Guest post by David Middleton
Featured image borrowed from here.
In light of the fact that I totally glossed over the distinction between “CO2” and “CO2 equivalent” in my previous post on RCP 8.5, I decided to pen a more serious post on the subject. I will do my best to avoid humor.
In most, if not all, catastrophic AGW papers, RCP 8.5 (or an equivalent) is invoked as a “business as usual scenario.” A recent example can be found here. The peer-reviewed paper said, “Antarctica has the potential to contribute more than a metre of sea-level rise by 2100.” This was translated by journalists into, “Antarctic ice sheets are expected to double sea-level rise to two metres by 2100, if carbon emissions are not cut.”
There is a world of difference between “has the potential to” and “are expected to,” particularly when the “potential” is based on an insanely unrealistic scenario.
The Stuff Nightmares Are Made From
Dr. Judith Curry has a very thoughtful discussion of RCP 8.5, “the stuff nightmares are made from,” on her Climate Etc. blog…
(1) AN INTRODUCTION TO SCENARIOS ABOUT OUR FUTURE
In AR5 four Representative Concentration Pathways (RCPs) describe scenarios for future emissions, concentrations, and land-use, ending with radiative forcing levels of 2.6, 4.5, 6.0, and 8.5 W/m2 by 2100. Strong mitigation policies result in a low forcing level (RCP2.6). Two medium stabilization scenarios lead to intermediate outcomes: (RCP4.5, RCP6.0).
RCP8.5 gets the most attention. It assumes the fastest population growth (a doubling of Earth’s population to 12 billion), the lowest rate of technology development, slow GDP growth, a massive increase in world poverty, plus high energy use and emissions. For more about the RCPs see “The representative concentration pathways: an overview” by Detlef P. van Vuuren et al, Climatic Change, Nov 2011.
RCP8.5 assumes a nightmarish world even before climate impacts, resulting from substantial changes to long-standing trends. It provides AR5 with an essential worst case scenario necessary for conservative planning.
Unfortunately scientists often inaccurately describe RCP8.5 as the baseline scenario — a future without policy action: “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, This is a material misrepresentation of RCP8.5. Scientists then use RCP8.5 to construct horrific visions of the future. They seldom mention its unlikely assumptions.
“Scientists then use RCP8.5 to construct horrific visions of the future.” Why would “scientists” feel compelled “to construct horrific visions of the future”? Furthermore, why would they so often describe these “horrific visions of the future” as baseline, expected or “business as usual” scenarios?
Testing RCP 8.5
One of the commenters to my previous post was kind enough to direct me to the RCP database. Using the RCP data and BP’s Statistical Review of World Energy 2015, I will demonstrate the absurdity of RCP 8.5 in a more “apples to apples” manner than my previous post. I will compare the carbon emissions and atmospheric CO2 concentrations depicted in RCP 4.5, 6.0 and 8.5 to real world data.
From my previous post:
Using BP’s Statistical Review of World Energy 2015, I built a “model.”
This “model” derives two equations:
- CO2 (ppm) = 0.0002*(MTOE) + 320.87 (R² = 0.9986)
- MTOE = 142.16*(Year) – 275,639 (R² = 0.9698)
Note: MTOE = Millions of Tonnes of Oil Equivalent.
Note to nitpickers: Yes, I know the top and bottom charts and equations 1 and 2 should have been listed in the opposite order.
These two equations enable me to project fossil fuel use and atmospheric CO2 into the distant future (beyond my retirement date… which with oil at $30/bbl is either very far off in the future or sooner than I would prefer). Using the assumption that the mix of crude oil, natural gas and coal would remain at a constant ratio (that of the period 2005-2014), I come up with an atmospheric CO2 concentration of 683 ppm in 2100, about half of RCP 8.5 (Venus) and comparable to RCP 4.5 (non-catastrophic).
To better reflect reality, I looked more closely at the evolution of the ratio of crude oil, natural gas and coal in the fossil fuels mix and I noticed that natural gas and crude oil exhibit very robust trends…
Combining my previous method of projecting total fossil fuel use and the trends in Figure 3, I came up with this…
No doubt Peak Oilers will welcome the return of Peak Oil some time around 2060.
Using BP’s numbers for carbon dioxide emissions…
oil – 73,300 kg CO2 per TJ (3.07 tonnes per tonne of oil equivalent)
natural gas – 56,100 kg CO2 per TJ (2.35 tonnes per tonne of oil equivalent)
coal – 94,600 kg CO2 per TJ (3.96 tonnes per tonne of oil equivalent)
I built carbon emissions scenarios for two cases:
- Constant ratio of oil, gas & coal based on 2005-2014 averages (left).
- Decreasing oil, increasing gas and relatively stable coal, based on trends in Figure 3 (right).
Based on a real world “business as usual” emissions scenario, with natural gas displacing oil at its current pace and no carbon tax, I come up with a CO2 right about inline with RCP 6.0, “a mitigation scenario, meaning it includes explicit steps to combat greenhouse gas emissions (in this case, through a carbon tax)“.
Then I took my real world “business as usual” relative concentration pathway and applied three reasonable climate sensitivities to it: 0.5, 1.5 and 2.5 °C per doubling of atmospheric CO2, starting at 280 ppmv (TCR 0.5, TCR 1.5 and TCR 2.5). HadCRUT4, referenced to 1850-1879 is clearly tracking very close to TCR 1.5…
Since it is generally assumed that at least half of the warming since 1850 was natural, the actual climate sensitivity would have to be significantly lower than 1.5 °C per doubling. Therefore, RCP 8.5 should never be described as “business as usual,” “expected” or a “baseline case.” Since its assumptions are mind mindbogglingly unrealistic, it shouldn’t be used in any serious publication. It is bad science fiction.