Summary: Scientists and journalists bombard us with news about the coming climate catastrophe, described as certain unless we drastically change our economy. This has plunged many into despair. The hidden key to these forecasts is RCP8.5, the worst case scenario of the IPCC’s Fifth Assessment Report — often erroneously described as the “business as usual” scenario. Understanding this misuse of science reveals the weak basis of the most dire warnings (which set the mood at the Paris Conference), and helps explain why the US public assigns a low priority to fighting climate change despite the intense decades-long publicity campaign.
“We’re going to become extinct. Whatever we do now is too late.”
— Frank Fenner (Prof emeritus in microbiology at the Australian National U); Wikipedia describes his great accomplishments), an interview in The Australian, 10 June 2010.
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.
What future does RCP8.5 describe?
“In 2002, as I edited a book about global climate change, I concluded we had set events in motion that would cause our own extinction, probably by 2030. I mourned for months …”
— “Apocalypse or extinction?” by Guy McPherson (Prof Emeritus of Natural Resources and Ecology, U AZ), Oct 2009.
The papers describing the RCP’s clearly state their assumptions, unlike most of those that follow them. RCP8.5 describes a bleak scenario, a hot and dark world in 2100 (since it’s powered by coal, perhaps literally dark) — even before considering the effects of climate change. Below are the key points, with graphs from “The representative concentration pathways: an overview” by Detlef P. van Vuuren et al in Climatic Change, Nov 2011.
RCP8.5 assumes breaks in long-term trends for population growth and technological change, the opposite of the usual base case for planning. See this post for a more detailed look at it.