Fernando Leanme has been all over the RCP 8.5 story. He’s commented on it here frequently but also at his own blog, a blog with a great masthead picture. Even if you don’t agree with Fernando or myself, it’s worth a look.
Representative Concentration Pathways replace the IPCC’s Special Report on Emission Scenarios (SRES). There are four RCPs named after the additional forcing in watts per square meter they are anticipated to have by 2100 compared to pre-industrial forcings. The four are 2.6, 4.5, 6.0 and 8.5.
The first important thing to know about RCPs comes to use directly from the IPCC. Writing in a document titled, ‘IPCC Scenario Process for AR5’ they say “The goal of working with scenarios is not to predict the future but to better understand uncertainties and alternative futures, in order to consider how robust different decisions or options may be under a wide range of possible futures”. The IPCC decided to act only as a catalyst for the process–in essence they commissioned independent scientific teams to generate the RCPs.
Maybe they used these good folks:
“As stand alone products, the RCPs have limited usefulness to other research communities. First and foremost, they were selected with the sole purpose of providing data to climate models, taking into consideration the limitations in climate models differentiating levels of radiative forcing. They lack associated socioeconomic and ecological data. They were developed using idealized assumptions about policy instruments and the timing of participation by the international community.”
They used information from the previous SRES developed for AR3 and AR4–they didn’t want to just throw numbers out there–but they did not develop the emissions narratives and economic assumptions themselves.
They are not predictions. RCP 8.5 essentially says ‘if you want to get to this level of forcing by 2100, here’s a pathway that will get you there.’ It is not the end result of a scientific look at the fuels we will burn, the emissions they will cause, the sensitivity of the atmosphere and the results of the interactions between those and other factors. It is a reasonable-sounding trajectory that will get you to that result. It is meant to feed into climate models to keep the data consistent. It is not meant to be used as a prediction to form other scientific work or policy.
The problem is that RCP 8.5 is being used as a ‘business as usual’ scenario with the force of a prediction. People are using it in scientific papers as if it were the worst case scenario with their sketchy numbers borrowed from previous work being treated as if it were the sober judgment of scientists working in 2014, as opposed to scenarios created back in 2000.
RCP 8.5 comes up with these assumptions to get them to their goal–not vice versa:
“RCP 8.5 – High emissions This RCP is consistent with a future with no policy changes to reduce emissions. It was developed by the International Institute for Applied System Analysis in Austria and is characterised by increasing greenhouse gas emissions that lead to high greenhouse gas concentrations over time. Comparable SRES scenario A1 F1 This future is consistent with: Three times today’s CO2 emissions by 2100 Rapid increase in methane emissions Increased use of croplands and grassland which is driven by an increase in population A world population of 12 billion by 2100 Lower rate of technology development Heavy reliance on fossil fuels High energy intensity No implementation of climate policies.”
Is it possible? Sure. Is it likely? I don’t know. Is it a prediction of the future?
“Therefore, there is a need to develop socioeconomic and climate impact scenarios that draw on the RCPs and associated climate change projections in the scenario process. Referencing the RCP and climate change projections has two potential benefits; they would facilitate comparison across research results in the CM, IAM, and IAV communities, and facilitate use of new climate modeling results in conjunction with IAV research.
“The parallel phase has several components. Within CMIP5, CM teams are using the RCPs as an input for model ensemble projections of future climate change. These projections will form the backbone of the IPCC’s Working Group I assessment of future climate change in the 5th Assessment Report (AR5). The IAM community has begun exploring new socioeconomic scenarios and producing so-called RCP replications that study the range of socioeconomic scenarios leading to the various RCP radiative forcing levels. In the meantime, IAV analyses based on existing emission scenarios (SRES) and climate projections (CMIP3) continue.
“In the integration phase, consistent climate and socioeconomic scenarios will inform IAM and IAV studies. For example, IAV researchers can use the new scenarios to project impacts, to explore the extent to which adaptation and mitigation could reduce projected impacts, and to estimate the costs of action and inaction. Also, mitigation researchers can use the global scenarios as “boundary conditions” to assess the cost and effectiveness of local mitigation measures, such as land-use planning in cities or changes in regional energy systems.
“These scenarios need to supply quantitative and qualitative narrative descriptions of potential socioeconomic and ecosystem reference conditions that underlie challenges to mitigation and adaptation. And they have to be flexible enough to provide a framework for comparison within which regional or local studies of adaptation and vulnerability could build their own narratives. The defining socioeconomic conditions of these scenarios have been designated Shared Socioeconomic reference Pathways (SSPs).”
Source: A framework for a new generation of socioeconomic scenarios for climate change impact, adaptation, vulnerability, and mitigation research; Arnell, Kram, Carter et.al