The Coupled Climate-Carbon Cycle Model Intercomparison Project (C4MIP)
Protocol for Phase 1: atmosphere-land interactions
Introduction
Interactions between climate and the carbon cycle have the potential to provide major
feedbacks on climate change, but major uncertainties in the magnitude of these
feedbacks persists. The coupled climate-carbon cycle model intercomparison project
(C4MIP) aims to investigate the plausible sensitivity range of the climate-carbon
cycle system by using a number of independent models driven by a common set of
forcings.
The potential feedbacks may be mediated by altered forcing of the ocean and
terrestrial carbon cycles by climate change and also by the impact of consequent
changes in CO2 concentrations on radiative forcing of climate.
Hence, the ultimate aim of C4MIP is to perform a suite of simulations of 20th and
21st Century climate change including the atmospheric, terrestrial and oceanic
components of the climate-carbon cycle system. However, before embarking on an
intercomparison of such "full-form models" (of which 2 examples currently exist),
C4MIP will perform simulations with the atmospheric and terrestrial biosphere submodels coupled together but with ocean temperatures and carbon fluxes prescribed.
The simulations cover the 20th Century only, to allow the use of observational data
for forcing and validation. This study will provide key information on the
mechanisms and robustness of land-atmosphere interactions in the models, which will
aid with assessment and understanding of the full-form experiments. Not only will it
provide new insight into the behaviour of the 2 existing full-form models, it will allow
intercomparison with other models which will include the terrestrial component of the
carbon cycle before the oceanic component.
This initial coupled land-atmosphere carbon cycle experiment will complement other
model intercomparison studies which are examining other components of the Earth
system in parallel with C4MIP. The NOCES experiment will explore the behaviour
of the ocean carbon cycle subject to observed climate and CO2 forcing. The Coupled
Model Intercomparison Project (CMIP) will provide analyses of the climate
sensitivity of the physical climate models used in C4MIP. Finally the Climate of the
20th Century (C20C) experiment will explore the sensitivity of the land-atmosphere
physical models to observed forcing by SSTs and radiative forcing. Where possible
we hope to make our experiment compatible with these so that the sensitivity
information they yield is directly applicable to C4MIP. To that end we will use
forcings for the physical climate models taken from Noces and C20C (these are very
similar) and for the carbon cycle from Noces.
Model requirements
Participation in C4MIP Phase 1 requires a coupled global model system comprising
of:
1. An atmospheric General Circulation Model (GCM) able to transport tracers
2. A terrestrial carbon cycle model able to account for land use changes
The models should be as follows:
a. The terrestrial biosphere model should take input meteorological data from the
atmospheric GCM.
b. Land-atmosphere CO2 fluxes should be passed from the terrestrial biosphere
model to the atmosphere model.
c. The terrestrial biosphere model should update the physical land surface
boundary conditions in the atmosphere as a result of:
i)
the imposed land use changes
ii)
the responses of dynamic vegetation, if included in
the model
The coupling should be synchronous (ie: involving time-dependent exchange of
information) rather than involving long-term climatological means.
Overview of experiment
Main simulation
The primary objective is to examine the simulation of 20th Century atmospheric CO2
and the CO2 fluxes at the land surface in the coupled atmosphere-terrestrial biosphere
models. These quantities will be compared between the models and with observations
to examine the consistency of the various observed and simulated changes in the landatmosphere carbon cycle.
Each coupled atmosphere-terrestrial biosphere model will simulate the climate and
terrestrial carbon budget of the 20th Century, forced by historical
observations/reconstructions of atmospheric CO2, sea-surface temperatures (SSTs)
and anthropogenic land cover change. In the last few decades of the simulation, the
atmosphere submodels will additionally simulate the spatial and temporal structure of
atmospheric CO2. This component of the simulation will be forced by the landatmosphere fluxes simulated by the terrestrial biosphere submodels, along with fossil
fuel emissions and ocean-atmosphere fluxes prescribed externally. The simulated 3D
CO2 field is for diagnostic purposes only, and will not exert any further influences on
radiative forcing, plant physiology or surface CO2 fluxes. These processes will
continue to depend on the prescribed global-mean CO2 concentration, avoiding the
complication of feedbacks.
Secondary simulations
As well as the main simulation, further simulations may use subsets of the above
time-dependent forcings with other forcings left unchanged in time. Is it intended that
these decomposed simulations will inform a better understanding of synergisms
between the forcings.
The groups will also be encouraged to perform 4 further simulations parallel to the
final 20 years of the main simulation, with slight perturbations to the initial
conditions. The ensemble of 5 simulations will allow the importance of internal
variability to be assessed. Sets of perturbated starting conditions will be generated
from data archived from the main run, for example through the use of a number of
consecutive days of archived data.
These secondary simulations are optional for the individual groups, but are highly
encouraged.
Forcing variables
The time-dependent forcing variables for the main simulation are therefore:
i)
CO2:
global annual mean
ii)
SSTs:
monthly mean spatial fields
iii)
land use:
annual mean spatial fields
iv)
fossil fuel:
annual mean, spatial fields
v)
ocean fluxes:
monthly mean spatial fields
"Fossil fuel" emissions also include emissions from cement production.
The data sources for these forcings are listed in Annex 1.
Figure 1 illustrates the application of the forcings to the main simulation. SSTs are
applied to the physical atmosphere submodel alone, and land use is applied to the
terrestrial biosphere submodel alone. The prescribed global mean atmospheric CO2 is
applied to both submodels. In the later stages, fossil fuel and ocean fluxes are applied
to the atmospheric CO2 transport submodel alone.
Suggested sets of forcings for the decomposed simulations are:
a. Time-dependent CO2 and SSTs, but land use fixed at initial state
b. Time-dependent land use, but CO2 and SSTs fixed at initial state
c. Time-dependent SSTs, but CO2 and land use fixed at initial state
The final 20-year ensemble simulations will use the same forcings as the main
simulation, but with small perturbations to the initial conditions.
Sea-surface
temperatures
(2-D monthly
means)
Atmospheric General
Circulation Model
Atmospheric
CO2 (global
annual
means)
Surface
climate
Land surface
properties
Atmospheric CO2
(3-D monthly means)
Net
CO2
fluxes
Terrestrial biosphere model
Land use
(2-D annual
means)
Fossil fuel CO2
emissions (2-D
annual means)
Ocean-atmosphere
CO2 fluxes (2-D
seasonal means)
Figure 1. Application of forcings to transient simulations
Spinup procedure
The simulation will begin at 1900. To provide spin-up conditions with minimal bias
introduced by interannual and interdecadal variability, the spin-up will consist of two
stages:
1. Equilibrate the model to near pre-industrial conditions, defined as 1850 CO2
and repeated cycles of 1875-1899 SSTs
2. Force the model by 2 cycles of 1875-1899 SSTs, increasing CO2 from 1850 to
1899
Attainment of pre-industrial equilibrium may require several centuries of simulation
of the terrestrial biosphere, which will exceed the available computational resources if
performed synchronously coupled to the atmosphere. An accelerated spinup with
asynchronous coupling is therefore permitted. This may either involve an extended
internal timestep for the terrestrial biosphere submodel, or a 3-stage process of offline
spinup prior to coupling:
1a. Run the atmosphere submodel for 25 years with 1875-1899 SSTs and 1850 CO2.
Save all variables needed to run the terrestrial model
1b. Run the terrestrial biosphere model offline for 1,000 years, with climate variables
from step (1a) as input variables repeatedly cycled over the 25 years.
1c. Couple the 2 submodels and run for the 1875-1899 period under 1850 CO2,
initialising at the terrestrial state from the 1000-year offline integration.
In all stages during spin-up, land use will be fixed at the 1900 state.
Transient simulation, 1900-2000
The transient simulation will be forced by historical SSTs, global mean CO2 and land
use from 1900-2000. The atmosphere and terrestrial biosphere submodels will
interact through the surface meteorology, hydrology and radiation budget. Landatmosphere CO2 fluxes will be simulated by the terrestrial biosphere model, but these
will not be used to update the atmospheric CO2 concentration provided as a forcing.
The methodology for calculating carbon fluxes following land cover changes will be
taken from the Grand Slam CCMLP experiment (see Grand Slam protocol).
Simulation of atmospheric CO2 tracer transport as a passive diagnostic will begin at
1959, so fossil fuel emissions and ocean-atmosphere CO2 fluxes will be additional
forcings from that time. CO2 updated by fossil fuel emissions, the terrestrial
biosphere and ocean fluxes should be transported separately. The atmosphere and
terrestrial biosphere submodels will continue to be forced with observed global mean
CO2.
Ensemble simulations will begin at 1980, so starting conditions will be saved from the
main run at this time.
Diagnostics
The primary validation will consist of comparing the simulated 3-dimensional
diagnostic CO2 fields against observations at the stations listed in Annex 2. Other
atmospheric and biospheric variables are required for validation against historical
climate records and intercomparison with the other models.
3D monthly-mean fields:
Temperature
Specific humidity
Atmospheric CO2 concentration from each tracer (fossil, ocean and land)
2D monthly-mean fields:
Outgoing Longwave Radiation (OLR)
Presence/fractional cover of plant functional types (PFTs)
All terrestrial carbon pools and fluxes
- including products and conversion flux from land use
- carbon pools and fluxes should be saved per PFT if fractional covers are
accounted for
LAI (of PFTs if fractional covers are accouted for)
Daily mean 2D surface fields:
Surface temperature
precipitation,
upward surface shortwave radiation
downward surface shortwave radiation
upward surface longwave radiation
downward surface longwave radiation
wind stress
atmospheric pressure
soil temperature
soil water content
+ any other field needed to run the terrestrial carbon cycle offline
latent heat flux, sensible heat flux, LAI, GPP, NPP, NEP, gs
Hourly time series at selected gridpoints:
Atmospheric CO2 at station locations listed in Annex 2.
Data format
Forcing data and diagnostic output from models to be provided in NetCDF format.
Formats and, with help from PCMDI, software for producing output in the correct
format will be provided at the project host site.
Intercomparison workshop
The C4MIP Phase 1 workshop will take place in Hamburg on 18th-19th September
2003. All groups are encouraged to attend.
ANNEX 1: Forcing data
Global mean CO2: Ice core records and flask measurements (Rayner)
SSTs: HadISST1.1
Original dataset (monthly means) provided.
Groups may need to further process the data prior to input to the GCM to ensure that
time interpolation within the GCM does not alter the monthly means. Data processed
for use in the Hadley Centre model is available if applicable to other GCMs.
Land use:
Crops: annual fractional cover at 0.5 degree resolution from SAGE (Ramankutty and
Foley)
Pasture: locations of pasture as dominant land cover type at 0.5 degree resolution in
timeslices at 1900, 1950, 1970 and 1990 from RIVM (Klein Goldewijk).
Some processing was necessary for C4MIP (Betts):
Pasture was interpolated linearly in time to give annual fractional covers (assuming
either 0% or 100% cover in original timeslices). Pasture and/or crop fractions were
then modified to ensure that the 2 fractions do not sum to more than 1.0
Ocean carbon fluxes: median fluxes from OCMIP2
Fossil fuel emissions: Andres et al 1996
ANNEX 2: Locations of atmospheric CO2 observations
Station name
Bass Strait/Cape Grim
Bass Strait/Cape Grim
Bass Strait/Cape Grim
Bass Strait/Cape Grim
Bass Strait/Cape Grim
Bass Strait/Cape Grim
Bass Strait/Cape Grim
Alert, Greenland
Amsterdam Island
Ascension Island
Assekrem, Algeria
St. Croix, Virgin Is.
Azores
Baltic Sea, Poland
Baring Head St., NZ
Bermuda West
Barrow, Alaska
Black Sea, Romania
Carr, CO
Carr, CO
Lat
-40.38
-40.38
-40.38
-40.38
-40.38
-40.38
-40.38
82.45
-37.95
-7.92
23.18
17.75
38.75
55.50
-41.41
32.27
71.32
44.17
40.90
40.90
Long Elev.
Wind
144.39 500 SW NS
144.39 1500 SW NS
144.39 2500 SW NS
144.39 3500 SW NS
144.39 4500 SW NS
144.39 5500 SW NS
144.39 6500 SW NS
-62.52 210 SW
77.53 150
-14.42 54
5.42 2728
NS
-64.75
3
-27.08 30
16.67
7
174.87 80 S,SW
-64.88 30
-156.60 11 E,NE
28.68
3 NE
-104.80 3000
NS
-104.80 4000
NS
Topo
Carr, CO
Carr, CO
Cold Bay, Alaska
Cape Ferguson, Aust.
Cape Grim, Tasmania
Christmas Island
Mt. Cimone St., Italy
Cape Meares, OR
Cape Rama, India
Crozet, Indian Ocean
Cape St. James, Canada
Darwin, Australia
Easter Island
Estevan Pt, BC, Canada
Guam
Dwejra Pt., Malta
Halley Bay, Antarctica
Hungary
Storhofdi, Iceland
North Carolina
North Carolina
Canary Islands
Jubany St., Antarctica
Key Biscayne, FL
Kosan, Rep. of Korea
Kumukahi, Hawaii
Wisconsin tower
Wisconsin tower
Lampedusa, Italy
Mawson St., Antarctica
Mould Bay, Canada
Sand Island, Midway
Mauna Loa, Hawaii
Minamitorishima, Japan
Macquarie Island
Olympic Peninsula, WA
Plateau Rosa St., Italy
Palmer St., Antarctica
Qinghai Province, PRC
Ragged Pt., Barbados
Ryori St., Japan
Schauinsland, Germany
South China Sea
South China Sea
South China Sea
South China Sea
South China Sea
South China Sea
South China Sea
Sable Island, NS, Canada
40.90 -104.80 5000
NS
40.90 -104.80 6000
NS
55.20 -162.72 25
-19.28 147.06
2 E
-40.68 144.68 94 SW
1.70 -157.17
3
44.18 10.70 2165
NS
45.48 -123.97 30 W,NW
15.08 73.83 60 S,SE
-46.45 51.85 120
51.93 -131.02 89 W
-12.42 130.57
3 W,NW
-29.15 -109.43 50
49.38 -126.55 39 W
13.43 144.78
2
36.05 14.18 30
-75.67 -25.50 10
46.95 16.65 300
63.25 -20.15 100
35.35 -77.38 60
35.35 -77.38 500
NS
28.30 -16.48 2360
NS
-62.23 -58.82 15
25.67 -80.20
3 S
33.28 126.15 72
19.52 -154.82
3
45.93 -90.27 500
NS
45.93 -90.27 850
NS
35.52 12.62 85
-67.62 62.87 32
76.25 -119.35 58
28.22 -177.37
4
19.53 -155.58 3397
NS
24.30 153.97
8
-54.48 158.97 12
48.25 -124.42 488 W
45.93 7.70 3480
NS
-64.92 -64.00 10
36.27 100.92 3810
NS
13.17 -59.43
3
39.03 141.83 230 E
48.00 8.00 1205
NS
3.00 105.00 15
6.00 107.00 15
9.00 109.00 15
12.00 111.00 15
15.00 113.00 15
18.00 115.00 15
21.00 117.00 15
43.93 -60.02
5 E
Mahe Island, Seychelles
Shemya Island, Alaska
Shetland Is., Scotland
Samoa
South Pole
Atlantic Ocean, Norway
Pacific Ocean, Canada
Syowa, St., Antarctica
Tae-ahn Pen., Korea
Wendover, Utah
Ulaan Uul, Mongolia
Westerland, North Sea
Sede Boker, Israel
Zeppelin St., Norway
Adrigole, Ireland
Fraserdale, Ont, Canada
Kitt Peak, AZ
Lauder, NZ
Neumayer, Antarctica
Scripps Pier, CA
Table Mtn., CA
Trinidad Head, CA
-4.67
52.72
60.17
-14.25
-89.98
66.00
50.00
-69.00
36.73
39.90
44.45
55.00
31.13
78.90
52.00
49.88
31.90
-45.00
-71.60
32.83
34.40
41.05
55.17
174.10
-1.17
-170.57
-24.80
2.00
-145.00
39.58
126.13
-113.72
111.10
8.00
34.88
11.88
-10.00
-81.57
-111.60
169.70
-8.30
-117.27
-117.70
-124.15
3
40
30
42
2830
7
7
11
20
1320
914
8 W
400 NW
474
50 SW
210
2090
NS
370 S
16
14 W
2258
NS
109 W
Columns are
1 Name
2 Latitude
3 Longitude
4 Elevation (meters),
5 Wind : model sampling should be moved to the next gridcell
according to the given wind direction.
6 Topo: Topography of the site: NS means nonsurface so that we don't
believe the model has a hope of matching the topography and you should
pretend it's free atmosphere.