RCPs

Representative Concentration Pathways (RCPs) are greenhouse gas concentration trajectories used for climate research. They describe how atmospheric GHG concentrations and related radiative forcing might evolve over time, independent of specific policy choices. They were developed for use in climate model experiments and to replace earlier SRES scenarios. They are used with global climate models to project future climate under different concentration pathways.

There are four commonly cited RCPs: RCP2.6, RCP4.5, RCP6.0, and RCP8.5. By the year 2100, their total radiative forcing values are 2.6, 4.5, 6.0, and 8.5 watts per square meter, respectively. RCP2.6 assumes aggressive mitigation leading to near-zero or negative emissions in some regions, with early peak and decline. RCP4.5 stabilizes around mid-century. RCP6.0 assumes moderate to high emissions with stabilization later in the century. RCP8.5 represents a high-emissions pathway with continued growth in fossil fuel use.

In IPCC assessments, the four RCPs were used in CMIP5 climate model experiments to project temperature, precipitation, and other climate variables. They have since been extended into the concept of SSPs (Shared Socioeconomic Pathways) and used in CMIP6 as SSP-RCP combinations that pair socio-economic futures with concentration pathways.

Limitations: RCPs are scenarios of concentration trajectories rather than policy prescriptions; they rely on model assumptions about emissions, land use, technology, and energy mix. Real-world outcomes depend on policy, technology, and behavior, and actual trajectories may diverge from any single RCP.