The paper presents the Representative Concentration Pathways (RCPs) and their extensions beyond 2100, the Extended Concentration Pathways (ECPs), for greenhouse gas (GHG) concentrations. These projections include all major anthropogenic GHGs and are derived from a multi-year effort to produce new scenarios for climate change research. The authors combine atmospheric concentration observations and emissions estimates for historical periods (1750-2005) with harmonized emissions projected by four different Integrated Assessment Models (IAMs) for 2005-2100. The concentrations are influenced by future climate itself due to feedbacks in the carbon and other gas cycles, which are emulated using the reduced-complexity carbon cycle climate model MAGICC6. The projected 'best-estimate' global-mean surface temperature increases range from 1.5°C by 2100 for the lowest RCP (RCP2.6) to 4.5°C for the highest (RCP8.5), relative to pre-industrial levels. Beyond 2100, the ECPs are simple extensions of the RCPs, assuming either smooth stabilization of concentrations or constant emissions. The lower RCP2.6 pathway represents a strong mitigation scenario, leading to CO2 concentrations returning to 360 ppm by 2300. The paper also presents supplementary extensions to illustrate stringent emissions implications, such as returning to ECP4.5 concentration levels by 2250 after high emissions during the 21st century. The study provides a reference starting point for further analysis in model intercomparison exercises, focusing on the relationship between emissions and concentrations.The paper presents the Representative Concentration Pathways (RCPs) and their extensions beyond 2100, the Extended Concentration Pathways (ECPs), for greenhouse gas (GHG) concentrations. These projections include all major anthropogenic GHGs and are derived from a multi-year effort to produce new scenarios for climate change research. The authors combine atmospheric concentration observations and emissions estimates for historical periods (1750-2005) with harmonized emissions projected by four different Integrated Assessment Models (IAMs) for 2005-2100. The concentrations are influenced by future climate itself due to feedbacks in the carbon and other gas cycles, which are emulated using the reduced-complexity carbon cycle climate model MAGICC6. The projected 'best-estimate' global-mean surface temperature increases range from 1.5°C by 2100 for the lowest RCP (RCP2.6) to 4.5°C for the highest (RCP8.5), relative to pre-industrial levels. Beyond 2100, the ECPs are simple extensions of the RCPs, assuming either smooth stabilization of concentrations or constant emissions. The lower RCP2.6 pathway represents a strong mitigation scenario, leading to CO2 concentrations returning to 360 ppm by 2300. The paper also presents supplementary extensions to illustrate stringent emissions implications, such as returning to ECP4.5 concentration levels by 2250 after high emissions during the 21st century. The study provides a reference starting point for further analysis in model intercomparison exercises, focusing on the relationship between emissions and concentrations.