Zero Emissions Commitment (ZEC)#

Overview#

The Zero Emissions Commitment (ZEC) quantifies the change in global mean temperature expected to occur after net carbon dioxide (CO2) emissions cease. ZEC is therefore important to consider when estimating the remaining carbon budget. Calculation of ZEC requires dedicated simulations with emissions set to zero, branching off a base simulation with emissions. In CMIP6 the simulations were part of ZECMIP, with the simulations called esm-1pct-brch-xPgC branching off the 1pctCO2 simulation when emissions reach x PgC. The default x was 1000PgC, with additional simulations for 750PgC and 2000PgC. In CMIP7, ZEC simulations (esm-flat10-zec) are part of the fast track and branch off (esm-flat10) with constant emissions of 10GtC/yr at year 100 (Sanderson 2024).

Available recipes and diagnostics#

Recipes are stored in recipes/

  • recipe_zec.yml

Diagnostics are stored in diag_scripts/

User settings in recipe#

Note: The preprocessor settings should not be changed. When changing the recipe, ensure that the reference simulation period (generally 1pctCO2 or esm-flat10, using the anomaly_base preprocessor block) is the 20-year period around the time the ZEC simulation branches off of. This point may vary in CMIP6 for 1pctCO2, while in CMIP7 it should be at year 100 of esm-flat10.

  • Preprocessor

    • area_statistics (operation: mean): Calculate global mean.

    • annual_statistics (operation: mean): For the ZEC simulation, compute annual statistics.

    • climate_statistics (operation: mean, period: full): For the reference simulation, compute the 20-year time average centered around the time when the ZEC simulation starts.

  • Script climate_metrics/zec.py

    • zec_year, list, optional (default: [50]): Calculate ZEC for the 20-year average centered around year x, multiple values are possible. Barplots are generated for all ZECx.

    • experiments, dict, optional: When using non-default experiments to calculate ZEC, the experiment setting is required with values for reference and simulation. Accepted by default are: reference: esm-flat10, 1pctCO2 simulation: esm-flat10-zec, esm-1pct-brch-1000PgC

Variables#

  • tas (atmos, monthly, longitude, latitude, time)

Observations and reformat scripts#

None

References#

  • MacDougall, A. H., Frölicher, T. L., Jones, C. D., Rogelj, J., Matthews, H. D., Zickfeld, K., Arora, V. K., Barrett, N. J., Brovkin, V., Burger, F. A., Eby, M., Eliseev, A. V., Hajima, T., Holden, P. B., Jeltsch-Thömmes, A., Koven, C., Mengis, N., Menviel, L., Michou, M., Mokhov, I. I., Oka, A., Schwinger, J., Séférian, R., Shaffer, G., Sokolov, A., Tachiiri, K., Tjiputra, J., Wiltshire, A., and Ziehn, T.: Is there warming in the pipeline? A multi-model analysis of the Zero Emissions Commitment from CO2, Biogeosciences, 17, 2987–3016, https://doi.org/10.5194/bg-17-2987-2020, 2020.

  • Sanderson, B. M., Brovkin, V., Fisher, R., Hohn, D., Ilyina, T., Jones, C., Koenigk, T., Koven, C., Li, H., Lawrence, D., Lawrence, P., Liddicoat, S., Macdougall, A., Mengis, N., Nicholls, Z., O’Rourke, E., Romanou, A., Sandstad, M., Schwinger, J., Seferian, R., Sentman, L., Simpson, I., Smith, C., Steinert, N., Swann, A., Tjiputra, J., and Ziehn, T.: flat10MIP: An emissions-driven experiment to diagnose the climate response to positive, zero, and negative CO2 emissions, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-3356, 2024.

Example plots#

../_images/zec_ts.png

Fig. 176 Time series of ZEC - temperature change after cessation of emissions.#

../_images/zec_bar.png

Fig. 177 Barplot for ascending values of Zecx, with x = 50 in this case, symbolizing the Zero Emissions Commitment 50 years after emissions cease.#