The plausibility of emissions levels as high as the emissions scenario conventionally associated with the RCP8.5 and SSP5-8.5 concentration pathways has been called into question since AR5, as has the emissions pathway feasibility of the low scenarios . However, these views are contested  It is important to realise that emissions scenarios and concentration pathways are not the same thing and higher concentration pathways, such as RCP8.5 could arise from lower emissions scenarios if carbon cycle feedbacks are stronger than assumed in the integrated assessment models  used to create the standard scenarios . In the majority of full-complexity Earth System Models, these feedbacks are stronger than in the IAMs , so the RCP8.5 concentration pathway cannot be ruled out purely through consideration of the economic aspects of emissions scenarios. Nonetheless, the likelihood of a climate outcome, and the overall distribution of climate outcomes, are a function of the emissions scenario's likelihood. Note that the original RCPs were created explicitly to facilitate a broad range of climate modelling experiments, with the expectation that other issues, such as socioeconomic uncertainty, could be subsequently explored .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report