Representative Concentration Pathway (RCP) – a greenhouse gas concentration (not emissions) trajectory adopted by the IPCC. Four pathways were used for climate modeling and research for the IPCC's Fifth Assessment Report (AR5) in 2014. The pathways describe different climate futures, all of which are considered possible depending on the volume of greenhouse gases (GHG) emitted in the years to come. The RCPs – originally RCP2.6, RCP4.5, RCP6.0, and RCP8.5 – are labeled after a possible range of radiative forcing values in the year 2100 (2.6, 4.5, 6.0 and 8.5 W/m2 respectively). Radiative forcing describes the increase in energy content in the system with resulting rise in temperature. With the sixth update of the report (AR6), published between 2021 and 2023, the IPCC produced an updated set of five future climate projection scenarios, obtained by associating the RCPS to the Shared Socio-economic Pathways (SSP). These scenarios model climate response from 2015 to 2100 on the basis of a series of future emission scenarios that depend also on socio-economic hypotheses and climate mitigation levels. These five scenarios replace the previous Representative Concentration Pathways used in AR5 and are the following: • SSP1-1.9 and SSP2-2.6: scenarios associated with very low and low greenhouse gas emissions, respectively, in which CO2 emissions decrease to net zero around or after 2050. Mean global surface temperature is likely to be higher by 1.0°C-1.8°C in SSP1-1.9 and by 1.3°C-2.4°C in SSP2-2.6 by 2100 with respect to pre-industrial levels (1850-1900). • SSP2-4.5: scenario with a slower reduction of GHG emissions, in which carbon emissions remain more or less the same as today until about 2050. In this scenario, the increase in global surface temperature is in the range of 2.1°C to 3.5°C. • SSP3-7.0 and SSP5-8.5: scenarios associated with high and very high GHG emissions, respectively. In SSP3-7.0, CO2 emissions approximately double by 2100 with respect to current levels and global surface temperature is likely to increase by 2.8°C-4.6°C by the end of the century with respect to the pre-industrial period. In SSP5-8.5, instead, carbon emissions approximately double by 2050 and the increase in temperature is in the range of 3.3°C to 5.7°C.