BOE: Upper Limits on Fossil Fuel Contribution to Atm CO2
This post is a back of the envelope calculation to answer: “How much would CO2 increase if we burned all the available fossil fuels.” It does not consider feedbacks. It considers two scenarios: Proven and Optimistic
Proven reserve estimates are gleened off wiki. Proven is a subset of discovered and refers to only those reserves which can be developed with current technology and under current economic conditions. My estimate is that there are 2,200 gigatonnes of CO2 in proven reserves which is in the same ballpark as the approx 2,800 gigatonnes estimated in Meinhausen 2009. This will result in an approximate increase of 274 ppm. To which I add the approx 100 ppm already produced in the industrial era for a net increase of 374 ppm.
Given an increase in CO2 (dCO2) sourced from fossil fuels, we can calculate the change in Radiative Forcing: dRF = 5.35 * ln( (280+dCO2)/280 ).
Likewise, we can calculate lambda λ as the Equilibrium Climate Sensitivities (ECS) divided by the radiative forcing of doubled CO2: λ = ECS/3.7
Given those two values, an estimate of the change of Temperature due to fossil fuel CO2 forcing is trivial to calculate: dT = λ * dRF
Using a spread of possible ECS [2,3,4.5,7], we can estimate that previous fossil fuel consumption and the future consumption of all proven reserves of fossil fuels will result in a warming of 2.5-5.5C for ECS of 2-4.5C and a warming of 8.6C for an ECS of 7C.
I include ECS = 7, due to our recent discussion of Sherwood and Hubert 2010 which claims that Meinhausen 2009 estimates that there is a 5% possibility of an ECS exceeding 7.1C. As an aside, I think this claim may be a misunderstanding based on the following Meinhausen quote: We chose a Bayesian approach, but also obtain ‘frequentist’ confidence intervals for climate sensitivity (68% interval, 2.3–4.5C; 90%, 2.1–7.1C), which is in approximate agreement with the recent AR4 estimates.. If the 90% interval had an even split of 5% on either tail, you could claim 5% chance that ECS > 7.1C. But examining Fig 3 indicates that almost the entire remaining 10% lies on the cool side of the 90% range, not evenly split between the two. It is likely that given distribution shows an ECS > 7.1C probability of less than 1%.
Wiki also includes an inflated “Optimistic” resource scenario is not optimistic from an AGW point of view, but “optimistic” from a resource availability point of view. While I found these estimates on wiki, they are attributed to “Oil & Gas Journal, World Oil.” I haven’t found the original source and none of the internet cites seem to include a date.
In general, “proven reserves” in the oil industry refers to resources that will probably (~90%) be developed with known technology under current economic conditions. It is possible that the “optimistic” numbers come from “proven, probable, possible” reserves aka 3P.
One issue that arises in forecasting production is that as technology increases and/or prices rises, resources that were previously would have been unprofitable to develop, become potentially profitable and the resource previously “unproven” move to “proven.”
Assuming 1) the ‘optimistic’ numbers are discovered resources but unproven and 2) that rising prices don’t destroy demand and 3) resource extraction technology continues to improve, then it seems quite possible that most of the discovered resources will eventually become proven and produced. In that case, as modeled on the table shown below, atmospheric CO2 will increase by 646 ppm (~5200 Gt), more than double the previous estimate. Cell H5 shows that future production plus 100 ppm for previous production.
Uncertainty in ultimate recoverable resources (URR) is not the only uncertainty even in this rough estimate. Currently, the oceans absorb approximately 50% of our fossil fuel CO2 emissions. This number is expected to decrease over time, but I’m not sure how far or how fast. I’ll guestimate that maybe 30% of our future emissions will be absorbed. On the other hand, I don’t think these reserve estimates include fuels potentially derived from oil sands (bitumen) or oil shales (kerogen). It’s possible that there could be as much potential oil in those sources as there is conventional oil, maybe more. Lets add a potential 30% upside to account for these resources. So to cover the spread, lets map the two scenarios – Optimistic and Proven – with 30% greater and 30% fewer emissions. As charted below:
Last word on the BOE. By design, there are two potentially large sources of GHG not included in this fossil fuel estimate. One is the potential exploitation of methyl hydrates as a fuel source. Another is the potential release of methane from permafrost and ocean sources as the planet warms.
As discussed earlier, my rule of thumb for now is that catastrophe lies somewhere around warming > 6C and/or atm CO2 > 1000ppm. If all available fossil fuels are burned, we might be screwed through acidification. If ECS is indeed > 7.1C, we are screwed due to warming. Even at ECS ~ 4.5C, we have crossed out of my “safe zone” if we burn all the fossil fuels at our disposal. If ECS is 3C or less and we avoid burning everything, we have a better safety margin. The potential existential threat appears to lie closer to the realm of possibility than I realized and am moved toward a more cautionary position.
Below is the IPCC AR4 WG1 Technical Summary Table 5 which shows a range of expected warming for different concentrations of CO2. Add 280 ppm to the figures displayed above to get total CO2 in the two scenarios.
Spreadsheet should be available here