The study presents greenhouse gas (GHG) concentrations for the Representative Concentration Pathways (RCPs) and their extensions beyond 2100, known as Extended Concentration Pathways (ECPs). These projections include major anthropogenic GHGs and are based on multi-year efforts to develop new climate change scenarios. Historical GHG concentrations from 1750–2005 are combined with harmonized emissions from four Integrated Assessment Models (IAMs) for 2005–2100. The RCPs are based on different emission scenarios, and their concentrations are influenced by future climate feedbacks. The study uses the MAGICC6 model to project temperature increases, ranging from 1.5°C by 2100 for RCP2.6 to 4.5°C for RCP8.5 relative to pre-industrial levels. Beyond 2100, ECPs are simple extensions of RCPs, assuming either stabilized concentrations or constant emissions. For example, RCP2.6 is extended with constant emissions leading to CO₂ concentrations of 360 ppm by 2300. The study also presents one supplementary extension, illustrating the implications of returning to ECP4.5 levels by 2250. Radiative forcing values are provided for the RCPs and ECPs. The study discusses the harmonization of emissions and concentrations, the use of MAGICC6 for deriving GHG concentrations, and the implications of different emission scenarios. The results show that the RCPs span a wide range of radiative forcing levels, with RCP8.5 having the highest. The study concludes that the RCPs and ECPs provide a common set of input data for climate model comparisons, reflecting middle-of-the-road carbon cycle and climate model responses. The study highlights the importance of considering cumulative emissions and the long-term impacts of GHG concentrations on climate. The limitations of the study include uncertainties in future OH concentrations, CH₄ lifetimes, N₂O concentrations, and the effect of including a nitrogen cycle. The study emphasizes the need for further research to refine these projections and improve the accuracy of climate models.The study presents greenhouse gas (GHG) concentrations for the Representative Concentration Pathways (RCPs) and their extensions beyond 2100, known as Extended Concentration Pathways (ECPs). These projections include major anthropogenic GHGs and are based on multi-year efforts to develop new climate change scenarios. Historical GHG concentrations from 1750–2005 are combined with harmonized emissions from four Integrated Assessment Models (IAMs) for 2005–2100. The RCPs are based on different emission scenarios, and their concentrations are influenced by future climate feedbacks. The study uses the MAGICC6 model to project temperature increases, ranging from 1.5°C by 2100 for RCP2.6 to 4.5°C for RCP8.5 relative to pre-industrial levels. Beyond 2100, ECPs are simple extensions of RCPs, assuming either stabilized concentrations or constant emissions. For example, RCP2.6 is extended with constant emissions leading to CO₂ concentrations of 360 ppm by 2300. The study also presents one supplementary extension, illustrating the implications of returning to ECP4.5 levels by 2250. Radiative forcing values are provided for the RCPs and ECPs. The study discusses the harmonization of emissions and concentrations, the use of MAGICC6 for deriving GHG concentrations, and the implications of different emission scenarios. The results show that the RCPs span a wide range of radiative forcing levels, with RCP8.5 having the highest. The study concludes that the RCPs and ECPs provide a common set of input data for climate model comparisons, reflecting middle-of-the-road carbon cycle and climate model responses. The study highlights the importance of considering cumulative emissions and the long-term impacts of GHG concentrations on climate. The limitations of the study include uncertainties in future OH concentrations, CH₄ lifetimes, N₂O concentrations, and the effect of including a nitrogen cycle. The study emphasizes the need for further research to refine these projections and improve the accuracy of climate models.