Fossil Fuels

One of the strangest anthropogenic global warming denialist arguments is that there may not be enough fossil fuels (coal, oil and natural gas) to cause the worst case scenarios described in the IPCC report [1].  It is strange for two reasons.  The first is that unlike other denialist objections, there is actually credible scientific support for this argument.  The second reason is that the policy solutions to problems caused by either global warming or running out of fossil fuels are the same: effecting a rapid transition to alternative sources of energy and conservation. 

 One of the most important figures in the resource depletion discussion is Kjell Aleklett, founder of the Association for the Study of Peak Oil [2].  Aleklett has done as much as anybody to investigate the actual reserves of fossil fuels and inform the public about this possible crises.  Curiously, Senator Inhofe quotes Aleklett [3]:   “the combined volumes of these fuels are insufficient to cause the changes in climate….The world’s greatest future problem is that too many people must share too little energy.”  If Inhofe’s objection to anthropogenic climate change theory were purely academic then citing Aleklett may support that position, but given his objection to the theory is policy-based, i.e., opposition to government support for a transition away from fossil fuels, his reference to resource depletion arguments clearly undermines his position.

I have previously described the impact of even the lowest credible estimates of fossil fuel resources on global warming and shared this information with Supervisor Lori Waters in December, 2008.  The document I gave to Waters is publicly available on the Sustainable Loudoun webs site [4].

 Aleklett’s view is articulated in several of his papers (see for example [5]).  While I have great respect for Aleklett and agree in general with his pessimism regards remaining and depleting resources, I disagree with him that the impact of even the lowest estimates may not initiate a serious climate problem.  Further, while I believe that when we are evaluating our potential energy problems, we need to consider the most pessimistic resource estimates in order to understand the worst case scenario, when we are evaluating potential global warming problems, we need to consider a wide range of resource estimates including the most credible optimistic estimates in order to evaluate the worst case scenarios.  Therefore, I submit that while his criticism of the IPCC may have substantial scientific support, it is not a reasonable objection because there is not one hundred percent certainty in the most pessimistic resource depletion scenario.  The impact on policy is the same in either case.  Aleklett as an academic may be correct to criticize the IPCC for not including an additional low resource scenario.  Inhofe a fossil-fuel industry sponsored politician is foolish to think that argument overturns the need for more enlightened policy.

The lowest estimate for remaining fossil fuels as measured by total carbon content is about 560 Gigatons Carbon (GtC) from Rutledge [6].  The highest credible estimate is about 5000 GtC from Rogner [7].  These represent total estimated recoverable resources and reserves of fossil fuels.  The most disquieting aspect of these estimates is that we don’t have any idea how much fossil fuels was have left to within an order of magnitude.  That is the most compelling argument against Inhofe’s objection to conservation and transitioning to alternative energy sources as quickly as we possibly can. 

 In reference [5], Aleklett presents estimates for remaining fossil fuels which may be used before 2100, assumed by the IPCC, in barrels of oil equivalent.  We can convert these numbers to GtC using the conversion factors described below.  Thus the IPCC report [1] analyzes several scenarios with a range of carbon emissions between 1243 to 1960 GtC during the 21st century.  We observe that these estimates are far below Rogner’s high estimate (5000) but higher than the estimate of Rutledge (560).  The IPCC did not use either the most pessimistic or optimistic estimates for remaining recoverable fossil fuels but instead tacked responsibly up the middle.

 The best case scenario for the climate and the worst case scenario for fossil fuel depletion is Rutledge’s estimate of 560 GtC.  While it is frightening to speculate on the impact to our economy if politicians like Inhofe prevail in preventing us from developing a transition plan to alternative renewable energy sources in time, it is also sobering to speculate on the human impact on climate even in this scenario.  Working in our favor (for the climate and not life in the oceans, unfortunately) is the fact that land and ocean sinks currently absorb about 50% of our emissions, though there is evidence that these sources are becoming saturated [8].  Increasing temperatures and acidity may reduce ocean productivity and this would reduce the amount of our CO2 emissions which can be absorbed by the oceans.  Thus 560 GtC may increase atmospheric carbon by as much as 134 ppmV depending on how quickly it is extracted and consumed (divide 560 GtC by 2.1 to convert to ppmV and then by 2 since 50% is absorbed by the oceans and land sinks).  However, the carbon stock in the Earth’s forests (above ground) is 288 GtC [9].  This can increase atmospheric carbon by another 69 ppmV if it is burned.  Imagine a world inhabited by up to 9 billion humans who have no fossil fuels left to keep themselves warm.  Whatever does not get harvested may be destroyed by insects and fire.  It is not hard to imagine all forests disappearing as this level of devastation has been caused by human societies locally in the past, e.g. Easter Island and Yucatan [10](Diamond, 2005). 

Further, if CO2 levels remain above 350 ppmV for an extended period of time, permafrost may melt releasing carbon in the form of carbon dioxide and/or methane into the atmosphere as a consequence of increased warming of the climate.  The permafrost is estimated to contain up to 1500 GtC [11, 12].  Other positive carbon cycle feedbacks have been identified but are not discussed here.  The amount of permafrost melt is a function of both the temperature and thus the level of atmospheric carbon, and the length of time the temperature remains elevated.  Higher levels of CO2 means the Earth warms to a higher temperature resulting in a faster melting of the permafrost. 

 The best case climate scenario and the worst case energy scenario assume human emissions of 560 GtC which adds 134 ppmV CO2 to the atmosphere.  This brings the total to 525 ppmV.  The consumption of the planet’s forests adds 69 ppmV bringing the total to 594 ppmV.  This level of CO2 would accelerate the melting of the permafrost and other carbon cycle feedbacks.  Eventually (over centuries) all 1500 might be emitted into the atmosphere bringing the total to 950 ppmV.  An MIT report [13] projects 10 degrees F global warming and 20 degrees F warming in the arctic if the CO2 concentration reaches 866 ppmV. At these temperatures sub-ocean methane hydrate deposits may thaw adding additional carbon in the form of methane or carbon dioxide to the oceans (accelerating ocean acidification) and the atmosphere [14, 15].  The MIT study authors assume we reach 866 ppmV via human emissions but it doesn’t matter where the CO2 comes from.  Current climate models do not account for melting permafrost sources.

 Another important observation (and cautionary note) is that most model projections continue only up to 2100 as if our destruction of the ecosystem, upon which we depend, stops at that time.  It does not.  In another article, Pliocene [16] we observed that between 5 and 2 million years ago, the level of carbon in the atmosphere was the same or a little less than it already is today yet temperatures were between 2 and 4 degrees Centigrade warmer.  It is suggested that this may be because the Earth was cooling off as it was losing atmospheric carbon dioxide and the oceans had already equilibrated to a higher temperature and had to cool down.  Today we are recovering from the Last Glacial Maximum (LGM) some 20,000 years ago and oceans are cooler and have to warm before the surface does.  Most of the energy imbalance in fact is warming the oceans today rather than the atmosphere or the surface.  This will continue for a long time and our problems are only just beginning ninety years from now.

In conclusion, it is possible that even the most pessimistic estimates for fossil fuel resources are enough to cause disastrous global warming especially if positive carbon cycle feedbacks kick in.  Human society will be trying to adapt to increasingly unlivable conditions without the benefit of fossil fuel energy.

 Tony Noerpel

—————————————A note on conversion of units————————————————–

 Strictly speaking barrels of oil equivalent is a relative measure of the energy content of these three fuel types, coal, oil and natural gas, and not exactly proportional in their carbon emissions.  But this is the case even if we consider only coal, since, for example, the quality of anthracite is superior to the quality of lignite in terms of energy available per quantity of carbon emissions.  Following Aleklett we use 42 Giga Joules (GJ) as the energy content of a ton of oil equivalent and 6.12 GJ as the energy content of a barrel of oil equivalent and assume most of the mass of a ton of fossil fuels is carbon.  This is accurate enough for a first order estimate and anyway we are only interested in bounding a problem which has an order of magnitude uncertainty to begin with.  One important caveat is that remaining fossil fuels include a high proportion of dirty fuels such as heavy oils, lignite, kerogen and bitumen which all have higher carbon content per useable British Thermal Unit (BTU) when compared to the light sweet crude oil and anthracite coal we have been using.  Remaining resources require more energy inputs for the same energy output.  For example, the United States coal production as measured in tons has continued to increase but as measured by BTU, or energy content, has actually peaked in 1998 [17].  This is because the quality of remaining coal reserves is diminishing.  Most of the high quality Anthracite has been mined and the remaining resources include sub-bituminous coal and lignite.  

 The conversion of GtC to parts per million by volume (ppmV) of atmospheric carbon is straightforward.   We need to compute the average molecular weight of the molecules in the atmosphere.  The components are 78.08% Nitrogen with a molecular mass of 28, 20.9% Oxygen with a molecular mass of 32 and 0.9% Argon with a molecular mass of 40.  Thus .7808 X 28 + .209 X 32 + 0.009 X 40 = 28.9.  Carbon Dioxide has a molecular weight of 44 but the Carbon content of a CO2 molecule has a mass of 12.  The mass of the Earth’s atmosphere is 5.15 106 Gt.  Thus divide GtC by the factor 5.15 X 12/28.9 = 2.1 to compute ppmV.  The current level of atmospheric CO2 is 392 ppmV [18] which can then be converted to 823 GtC by multiplying by 2.1.


[1] Intergovernmental Panel on Climate Change, 2007,

[2] ASPO web site

[3] Inhofe, Morano, and Dempsey, December 20, 2007, “U. S. Senate Report Over 400 Prominent Scientists Disputed Man-Made Global Warming Claims in 2007 Scientists Debunk ‘Consensus’”.

 [4] sustainable Loudoun web site

 [5] Kook, M., Sivertsson, A., Aleklett, K., “Validity of the fossil fuel production outlooks in the IPCC Emission scenarios, Natural Resources Research, Volume 19, Issue 2, June 2010, 63-81, doi:10.1007/s11053-010-9113-1.

 [6] Rutledge, D., 2007, presentation and excel worksheet can be downloaded here.

Rutledge, D. Hubbert’s peak, the coal question and climate change, APSO-USA World Oil Conference, 17-20 October 2007, Houston, Texas.

 [7] Rogner, H. H., An assessment of world hydrocarbon resources, Annual Review of Energy and the Environment, 22:217-262, 1997.

 [8] Canadell, J. G. et al. 2007 Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks.” Proc. Natl. Acad. Sci. USA 104, 18-866-18 870.

 [9] Moutinho, P. and Schwatzman, S. (eds) Tropical deforestation and climate change, Belem, Brazil: Amazon Inst. For Environmental Research.

 [10] Diamond, J., 2005 Collapse, Penguin Books, London.

 [11] Tarnocai, C., Canadell, P.,  Journal of Global Biogeochemical Cycles (GB2023,doi:10.1029/2008GB003327) American Geophysical Union.

 [12] Edward A. G. Schuur, Jason G. Vogel, Kathryn G. Crummer, Hanna Lee, James O. Sickman, T. E. Osterkamp,  “The effect of permafrost thaw on old carbon release and net carbon exchange from tundra,” Nature 459, 556-559 (28 May 2009) doi:10.1038/nature08031 Letter

 [13] MIT: , Report 169,, Probabilistic Forecast for 21st Century Climate Based on Uncertainties in Emissions (without Policy) and Climate Parameters by Sokolov, A.P., P.H. Stone, C.E. Forest, R.G. Prinn, M.C. Sarofim, M. Webster, S. Paltsev, C.A. Schlosser, D. Kicklighter, S. Dutkiewicz, J. Reilly, C. Wang, B. Felzer, J. Melillo, H.D. Jacoby (January 2009) Joint Program Report Series, 44 pages, 2009, also Journal of Climate October 2009, Vol. 22, No. 19 : pp. 5175-5204

 [14] Additional information on these carbon cycle feedbacks:, and, and

 [15] Shakhova, N., Igor Semiletov, I., Salyuk, A., Yusupov, V., Kosmach,D., Gustafsso, O., Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf, Science 5 March 2010: Vol. 327. no. 5970, pp. 1246 – 1250 DOI: 10.1126/science.1182221

 [15] brleader Pliocene

 [16] Lehmann, H., et al 2007 Coal resources and future production, Energy Watch Group publication 1/2007


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