Misrepresentation of business-as-usual emissions: The red herring of RCP8.5

The notorious Breakthrough Institute has been busy. Their director of climate and energy has been allowed by the editors of Nature to publish a critique of the use of RCP8.5 as BAU.* While it is true that many papers misinterpret RCP8.5 as being the worst case scenario and that this is equivalent to BAU, the authors of the RCPs recently reminded the climate community that RCP8.5 assumed maximum burning of coal , which is not what is happening and not likely to occur.  

We have been aware of the misuse of RCP8.5 for quite a while, but the purpose of the commentary in Nature was to make the claim that BAU will lead to about 3.0˚C global average warming by the end of the century. Of course, this level of climate change would be nothing short of catastrophic and the scientific community is nowhere near reaching a consensus that this is would be the outcome of BAU. Moreover, the latest estimates of Equilibrium Climate Sensitivity suggest that we are on track to warm as much as 6˚C. To be sure, this result is being questioned by leading climate scientists such as Gavin Schmidt. Stay tuned to see what happens as the various modeling groups work out their differences and validate the models. 

The problem with dismissing RCP8.5 is that one interpretation of the trajectory of warming indicates that we may be on this path or slightly higher. If so, what is the source of the additional climate forcing? This morning Michael Mann produced his review of the Nature article and notes that the spin in this commentary is not supported by the science. Mann points out the difficulty in assessing the track we are on, and more importantly, he emphasizes that we know almost nothing about positive feedbacks from the biosphere. Certainly these feedbacks are poorly constrained in projections, likely very large, and rapidly growing.

One good thing about the article in Nature is that it provides a brief explanation of the improvements in the scenario analysis that will be presented in the AR6. Under development is a subset of the SSP models (Shared Socioeconomic Pathways) that will function in a similar way to the RCP scenarios in the AR5.  Although this represents a conceptual improvement, the new scenarios promise to be very complex. The big unknown in all of this is what humanity will do. Our economy will be the driver of whatever path we assume moving forward. 

About the Breakthrough Institute

This organization got its start with an article entitle The Death of Environmentalism. The authors, Michael Shellenberger and Ted Nordhaus have since become the darlings of the business elite and they are featured regularly in the Wall Street Journal. Neither Shellenberger or Nordhaus has a terminal degree in any science, but they have apparent collaborations with conservative think tanks and conservative leaning scientists, such  as David Kieth at Harvard who is a leading advocate of geoengineering and has financial connections to corporate development of this technology. Nordhaus is the nephew of William Nordhaus, who won the Nobel in Economics for his development of an economic model for assessing the impact of climate change (Many of us regard this model as worthy of scorn, rather than a Nobel).

The Breakthrough Institute has no academic or scientific staff to speak of, yet they seem to have an outsized credibility in the press.  One of their recent “breakthroughs” is a white paper known as The Ecomodernist Manifesto. The most glaring flaw in their argument that we can have a “good” Anthropocene is that they ignore ecosystems and biosphere responses to environmental degradation and climate change. There is no mention whatever of the massive management efforts that would be required to realize this vision. 

Perhaps most worrisome about the Breakthrough Institute is their insistence that we should burn fossil fuels generously as we develop other sources of energy. Their rationale for this is that energy-dense fuels such as coal and nuclear will result in less climate damage than the rapid development of renewables. Although there is some logic in this, their argument about energy-rich fuels should not preclude the development of renewables. Moreover, they ignore the social costs of further development of fossil fuels. Needless to say, the fossil fuel industry loves the Breakthrough Institute. 

So what is the bottomline about RCP8.5? Depending on what the data show, it may be a useful surrogate for BAU, although this was not its intended purpose.  We need to see what the data reveal moving forward. There is no doubt that the big unknown is biosphere feedback


  • RCP = Relative Concentration Pathway; Developed to describe possible emissions scenarios in the IPCC Fifth Assessment Report (AR5). BAU = Business as Usual.