8. Emergent constraints on carbon cycle feedbacks¶
8.1. Overview¶
Figures from Wenzel et al. (2014) are reproduced with namelist_wenz14jgr.xml. Variables relevant for the carbon cycle-climate feedback such as near surface air temperature (tas), net biosphere productivity (nbp) and (fgco2) are analyzed for coupled (1pctCO2; here the carbon cycle is fully coupled to the climate response) and uncoupled (esmFixCLim1; here the carbon cycle is uncoupled to the climate response) simulations. The standard namelist includes a comparison of cumulated nbp from coupled and uncoupled simulations and includes a set of routines to diagnose the long-term carbon cycle-climate feedback parameter (GammaLT) from an ensemble of CMIP5 models. Also included in the namelist is a comparison of the interannual variability of nbp and fgco2 for historical simulations used to diagnose the observable sensitivity of CO2 to tropical temperature changes (GammaIAV). As a key figure of this namelist, the diagnosed values from the models GammaLT vs. GammaIAV are compared in a scatter plot constituting an emergent constraint.
8.2. Available namelists and diagnostics¶
Namelists are stored in nml/
- namelist_wenzel14jgr.xml
Diagnostics are stored in diag_scripts/
- tsline.ncl: time line plots of annual means for spatial averages
- carbon_corr_2var.ncl: scatter plot of annual mean anomalies of two different variables; diagnosing and saving GammaIAV
- carbon_constraint.ncl: scatter plot of GammaLT vs. GammaIAV + line plot of probability density functions; diagnosing GammaLT
8.3. User settings¶
User setting files (cfg files) are stored in nml/cfg_carbon/
tsline (cfg_carbon_line.ncl, cfg_carbon_line_h.ncl)
Required diag_script_info attributes
- styleset: “CMIP5”
- ts_minlat: minimum latitude for area-averaging
- ts_maxlat: maximum latitude for area-averaging
- ts_minlon: minimum longitude for area-averaging
- ts_maxlon: maximum longitude for area-averaging
- multi_model_mean: True for multi-model mean calculation
- ts_maxyear: last year (time range)
- ts_minyear: first year (time range)
- time_avg: “yearly” (currently, only yearly is available)
- ts_anomaly: calculates anomalies with respect to the first 10-year average (anom, noanom)
- area_opper: type of area operation (average, sum)
ts_line (cfg_carbon_line_h.ncl)
Required diag_script_info attributes
- ts_detrend: detrend time series (detr, nodetr)
create_co2_flux.ncl, carbon_corr_2var.ncl
Required diag_script_info attributes
- styleset: “CMIP5”
- con_latrange: 2-element array of latitudes for time series plots if 2D or 3D
- con_lonrange: 2-element array of pressure levels for time series plots if 2D or 3D
- con_units: label string for units, e.g., “GtC/K”
- pcBGC: label for CMIP5 experiment (for creating filename mask), e.g., “esmFixClim1”
- reg_models: models to be included in emergent constraint (n-element array or (/”all”/)); note: has to be consistent with the list of models specified in the namelist!
8.4. Variables¶
- tas (atmos, monthly mean, longitude latitude time)
- co2 (atmos, monthly mean, plev longitude latitude time)
- nbp (land, monthly mean, longitude latitude time)
- fgco2 (ocean, monthly mean, longitude latitude time)
8.5. Observations and reformat scripts¶
Note: (1) obs4mips data can be used directly without any preprocessing; (2) see headers of reformat scripts for non-obs4mips data for download instructions.
- GCP - Global Carbon Budget including land (nbp) and ocean (fgco2) carbon fluxes
Reformat script: reformat_scripts/obs/reformat_obs_GCP.ncl
- NCEP - National Centers for Environmental Prediction reanalysis data for near surface temperature
Reformat script: reformat_scripts/obs/reformat_obs_NCEP.ncl
8.6. References¶
- Cox, P. M., D. B. Pearson, B. B. Booth, P. Friedlingstein, C. C. Huntingford, C. D. B. Jones, and C. M. Luke, 2013, Sensitivity of tropical carbon to climate change constrained by carbon dioxide variability, Nature, 494(7437), 341–344. doi: 10.1038/nature11882
- Wenzel, S., P. M. Cox, V. Eyring, and P. Friedlingstein, 2014, Emergent Constraints on Climate Carbon Cycle Feedbacks in the CMIP5 Earth System Models, JGR Biogeoscience, 119(5), doi: 2013JG002591.