This really is just about the worst post ever. I’m leaving it up as I hope to update it with better information. Read on at your own risk…
Picking up where we left off yesterday, Judith Curry thinks we should take the ‘plausible worst case scenario’ on which to base our plans for living with climate change in the 21st century.
The IPCC has a case that they are putting forward as just such a worst case scenario. It is called RCP 8.5. It is based on what the IPCC says are ‘internally consistent set of economic assumptions’ and is one of four such scenarios. RCP 8.5 is the most pessimistic.
RCP stands for ‘Representative Concentration Pathway’. It attempts to chart the increase in forcings on our atmosphere, measured in watts per square meter. Most of the assumptions are adopted wholesale from the scenarios that RCP replaced–the SREs used in prior versions of IPCC reports AR3 and AR4 .
RCP 8.5’s answers to the important question are, emissions will more than triple during this century, radiative forcing will quadruple and temperatures will rise 4.9C over the pre-industrial period.
To evaluate its fitness for purpose we need to examine the assumptions involved. We should be aware of the worst case scenario, but it has to be plausible.
These assumptions don’t appear to be in any one place, either by the term RCP 8.5, SRES A1F1 or SRES Ar2. If anyone can help me find them I will be forever in your debt.
At Climate Change National Forum, John Nielsen-Gammon describes RCP 8.5: “RCP8.5 was developed to represent a high-end emissions scenario. “Compared to the scenario literature RCP8.5 depicts thus a relatively conservative business as usual case with low income, high population and high energy demand due to only modest improvements in energy intensity.” (Riahi et al. 2011) RCP8.5 comes in around the 90th percentile of published business-as-usual (or equivalently, baseline) scenarios, so it is higher than most business-as-usual scenarios. (van Vuuren et al. 2011a).”
Here are the assumptions underlying RCP 8.5:
Population: They assume population will reach 12 billion by 2100. This is well above the UN median projection of 10.1 billion, but less than their high variation of 15.8 billion.
Urbanization: SRES A2r assumes 85% urbanization by 2100
Emissions: RCP 8.5 assumes peak emissions in 2090 at 27.5 PgC (petagrams of carbon)
Concentrations: RCP 8.5 assumes CO2 concentrations reaching 950 ppm by 2100, more than double current concentrations of 400 ppm.
GDP: Skeptical Science has a chart saying that RCP 8.5 shows global GDP growth to a little less than $200 trillion in US 2000 dollars, which is bizarre, because everybody else shows results in 2005 US dollars. I can’t trust them, but it’s really hard to find these figures. (Help!) The US DOE Energy Information Administration predicts global GDP to reach $200 trillion by 2040…
Energy Consumption: It appears that RCP 8.5 projects energy consumption to reach 1,657 quads by 2100. In 2010 the globe consumed 523 quads. Sadly, I think they have underestimated consumption–as faithful readers know, my projection for energy consumption at my other blog serves as its title–I project consumption to reach 3000 quads by 2075, before stabilizing.
Okay, I don’t even know if I should publish this post. In population, RCP 8.5 looks mid-range, if somewhat pessimistic. They really think GDP is going to grow slowly. But energy consumption? That looks low.
I confess I need help with this. If help arrives I will update this. Quickly, as it is a bit of an embarrassment.
Ah, well–work in progress.