The Radiative Forcing Model Intercomparison Project defines standard simulations to quantify Effective Radiative Forcing (ERF) and its components across climate models.
Inferring effective radiative forcing from global model integrations
The RFMIP2.0 protocol, like its predecessor, includes a suite of fixed sea-surface-temperature 30-year time-slice experiments to robustly diagnose the ERF for a given perturbation, and a suite of fixed sea-surface-temperature transient experiments extending from 1850–2100, used to diagnose the time evolution of the ERF. Fixing sea-surface temperatures and sea-ice conditions suppresses climate feedbacks and allows ERF to be diagnosed as the difference in top-of-atmosphere radiation fluxes between each experiment and the piClim-control run (Forster et al., 2016). Experiments are ranked into tiers to emphasize their priority level.
1. Tier 1 and Tier 2 core RFMIP2.0 experiments
Three legacy RFMIP experiments are now part of the CMIP7 DECK — while no longer technically RFMIP experiments, they remain crucial to the project and are treated as Tier 1 here. Some RFMIP experiments are also part of the CMIP7 Assessment Fast Track (AFT).
| Tier | Experiment ID | Description / forcing | SST / sea ice condition | Min. length |
|---|---|---|---|---|
| Tier 1 · DECK | piClim-control | Baseline pre-industrial atmospheric state | Climatological 1850 SSTs | 30 years |
| Tier 1 · DECK | piClim-4xCO2 | Abrupt 4× CO₂ concentration increase | Climatological 1850 SSTs | 30 years |
| Tier 1 · DECK | piClim-anthro | All present-day (2021) anthropogenic forcings combined | Climatological 1850 SSTs | 30 years |
| Tier 1 · AFT | piClim-aer | Anthropogenic aerosols at present-day (2021) levels | Climatological 1850 SSTs | 30 years |
| Tier 1 | piClim-ghg | Well-mixed greenhouse gases at present-day (2021) levels | Climatological 1850 SSTs | 30 years |
| Tier 1 | piClim-lu | Present-day (2021) land use / land cover changes | Climatological 1850 SSTs | 30 years |
| Tier | Experiment | Description | Start | End | Major purpose |
|---|---|---|---|---|---|
| Tier 1 · AFT | piClim-histall | Time-varying forcing from all agents | 1850 | 2100 | Diagnose transient ERF from all agents |
| Tier 1 · AFT | piClim-histaer | Time-varying ERF from aerosols (ozone fixed at pre-industrial concentrations) | 1850 | 2100 | Diagnose transient ERF from aerosols (ozone fixed at pre-industrial) |
| Tier 2 | piClim-histnat | Time-varying ERF from volcanoes, solar (incl. spectral) variability, etc. | 1850 | 2100 | Diagnose transient natural ERF |
| Tier 2 | piClim-histghg | Time-varying ERF from non-ozone (well-mixed) greenhouse gases | 1850 | 2100 | Diagnose transient ERF from non-ozone GHGs |
2. Tier 3 RFMIP2.0 experiments
Tier 3 consists of new fixed-SST time-slice experiments to study the linearity of radiative forcing, the sensitivity of radiative forcing to the underlying base state, and the contribution of land effects to the diagnosis of radiative forcing.
| Tier | Experiment ID | Description / forcing | SST / sea ice condition | Min. length |
|---|---|---|---|---|
| Tier 3 | piClim-p4K | Pre-industrial (1850) conditions with SSTs uniformly 4K warmer | Uniformly 4K warmer than pre-industrial | 30 years |
| Tier 3 | piClim-p4K-4xCO2 | 4× CO₂ with SSTs uniformly 4K warmer than pre-industrial | Uniformly 4K warmer than pre-industrial | 30 years |
| Tier 3 | piClim-p4K-aer | Present-day (2021) aerosols with SSTs uniformly 4K warmer than pre-industrial | Uniformly 4K warmer than pre-industrial | 30 years |
| Tier | Experiment ID | Description / forcing | SST / sea ice condition | Min. length |
|---|---|---|---|---|
| Tier 3 | piClim-0.5xCO2 | CO₂ concentrations set to half of pre-industrial | Climatological 1850 SSTs | 30 years |
| Tier 3 | piClim-2xCO2 | CO₂ concentrations set to 2× pre-industrial | Climatological 1850 SSTs | 30 years |
| Tier 3 | piClim-4xCO2-bgc | CO₂ at 4× pre-industrial, applied only to the carbon cycle | Climatological 1850 SSTs | 30 years |
| Tier 3 | piClim-4xCO2-rad | CO₂ at 4× pre-industrial, applied only to radiation | Climatological 1850 SSTs | 30 years |
| Tier | Experiment ID | Description / forcing | SST / sea ice condition | Min. length |
|---|---|---|---|---|
| Tier 3 | piClim-FixedLST | Pre-industrial (1850) conditions with land-surface temperatures fixed from piClim-control | Climatological 1850 SSTs (fixed LST) | 30 years |
| Tier 3 | piClim-FixedLST-4xCO2 | 4× CO₂ with land-surface temperatures fixed at pre-industrial | Climatological 1850 SSTs (fixed LST) | 30 years |
| Tier 3 | piClim-FixedLST-anthro | Present-day (2021) anthropogenic forcing (GHGs, aerosols, land use) with land-surface temperatures fixed at pre-industrial | Climatological 1850 SSTs (fixed LST) | 30 years |
| Tier 3 | piClim-FixedLST-aer | Present-day (2021) anthropogenic aerosols with land-surface temperatures fixed at pre-industrial | Climatological 1850 SSTs (fixed LST) | 30 years |
| Tier 3 | piClim-FixedLST-ghg | Present-day (2021) well-mixed greenhouse gases only (non-ozone) with land-surface temperatures fixed at pre-industrial | Climatological 1850 SSTs (fixed LST) | 30 years |
| Tier 3 | piClim-FixedLST-lu | Present-day (2021) land use with land-surface temperatures fixed at pre-industrial | Climatological 1850 SSTs (fixed LST) | 30 years |
Lineage
RFMIP2.0 extends the original RFMIP protocol designed for CMIP6 by Pincus, Forster & Stevens (2016), carrying its fixed-SST approach forward with an updated design for the CMIP7 ensemble.
See full protocol details in Kramer et al., 2026.