In the IPCC’s Fifth Assessment Report four scenarios describe future emissions, concentrations, and land-use. They are Representative Concentration Pathways (RCPs), the inputs to climate models that generate the IPCC’s projections. Strong mitigation policies lead to a low forcing level of 2.6 W/m2 by 2100 (RCP2.6). Two medium stabilization scenarios lead to intermediate outcomes in RCP4.5 and RCP6.0.
RCP8.5 gets the most attention, with its bold and dark assumptions (details here). It is a useful and important scenario, a warning of what might happen if the 21st century goes badly. It should spur us to act. Unfortunately, “despite not being explicitly designed as business as usual or mitigation scenarios” RCP8.5 has often been misrepresented as the “business as usual” scenario — becoming the basis for hundreds of predictions about our certain doom from climate change.
The result of this (part of a decade-long campaign) is widespread despair among climate scientists and more broadly, among Leftists. This misuse of RCP8.5 is a triumph of propaganda, but polls show its ineffectiveness (with climate change ranking at or near the bottom of public policy concerns). Yet each month brings more of the same.
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This useful scenario was hijacked to serve the apocalyptic visions of activists. Did this happen from scientists’ deliberate misrepresentation (a noble lie?) or carelessness? Who can say? Here are some examples of climate scientists misrepresenting RCP8.5.
Wrong from the beginning: “Compared to the scenario literature RCP8.5 depicts thus a relatively conservative business as usual case with low income, high population and high energy demand due to only modest improvements in energy intensity.” From “RCP 8.5: A scenario of comparatively high greenhouse gas emissions” by Keywan Riahi et al in Climate Change, November 2011.
“RCP8.5 assumes a ‘business-as-usual’ approach.” From a guide to AR5 WG1 by Carolyn Symon (PhD, environmental science), by Cambridge U (Sept 2013).
“The scenario with the most warming is the ‘business-as-usual’ RCP8.5, in which global mean temperature could be 4°C or more above pre-industrial times.” By*Matt Collins (Prof, Climate Systems at Exeter U) at Climatica, Dec 2013.
“Under a business as usual trajectory, the IPCC is saying 3.7 to 4.8 degrees by the end of this century“, said by Lesley Hughes (Prof Biology at Marcqarie U, lead author of WG2 in AR4 & AR5), March 2014.
Ottmar Edenhofer (Prof at the Potsdam Inst, Co-Chair of WG3 for AR5) describes RCP8.5 as the “business as usual” scenario at the IPCC AR5 WGIII press conference, 13 April 2014.
“What we see so far is that the only business-as-usual scenario among the RCPs is RCP8.5, a high-end business-as-usual scenario.” Said by John Nielsen-Gammon (Texas State Climatologist, Prof Atmospheric Sciences at Texas A&M), August 2014.
“for business-as-usual greenhouse gases (RCP8.5 scenario) …” — Said by James Hansen (climate scientists, Columbia Earth institute), July 2015.
“RCP8.5 is a scenario with unmitigated rise in greenhouse gas emissions.” — Said by Stefan Rahmstorf (Professor of Physics of the Oceans, Potsdam U) at RealClimate (Aug 2015). That’s true, but misleading by not mentioning the other assumptions.
