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 IPPC 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.
Representative Concentration Pathway (RCP) 4.5 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 2022 to 2025 period (inclusive), the RCP4.5 corresponds to an average of 419.13 parts-per-million (ppm) of global CO₂ atmospheric concentration each year (Meinshausen et al. 2011). Over the 2027 to 2030 period, it corresponds to an average of 428.79 ppm of global CO₂ atmospheric concentration each year (ibid.).
What will the average global atmospheric CO₂ concentration be, over the 2020 to 2021 period (inclusive)?
This question resolves as the arithmetic mean of the "annual mean carbon dioxide (CO₂) concentration data from the Mauna Loa monitoring station" in 2020 and 2021, as reported by Earth System Research Laboratory.
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