Representative Concentration Pathways (RCPs) provide time-dependent projections of atmospheric greenhouse gas (GHG) concentrations. These GHG concentrations influence how much heat will be trapped in the upper atmosphere due to “radiative forcing” (basically, more solar radiation coming in than going out). The RCPs are numbered according to their level of radiative forcing, expressed as watts per meter squared: RCP2.6 (2.6 watts per meter squared forcing increase relative to pre-industrial conditions), RCP4.5, RCP6.0, and RCP8.5. The lower the RCP number, the less global warming.

There is no scientific consensus as to which RCP scenario is the most likely to occur. However, envisioned futures associated with RCP8.5 appear to get the most media attention. How can I tell? Although articles may not directly refer to RCPs, they often include links to the original research, which typically do indicate which RCP is being used to calculate the possible impact of climate change on humanity and the planet. For the really scary predictions, that would be RCP8.5.

RCP8.5 is a worst-case “no-mitigation” RCP that assumes no meaningful reduction in GHG emissions this century. Studies that use RCP8.5 to calculate the long-term effects of climate change often assume minimal adaptation to climate change as well, e.g., humanity doing little to increase the resilience of crops, coastal communities, cities, fisheries, coral reefs, wild habitat, etc. to the deleterious effects of a changing climate. RCP8.5 and the possible futures associated with RCP8.5 are sometimes referred to as the “business-as-usual” scenarios.

RCPs don’t come with socioeconomic storylines but they need to be compatible with plausible assumptions about economic development, energy consumption and land use patterns. In recent years RCP8.5 scenarios have come under criticism by a number of researchers for using emissions scenarios that involve a dramatic expansion of coal use. This when the global production and consumption of coal have been relatively flat for a number of years:

_2019 Coal -Global Production and Consumption.png

Unfortunately a lot of news articles about the catastrophic effects of climate change fail to mention the assumptions these predicted effects are based on. However, if you see “business-as-usual” in these articles, chances are they’re based on no-mitigation/little adaptation RCP8.5 scenarios.

Next: Looking at possible futures using plausible climate change scenarios.


Explainer: The high-emissions ‘RCP8.5’ global warming scenario Zeke Hausfather/Carbon Brief  August 21, 2019