In 2005, four scenarios known as Representative Concentration Pathways (RCPs) were developed to inform the Intergovernmental Panel on Climate Change Assessment Report. The RCP scenarios, which include historical greenhouse gas emissions until 2005, are used in global climate models to project future emissions.
RCP 8.5 represents the highest theoretical use of fossil fuels, which would result in an additional 8.5 watts per square meter of radiative forcing by 2100.
RCP 8.5 has been dismissed by many experts as being a scare tactic that is unrealistic or misleading. However, a team including WHRC President Dr. Philip Duffy has now determined that RCP 8.5 is actually the closest approximation of both historical emissions and the expected outcomes of current global climate policies – tracking within one percent of actual emissions.
“Not only are the emissions consistent with RCP 8.5 in close agreement with historical total cumulative CO2 emissions, but RCP8.5 is also the best match out to mid-century under current and stated policies with still highly plausible levels of CO2 emissions in 2100,” wrote the study authors.
“Not using RCP8.5 to describe the previous 15 years assumes a level of mitigation that did not occur, thereby skewing subsequent assessments by lessening the severity of warming and associated physical climate risk.”
The researchers emphasized that while there are signs of progress on bending the global emissions curve and that our emissions picture may change significantly by 2100, focusing on the uncertain and distant future may distort the current debate on these issues.
“For purposes of informing societal decisions, shorter time horizons are highly relevant, and it is important to have scenarios which are useful on those horizons. Looking at mid-century and sooner, RCP8.5 is clearly the most useful choice,” wrote the experts.
“Given the agreement of 2005-2020 historical and RCP8.5 total CO2 emissions and the congruence between current policies and RCP8.5 emission levels to mid-century, RCP8.5 has continued utility, both as an instrument to explore mean outcomes as well as risk. Indeed, if RCP8.5 did not exist, we’d have to create it.”
The study is published in the journal Proceedings of the National Academy of Sciences.