Saturday, January 4, 2014

What If We Burn All the Fossil Fuel Reserves? Simple Arithmetic Using the IPCC AR5

What happens if we burn all the fossil fuel reserves that we have? Here I'm doing my own simple arithmetic.

Above all, the Working Group I's contribution to the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) states that there is a specific threshold (purple line in the figure below) of total carbon emissions to us, Homo sapiens. To check the global surface temperature rise within 2°C (degrees Celsius) from the pre-industrial level, we have to limit our cumulative carbon emissions since 1870 to no more than 790 gigatonnes of carbon (GtC) or 2900 gigatonnes of CO2 (GtCO2).

(Here, I want to leave five notes. First, the Summary for Policymakers (SPM) of the WGI's AR5, originally released on September 27 last year, was corrected for errors on November 11. Second, the emissions numbers are rounded to the nearest 5 GtC (or nearest 5 GtCO2). Third, ideally, the pre-industrial level means the global surface temperature in 1750. In the case of the figure below as cited from the AR5, the pre-industrial temperature is set at the 1861-1880 average level. I think it is because the estimates for 1750-1860 period were too uncertain to be scientifically acceptable. Fourth, the famous 1000 GtC carbon budget is the sum of CO2 (790 GtC) and non-CO2 emissions (210 GtC). For the CO2 only, the cumulative emissions limit is 790 GtC. Fifth, I didn't consider the possible emissions from future land use change in this post.)

The AR5 estimated that about 515 GtC (1890 GtCO2) had been emitted from 1870 to 2011 (blue line in the figure). The number includes emissions from land use change in addition to the emissions from fossil fuel combustion and cement production. The Carbon Dioxide Information Analysis Center estimated that the global cumulative anthropogenic carbon emissions from fossil fuel combustion and cement production were about 370 GtC (1360 GtCO2) between 1870 and 2011. The remaining 145 GtC (530 GtCO2) seems to be emitted from land use change. Therefore, at the beginning of 2012, we had only 275 GtC (1010 GtCO2) of carbon at our disposal.

Then, we can now go back to the question I asked in the first line of this post. "What happens if we fully exploit the fossil fuel reserves on earth?"

To answer the question, we have to know the amount of carbon sources. We have figures for the global fossil fuel reserves that are summarized in my previous post ( The post tallied that the total combined reserves of global oil, natural gas, and coal were about 995.7 billion toe as of the year end of 2011 (= oil 224.0 billion toe + natural gas 174.3 billion toe + coal 597.4 billion toe). (Here, let us forget about 14,435 billion toe of fossil fuel resources calculated in the post. The resources estimates are 14.5 times larger than the already enormous reserves.)

In 2011, the annual global carbon emissions were 9.46 GtC (34.7 GtCO2). If we don't change our fossil fuel consumption habits, we will use up the remaining 275 GtC in only 29.1 years. If we consume the entire fossil fuel reserves, we will eventually emit approximately 930 GtC (3400 GtCO2) of additional carbon in 81 years (= reserves-to-production (R/P) ratio of the global fossil fuels in 2011) or by 2092. We will pass the threshold and go further to emit 655 GtC (2390 GtCO2) more.

This self-destructing anthropogenic emissions will follow a global emissions trajectory that is little short of the IPCC's second-fastest global warming scenario (RCP6.0; orange line in the figure). The RCP6.0's additional cumulative CO2 emissions between 2012 to 2100 are estimated 1060 GtC (3885 GtCO2), while the total additional CO2 emissions by burning up the entire fossil fuel reserves between 2012 and 2092 are 930 GtC (3400 GtCO2). It means our extravagance could result in 3°C global warming around the end of the 21st century (Rogelj et al., 2012).

So.... We really are in a grave danger. I want to find a solution for this situation, not from another arithmetic but from profound reasonings that can move selfish people's hearts. (When do I? Not sure....)

Figure source: IPCC WGI (2013)

Emission factors (source: IPCC WGIII (2007)):
Coal:3,851,856 gCO2/toe(originally, 92.0 gCO2/MJ)
Gas:2,193,883 gCO2/toe(originally, 52.4 gCO2/MJ)
Oil:3,194,528 gCO2/toe(originally, 76.3 gCO2/MJ)


Carbon Dioxide Information Analysis Center (CDIAC). (2013). Fossil-Fuel CO2 Emissions. Oak Ridge, TN: Oak Ridge National Laboratory. [Data at]

Rogelj, J., Meinshausen, M., & Knutti, R. (2012). Global warming under old and new scenarios using IPCC climate sensitivity range estimates. Nature Climate Change, 2(4), 248-253. [Full-text at]

Working Group I. (2013). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Bern, Switzerland: IPCC Working Group I. [Full-text at]

Working Group III. (2007). Climate Change 2007: Mitigation of Climate Change. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK and New York, NY: Cambridge University Press. [Full-text at]

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