Table of Contents
Summarised by Centrist
The Daily Sceptic’s Chris Morrison reports that a group responsible for developing climate scenarios for the IPCC and wider research community has described the long-used RCP8.5 pathway assumptions as “implausible”.
RCP8.5 stands for “Representative Concentration Pathway 8.5”. The “8.5” refers to 8.5 watts per square metre of additional heat energy projected to be trapped in the Earth’s atmosphere by 2100 compared with pre-industrial levels. In simple terms, it was a worst-case climate scenario used in computer models to estimate what could happen if greenhouse gas emissions kept rising sharply.
Morrison cites climate policy writer Roger Pielke Jr, who wrote: “The scenarios that have dominated climate research, assessment and policy during the past two cycles of the IPCC assessment process are implausible.” Pielke also said they “describe impossible futures”.
RCP8.5 has often been used as a high-emissions scenario in climate modelling. Morrison writes that it has fed into “tens of thousands of research papers” and many media reports, while governments and international organisations have used such scenarios in policy and regulation.
RCP8.5 models projected warming of about 4 °C by 2100 from an 1850-1900 baseline.
Morrison also notes disagreement over whether researchers had already moved away from RCP8.5. He cites climate researcher Zeke Hausfather saying the research community had “moved on”, but Pielke argued Google Scholar still showed 16,900 articles using RCP8.5 in the following three-year period.
New high-end pathways for future IPCC modelling may still produce a projected 3 °C of warming by 2100, down from 3.9 °C under the previous high scenario, according to Pielke’s figures.
Morrison argues the change raises questions about media stories and policy decisions based on the older high-emissions scenario.
