A Representative Concentration Pathway (RCP) is a greenhouse gas concentration trajectory adopted by the IPCC for its fifth Assessment Report (AR5) in 2014. These four pathways are prominently considered in IPCC climate modelling and research, which describe different climate futures, all of which are considered possible depending on how much greenhouse gases are emitted in the years to come.

Pathway RCP4.5 is a scenario of long-term, global emissions of greenhouse gases, short-lived species, and land-use-land-cover which stabilizes global CO₂ atmospheric concentration at approximately 650 ppm CO2-equivalent, in the year 2100 without ever exceeding that value (Thomson et al., 2011).

Pathway RCP4.5 limits mid-century (2046–2065) global mean temperature increase to 1.4°C with a likely range of 0.9°C to 2.0°C (95% confidence interval). Moreover, it limits end-of-century (2081–2100) global mean temperature increase to 1.8°C with a likely range of 1.1°C to 2.6°C (95% confidence interval) (IPPC, 2013).

Over the 2020 to 2023 period (inclusive), the RCP4.5 corresponds to an average of 414.52 parts-per-million (ppm) of global CO₂ atmospheric concentration each year (Meinshausen et al. 2011). Over the 2024 to 2027 period, it corresponds to an average of 423.89 ppm of global CO₂ atmospheric concentration each year (ibid.).