3. Control Simulation

In order to quantify climate drift, we require a control run from all models with atmospheric CO2 forcing held constant at 280 ppm, with an integration time of 1156 years. Please provide all output as specified on the Submissions page. An additional control simulation with freely evolving CO2 (zero emissions) is requested for models with an active coupled carbon cycle that will participate in experiments looking at the response of CO2 to historical forcing.

4. Historical Simulations

Initialize with an equilibrium spin up at year January 1, 850 AD. Undertake a suite of 1156-year simulations until December 31, 2005 AD using the forcing provided at: /http://climate.uvic.ca/EMICAR5/forcing The simulations over the last millennium will follow the PMIP3/CMIP5 protocol. Further details are available from Schmidt et al. (2010) and: https://pmip3.lsce.ipsl.fr/wiki/doku.php/pmip3:design:lm:final.

Each simulation will apply changes in only one forcing component at a time. An additional simulation will include all forcings varying simultaneously. The difference between the "Total" forcing simulation (TOT in Figure 1) and the sum of the individual forcing simulations will indicate the extent to which global mean surface air temperature response is linear. This will be examined for each model.

Anthropogenic Forcing Fig. 1 Natural Forcing Fig. 1
CO2 CO2 CO2 (preindustrial) CO2
Additional Greenhouse Gases AGG Additional Greenhouse Gases (preindustrial) AGG
Land Use Changes LND Solar SOL
Sulphate Aerosols SUL Volcanic VOL
    Orbital ORB

Figure 1: Example of a 1000 year historical simulation from the UVic ESCM. The TOT curve is the annually-averaged global mean surface air temperature (SAT) arising from an experiment driven by changes in all forcing. The NON curve represents the control experiment of section 3. Each of the other curves shows the annually-averaged global mean SAT response when the UVIc model is forced by changes in only one component of the radiative forcing (see Table 1 for definitions).

Freely Evolving CO2 Response: Optional "Natural" and "Total" (Natural + Anthropogenic) forcing simulations with freely evolving atmospheric CO2 are requested for models with an active coupled carbon cycle. Externally applied CO2 emissions should be zero for the "Natural" forcing simulation. Forcing from changes in other trace gases, aerosols and land use change should be also be set to zero. Do not include any contribution to CO2 from the modelled oxidation of methane. For the "Total" forcing simulation, historical anthropogenic CO2 emissions should be specified. Land use emissions may be included if the model does not explicitly calculate them from anthropogenic land cover changes. All forcing, other than CO2, should be the same as for the "Total" simulation with specified CO2 described above.

Last Millennium Forcing Reference: Schmidt, G.A., J. H. Jungclaus, C. M. Ammann, E. Bard, P. Braconnot, T. J. Crowley, G. Delaygue, F. Joos, N. A. Krivova, R. Muscheler, B. L. Otto-Bliesner, J. Pongratz, D. T. Shindell, S. K. Solanki, F. Steinhilber, and L. E. A. Vieira, 2010: Climate forcing reconstructions for use in PMIP simulations of the last millennium (v1.0). Geosci. Model Dev. Discuss., 3, 1549-1586

5. Representative Concentration Pathways

Representative Concentration Pathways (RCPs) have been designed to provide radiative forcing data for modelling groups wishing to contribute to the IPCC AR5. Information on the RCPs is available here. The Coupled Modelling Intercomparison Project (CMIP) have taken the RCP data and designed a suite of experiments for the CMIP5 project. See Taylor et al. (2009) and http://www-pcmdi.llnl.gov/ for details.

CMIP5 Experimental Design Reference: Taylor, K. E., R. J. Stouffer and G. A. Meehl, 2009: A Summary of the CMIP5 Experiment Design

Contributing EMICs are asked to undertake the following experiments:

5.1 RCP extensions - CO2 concentration commitment

Starting from the year 2005 initial condition obtained using TOT forcing in 4 above, each of the four RCPs together with their extensions are to be carried our to year 2300. The atmospheric CO2 concentration is to be specified and all other greenhouse gas and aerosol forcing are to be included as radiative forcing following RCP specifications. EMICs with a carbon cycle will diagnose implied emissions. From 2300-3000 radiative forcing and atmospheric CO2 concentration will r emain constant at their 2300 values.
  a.   RCP2.6:   2006-3000
  b.   RCP4.5:   2006-3000
  c.   RCP6:     2006-3000
  d.   RCP8.5:   2006-3000

5.2 RCP extensions - CO2 emissions commitment

These experiments are the same as in 5.1 up to year 2300. Implied CO2 emissions over the last decade of the RCP integrations (years 2290-2300) are diagnosed. These emissions are then held fixed from 2300 onwards. Radiative forcing for other greenhouse gases and aerosols are also remained fixed at 2300.

5.3 RCP extensions - CO2 climate commitment

These experiments are the same as in 5.1 up to year 2300. Implied CO2 emissions over the last decade of the RCP integrations (years 2290-2300) are diagnosed. Implied CO2 emissions are also determined from years 1840-1850 of the historical Total simulation. The difference between these two diagnosed emissions is termed the "anthropogenic perturbation". At 2300 the anthropogenic perturbation is set to zero. This means that CO2 emissions are set to the 1840-1850 diagnosed values. Radiative forcing for other greenhouse gases and aerosols are also held fixed at 2300.

5.4 RCP extensions - Climate commitment

These experiments are the same as in 5.3 except that at year 2300, the radiative forcing for other anthropogenic greenhouse gases and aerosols is also set to 1840-1850 average levels.

5.5 RCP extensions - Irreversibility

Starting from year 3000 for each of the RCP extensions in 5.1, continue on from 3000 to 4000 with CO2 concentration:
  1. linearly decreasing to preindustrial level in 100 years.
  2. linearly decreasing to preindustrial level in 1000 years.
  3. allowed to freely evolve (zero emissions), with atmospheric CO2 concentrations being determined by the model's carbon cycle.

6. Idealized experiment to 2 x CO2 and atmospheric lifetime

Starting from the end of the preindustrial control run of 3, impose an instantaneous (i.e. within a single timestep) increase of atmospheric CO2 to 560 ppmv and hold it fixed for 1000 years.

7. Idealized experiment to 4 x CO2 and atmospheric lifetime

Each of the following experiments are 1000 years long and start from the end of the preindustrial control run of 3. Experiments "e" and "f" are designed to understand carbon cycle / climate feedbacks.

  1. Impose an instantaneous increase of atmospheric CO2 to 1120 ppmv and hold it fixed.
  2. Instantaneously increase the atmospheric CO2 concentration to 1120 ppmv and allow it to evolve.
  3. Increase CO2 at 1 % per year until 4 x CO2 (1120 ppmv) is reached and hold fixed thereafter. We will compute the Transient Climate Response (TCR) at 2 x CO2 and 4 x CO2 from this model output.
  4. Increase CO2 at 1 % per year until 4 x CO2 is reached. Then let atmospheric CO2 evolve freely.
  5. Repeat c but the radiation code sees atmospheric CO2 fixed at 280 ppm.
  6. Repeat c but only the radiation code sees the increasing atmospheric CO2.

    Optional (constant emissions)
  7. Increase CO2 at 1 % per year until 4 x CO2 (1120 ppmv) is reached. Diagnose the average emissions over the previous year (simulation year 137.863 to 138.863) and apply these as constant emissions until the end of the simulation.

8. Allowable cumulative emissions

For these simulations, only EMICs coupled to a dynamic carbon cycle component are appropriate. As an additional requirement, the carbon cycle component must also be published in the refereed literature and references (and pdfs) need to be provided with the model description (see requirements).

Allowable cumulative emissions of CO2 are to be computed for four temperature stabilization profiles (Figure 2). The methodology of Zickfeld et al. (2009) will be followed for this intercomparison. This will involve the implementation of "temperature tracking" as described in the Materials and Methods section of Zickfeld et al. (2009). Simple sample code detailing how this is done has been made available at:
http://climate.uvic.ca/EMICAR5/forcing

The temperature tracking procedure will likely need to be calibrated for each EMIC. Please see sample EMIC calibration curves in Figure 3 (which should be submitted separately).


Figure 2: Temperature stabilization profiles for 1.5, 2, 3 and 4C.


Figure 3: Validation of temperature tracking procedure over the historical period 1800-2000. Top: globally-averaged surface air temperature. Bottom: atmospheric CO2 concentration. The blue curve indicates a specified CO2 experiment. The red curve indicates a specified temperature experiment.

Temperature Tracking Reference: Zickfeld, K., M. Eby, H.D. Matthews and A.J. Weaver, 2009: Setting cumulative emissions targets to reduce the risk of dangerous climate change. Proceedings of the National Academy of Sciences, 38, 16129-16134.