0
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
-1
-2
NEE_4DGVMs_anomaly
-3
-4
NPP_4DGVMs_anomaly
DGVM sink vs MODIS-NPP)
M Zhao
Alternative Upscaling Approaches
Multidimensional flux patterns...
century
forest
inventory
plot
Forest/soil inventories
decade
Color: GPP
month
Landsurface remote sensing
Eddy
covariance
towers
week
H [MJ m-2 yr-1]
Temporal scale
year
tall
tower
observatories
2000
remote sensing
of CO2
day
0
hour
0
local 0.1
1
plot/site
10
100
1000
Spatial scale [km]
10 000 global
2000
LE [MJ m-2 yr-1]
Countries EU
... models to be cross-evaluated against.
Reichstein
Future Precipitation Changes (Summer Droughts?)
JJA
http://www.ipcc.ch/
Stippled areas > 90% of the models agree in the sign of the change
Summary
 Use set-up to produce global/regional annual C-budgets
 Drought may be an important driver of the present-day
trends in the land carbon cycle
 Climate Models Project Summer Drought in Continental
Regions
 Drought may be an important driver of the future trends
in the land carbon cycle
 Critical to understand Ecosystem Response to Drought
for future Earth System feedbacks