In brief
At a glance
Quick Facts
- Current figure
- RCP2.6, 4.5, 6.0, 8.5 (radiative forcing in 2100: 2.6, 4.5, 6.0, 8.5 W/m²)
- Measurement date
- Defined in 2011; used in IPCC AR5 (2013-2014) and AR6 (2021)
- Previous figure
- SRES scenarios (2000) with A1, A2, B1, B2 families
- Change
- Simplified from 40 SRES scenarios to 4 RCPs; added policy-relevant forcing targets
- Data source
- IIASA RCP Database; IPCC AR5 and AR6; CMIP5/CMIP6 via ESGF
- Next update
- CMIP7 scenarios expected around 2025-2028; IPCC AR7 ~2029
Current figure
The current set of Representative Concentration Pathways (RCPs) comprises four scenarios: RCP2.6, RCP4.5, RCP6.0, and RCP8.5. Each is named after the approximate total radiative forcing in the year 2100 relative to 1750, expressed in watts per square meter (W/m²). Specifically, RCP2.6 corresponds to a peak forcing of ~3 W/m² before declining to 2.6 W/m² by 2100; RCP4.5 stabilizes at 4.5 W/m²; RCP6.0 stabilizes at 6.0 W/m²; and RCP8.5 reaches 8.5 W/m² by 2100. These pathways were first published in 2011 and have been used as the standard concentration scenarios in the Coupled Model Intercomparison Project Phase 5 (CMIP5) and the IPCC Fifth Assessment Report (AR5). For the Sixth Assessment Report (AR6, 2021), the RCPs were combined with Shared Socioeconomic Pathways (SSPs) to create a new scenario matrix, but the original RCPs remain foundational.
Measurement date
The RCPs were developed and formally published in a special issue of the journal Climatic Change in 2011 (van Vuuren et al., 2011). They were adopted by the IPCC for its Fifth Assessment Report, released in 2013–2014. As of 2025, the RCPs continue to be used in climate research, though they are now often paired with SSPs for CMIP6 and the IPCC AR6 (2021). The RCPs themselves are not updated on a regular schedule; they are fixed scenarios representing specific radiative forcing targets. However, the climate modeling community periodically develops new scenario sets for successive CMIP phases. The next major update is expected with CMIP7, anticipated around 2025–2028.
Previous figure
Before the RCPs, the standard emission scenarios were the SRES (Special Report on Emissions Scenarios), published in 2000 and used in the IPCC Third and Fourth Assessment Reports (2001, 2007). The SRES scenarios were organized into four families—A1, A2, B1, and B2—with a total of 40 individual scenarios. They spanned a wide range of possible futures, from rapid economic growth and globalization (A1) to regional fragmentation and slower technological change (A2). The highest-emission SRES scenario, A1FI, implied a radiative forcing of approximately 8.5 W/m² by 2100, similar to RCP8.5. The shift from SRES to RCPs represented a methodological change: from a sequential process (socioeconomic assumptions → emissions → concentrations → climate) to a parallel process where radiative forcing targets were chosen first, and then socioeconomic and emission pathways were developed to match them. This allowed for a more systematic exploration of climate outcomes and facilitated the integration of climate policy goals (e.g., the 2°C target).
Long-term trend
The development of emission scenarios has evolved over several decades, reflecting advances in integrated assessment modeling and changing policy contexts. The table below summarizes key scenario sets used in IPCC reports.
| Scenario set | Year published | IPCC report | Number of scenarios | Radiative forcing range in 2100 (W/m²) |
|---|---|---|---|---|
| IS92 | 1992 | SAR (1995) | 6 | ~4–8 |
| SRES | 2000 | TAR (2001), AR4 (2007) | 40 | ~2.5–8.5 |
| RCPs | 2011 | AR5 (2013–2014) | 4 | 2.6–8.5 |
| SSP-RCPs | 2017 | AR6 (2021) | 5 core (SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5) | 1.9–8.5 |
The RCPs marked a shift toward a more structured and policy-relevant set of pathways. The subsequent SSP-RCP framework added socioeconomic narratives, allowing for a richer analysis of mitigation and adaptation challenges. The long-term trend shows a move from a large number of exploratory scenarios to a smaller set of representative, well-characterized pathways that span the range of possible futures and are directly tied to radiative forcing outcomes.
Data source
The authoritative source for RCP data is the RCP Database, hosted by the International Institute for Applied Systems Analysis (IIASA) at https://tntcat.iiasa.ac.at/RcpDb. This database provides gridded emissions and concentrations for all four RCPs. The IPCC Assessment Reports (AR5 and AR6) are the primary synthesis documents that present and assess climate projections based on RCPs. The Coupled Model Intercomparison Project (CMIP) coordinates the climate model experiments; CMIP5 output is available via the Earth System Grid Federation (ESGF). For the SSP-RCP combinations used in AR6, the Scenario Model Intercomparison Project (ScenarioMIP) provides the data, also accessible through ESGF.
Methodology
RCPs are constructed using a reverse approach: a target radiative forcing level in 2100 is selected, and then integrated assessment models (IAMs) are used to derive internally consistent emission pathways for greenhouse gases, aerosols, and other radiatively active substances that achieve that forcing. The four RCPs were chosen to span the range of plausible future forcing, from a strong mitigation scenario (RCP2.6) to a high-emission baseline (RCP8.5). Each RCP was developed by a different modeling team using a different IAM: RCP8.5 (MESSAGE model), RCP6.0 (AIM model), RCP4.5 (GCAM model), and RCP2.6 (IMAGE model). The pathways include emissions of CO₂, CH₄, N₂O, and short-lived species like SO₂ and black carbon, as well as land-use changes. The resulting concentration and emission data are then used as input to global climate models (GCMs) to project future climate change. It is important to note that RCPs are not predictions; they are plausible scenarios that assume no specific climate policies beyond those already in place (for the higher RCPs) or assume aggressive mitigation (for RCP2.6).
Why annual values fluctuate
RCPs themselves are smooth, idealized pathways and do not exhibit year-to-year fluctuations. However, when comparing real-world emissions to RCP trajectories, annual fluctuations are observed due to short-term factors such as economic cycles, energy price volatility, weather patterns (e.g., affecting heating and cooling demand), and temporary policy changes. For example, global CO₂ emissions dipped during the 2008 financial crisis and the 2020 COVID-19 pandemic, but these dips do not alter the long-term RCP trajectories. The relevance of a particular RCP as a benchmark can shift over time as actual emissions evolve. In recent years, observed emissions have tracked closest to RCP8.5 in the short term, but long-term projections depend on future policy and technological developments. The RCP framework is designed to be robust to such short-term variability by focusing on century-scale forcing outcomes.
Regional variation
RCPs are global pathways, but their climate impacts vary significantly by region. Downscaling techniques and regional climate models (RCMs) are used to produce local projections. The table below shows projected global mean surface temperature changes by 2081–2100 relative to 1850–1900 for each RCP, based on the IPCC AR6 (2021). Regional temperature changes are generally larger over land and at high latitudes.
| RCP | Global mean temperature increase (°C) – best estimate (very likely range) | Arctic warming amplification | Precipitation change pattern |
|---|---|---|---|
| RCP2.6 | 1.3 (1.0–1.8) | 2–3 times global mean | Wet regions wetter, dry regions drier; monsoon variability |
| RCP4.5 | 2.7 (2.1–3.5) | 2–3 times global mean | Enhanced contrast; increased heavy precipitation in many regions |
| RCP6.0 | 3.0 (2.4–3.8) | 2–3 times global mean | Similar to RCP4.5 but more pronounced |
| RCP8.5 | 4.4 (3.3–5.7) | 3–4 times global mean | Strong wet/dry contrast; significant monsoon changes |
Source: IPCC AR6 WG1 SPM, Table SPM.1. Regional variations are further detailed in the IPCC Interactive Atlas (https://interactive-atlas.ipcc.ch).
Meaning and limitations
RCPs provide a consistent framework for exploring the climate consequences of different emission trajectories. They allow scientists to compare climate model results and assess risks under a range of possible futures. However, they have important limitations. First, RCPs are not forecasts; they do not assign probabilities to different outcomes. Second, the original RCPs did not include socioeconomic dimensions, which were later added via SSPs. Third, RCP8.5, often used as a “business-as-usual” scenario, has been criticized as implausibly high given recent trends in coal use and renewable energy deployment, though it remains a useful high-end benchmark. Fourth, the RCPs do not capture all possible feedbacks, such as permafrost carbon release, which could amplify warming. Finally, the pathways assume smooth transitions, whereas real-world policy and technology changes can be abrupt. Users should interpret RCP-based projections as “what-if” experiments rather than predictions.
Next expected update
The climate modeling community is currently preparing for the Coupled Model Intercomparison Project Phase 7 (CMIP7), which will underpin the IPCC Seventh Assessment Report (AR7). New scenarios are being developed under the ScenarioMIP activity. These are expected to include updated SSP-RCP combinations and possibly new “Shared Climate Policy Assumptions” (SPAs) that reflect the latest national pledges and net-zero targets. The timeline for CMIP7 is not yet finalized, but model runs are anticipated to begin around 2025–2026, with data becoming available in 2027–2028. The IPCC AR7 is tentatively scheduled for completion around 2029. Until then, the current RCPs and SSP-RCPs remain the standard reference pathways.
Downloadable chart or table
The table below summarizes the key characteristics of the four original RCPs, including their radiative forcing, CO₂-equivalent concentrations, and projected global warming from the IPCC AR6. The underlying data can be downloaded from the IIASA RCP Database (https://tntcat.iiasa.ac.at/RcpDb) and the IPCC AR6 WG1 data archive.
| RCP | Radiative forcing in 2100 (W/m²) | CO₂-eq concentration in 2100 (ppm) | Global mean temperature increase 2081–2100 vs. 1850–1900 (°C) – best estimate (very likely range) | Description |
|---|---|---|---|---|
| RCP2.6 | 2.6 | ~430 | 1.3 (1.0–1.8) | Peak-and-decline scenario; aggressive mitigation; likely limits warming to below 2°C |
| RCP4.5 | 4.5 | ~540 | 2.7 (2.1–3.5) | Stabilization scenario; intermediate mitigation |
| RCP6.0 | 6.0 | ~670 | 3.0 (2.4–3.8) | Stabilization scenario; higher baseline |
| RCP8.5 | 8.5 | ~935 | 4.4 (3.3–5.7) | High-emission scenario; no specific climate policy |
Note: CO₂-equivalent concentrations are approximate. Temperature ranges are from IPCC AR6 WG1 SPM, Table SPM.1, based on CMIP6 models. The RCP2.6 range reflects the updated assessment using the SSP1-2.6 scenario, which is comparable to the original RCP2.6.
FAQ
What are Representative Concentration Pathways (RCPs)?
Representative Concentration Pathways (RCPs) are greenhouse gas concentration trajectories adopted by the IPCC for climate modeling. They describe four possible climate futures based on different levels of radiative forcing—the change in energy balance caused by greenhouse gases and other agents—by the year 2100. The four RCPs are RCP2.6, RCP4.5, RCP6.0, and RCP8.5, named after the forcing level in W/m².
How many RCPs are there?
There are four original RCPs: RCP2.6, RCP4.5, RCP6.0, and RCP8.5. In the latest IPCC report (AR6), these were combined with Shared Socioeconomic Pathways (SSPs) to create additional scenarios, such as SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5, expanding the range of explored futures.
What is the difference between RCPs and SSPs?
RCPs specify the radiative forcing outcome (the physical climate change driver), while SSPs describe the socioeconomic conditions (population, economic growth, technology, policy) that lead to different emission levels. In CMIP6, RCPs and SSPs are combined: for example, SSP2-4.5 represents a 'middle-of-the-road' socioeconomic pathway that results in a radiative forcing of 4.5 W/m² by 2100.
Which RCP is most likely?
RCPs are not assigned probabilities, so no single RCP is considered 'most likely.' They are designed to span a range of plausible futures. Current policies and pledges, if fully implemented, are estimated to lead to a warming of around 2.5–3°C by 2100, which falls between RCP4.5 and RCP6.0. However, the actual trajectory depends on future decisions and technological developments.
What is RCP8.5?
RCP8.5 is the highest-emission scenario, reaching a radiative forcing of 8.5 W/m² by 2100. It assumes continued high population growth, slow technological change, and heavy reliance on fossil fuels, leading to a CO₂-equivalent concentration of about 935 ppm and a best-estimate warming of 4.4°C (3.3–5.7°C) by 2081–2100. It is often used as a 'business-as-usual' baseline, though some researchers argue it is increasingly implausible given current trends.
What is RCP2.6?
RCP2.6 is a 'peak-and-decline' scenario that represents strong mitigation. It requires global CO₂ emissions to peak by 2020 and decline to near zero by 2100, with net negative emissions thereafter. It results in a radiative forcing of 2.6 W/m² by 2100 and a best-estimate warming of 1.3°C (1.0–1.8°C), consistent with the Paris Agreement goal of limiting warming to well below 2°C.
How are RCPs used in climate models?
RCPs provide the time-varying concentrations of greenhouse gases, aerosols, and land-use changes that are used as input to global climate models (GCMs). The models then simulate the resulting changes in temperature, precipitation, sea level, and other climate variables. By running the same RCPs across many models, scientists can assess the range of possible climate responses and attribute uncertainties.
Are RCPs predictions?
No, RCPs are not predictions or forecasts. They are scenarios—plausible descriptions of how the future might unfold under specific assumptions. They do not incorporate probabilities and should not be interpreted as the most likely outcome. Instead, they are tools for exploring the consequences of different emission pathways and informing policy decisions.
What is the current RCP scenario?
There is no single 'current' RCP because they are all hypothetical. However, the observed global CO₂ emissions in recent years (2022–2024) have been tracking closest to the RCP8.5 trajectory in the short term, though long-term projections depend on future policies. The SSP2-4.5 scenario is often considered a 'middle-of-the-road' reference for current policy ambitions.
What is the next update for RCPs?
The next generation of scenarios is being developed for CMIP7, expected to begin model runs around 2025–2026. These will likely include updated SSP-RCP combinations and possibly new pathways reflecting the latest nationally determined contributions (NDCs) and net-zero pledges. The IPCC Seventh Assessment Report (AR7) is anticipated around 2029.
References
- van Vuuren, D.P., et al. (2011). The representative concentration pathways: an overview. Climatic Change, 109, 5–31. https://doi.org/10.1007/s10584-011-0148-z
- IPCC (2013). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report. Cambridge University Press.
- IPCC (2021). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report. Cambridge University Press. https://www.ipcc.ch/report/ar6/wg1/
- IIASA RCP Database. https://tntcat.iiasa.ac.at/RcpDb
- Eyring, V., et al. (2016). Overview of the Coupled Model Intercomparison Project Phase 6 (CMIP6) experimental design and organization. Geoscientific Model Development, 9, 1937–1958. https://doi.org/10.5194/gmd-9-1937-2016
