Representative Concentration Pathway

Representative Concentration Pathways (RCPs) are standardized scenarios of future greenhouse gas (GHG) concentrations and other radiative forcing agents, developed to facilitate integrated assessment of climate change. They are termed “representative” because they are not predictions but plausible pathways based on different assumptions about socioeconomic development, technology, and policy. Each RCP is defined by its radiative forcing level in the year 2100, measured in watts per square meter (W/m²). The four core RCPs—RCP2.6, RCP4.5, RCP6.0, and RCP8.5—span a range from a stringent mitigation scenario to a high-emissions baseline.¹

RCP2.6 is a stringent mitigation scenario that aims to keep global warming likely below 2°C above pre-industrial levels by 2100, requiring substantial and rapid emissions reductions. RCP4.5 and RCP6.0 are intermediate stabilization scenarios, with emissions peaking around mid-century and then declining, leading to radiative forcing stabilization at 4.5 and 6.0 W/m², respectively. RCP8.5 is a high-emissions baseline scenario with continued growth in GHG emissions, resulting in radiative forcing of 8.5 W/m² by 2100. These pathways were selected to represent a broad range of possible futures, from very low to very high emissions, and are used in climate models to project changes in temperature, precipitation, sea level, and other climate variables.²

The RCPs were developed by an international team of climate scientists and integrated assessment modelers, coordinated by the IPCC, and first published in 2011. They replaced the earlier SRES scenarios used in the Third and Fourth Assessment Reports. The RCPs were designed to be compatible with the latest climate models and to allow for a more systematic comparison of climate projections. They were formally adopted for use in the IPCC Fifth Assessment Report (AR5) in 2014, and have since been used extensively in climate research, including the Coupled Model Intercomparison Project Phase 5 (CMIP5) and Phase 6 (CMIP6).³

RCPs are used as input to global climate models (GCMs) and Earth system models (ESMs) to simulate future climate. They provide time series of GHG concentrations, emissions, and land-use changes, which drive the models' radiative forcing calculations. The resulting projections are used for impact assessments in sectors such as agriculture, water resources, and human health. RCPs also underpin the development of climate adaptation and mitigation strategies, as they allow policymakers to explore the consequences of different emissions pathways. For example, the difference in projected global mean temperature between RCP2.6 and RCP8.5 by 2100 is about 2.6°C, highlighting the importance of mitigation efforts.

Beyond the four core RCPs, there are extension scenarios that explore pathways beyond 2100, such as RCP2.6 extension and RCP8.5 extension, which are used for long-term climate projections. Additionally, RCPs are not purely greenhouse gas scenarios; they also include emissions of aerosols and other short-lived climate forcers, which have significant regional climate effects. A notable edge case is that RCP8.5 is often criticized as being an unrealistic “business-as-usual” scenario, yet it remains widely used for its high-end risk assessment. Another lesser-known fact is that the RCPs were designed to be compatible with the Shared Socioeconomic Pathways (SSPs), which were later developed to provide more detailed socioeconomic narratives, and the combination of RCPs and SSPs forms the basis of the latest IPCC scenarios.⁴

Radiative forcing

The change in energy flux in the atmosphere caused by natural or anthropogenic factors, measured in watts per square meter (W/m²).

CMIP5

Coupled Model Intercomparison Project Phase 5, a framework for coordinating climate model experiments.

SRES

Special Report on Emissions Scenarios, the previous set of scenarios used by the IPCC.

Shared Socioeconomic Pathways (SSPs)

Scenarios describing alternative socioeconomic developments, used in combination with RCPs for climate research.