In a paper recently published in the international peer-reviewed journal Energy & Fuels, Dr. Robert H. Essenhigh (2009), Professor of Energy Conversion at The Ohio State University, addresses the residence time (RT) of anthropogenic CO2 in the air. He finds that the RT for bulk atmospheric CO2, the molecule 12CO2, is ~5 years, in good agreement with other cited sources (Segalstad, 1998), while the RT for the trace molecule 14CO2 is ~16 years. Both of these residence times are much shorter than what is claimed by the IPCC. The rising concentration of atmospheric CO2 in the last century is not consistent with supply from anthropogenic sources. Such anthropogenic sources account for less than 5% of the present atmosphere, compared to the major input/output from natural sources (~95%). Hence, anthropogenic CO2 is too small to be a significant or relevant factor in the global warming process, particularly when comparing with the far more potent greenhouse gas water vapor. The rising atmospheric CO2 is the outcome of rising temperature rather than vice versa. Correspondingly, Dr. Essenhigh concludes that the politically driven target of capture and sequestration of carbon from combustion sources would be a major and pointless waste of physical and financial resources.

Essenhigh (2009) points out that the IPCC (Intergovernmental Panel on Climate Change) in their first report (Houghton et al., 1990) gives an atmospheric CO2 residence time (lifetime) of 50-200 years [as a "rough estimate"]. This estimate is confusingly given as an adjustment time for a scenario with a given anthropogenic CO2 input, and ignores natural (sea and vegetation) CO2 flux rates. Such estimates are analytically invalid; and they are in conflict with the more correct explanation given elsewhere in the same IPCC report: "This means that on average it takes only a few years before a CO2 molecule in the atmosphere is taken up by plants or dissolved in the ocean".

Some 99% of the atmospheric CO2 molecules are 12CO2 molecules containing the stable isotope 12C (Segalstad, 1982). To calculate the RT of the bulk atmospheric CO2 molecule 12CO2, Essenhigh (2009) uses the IPCC data of 1990 with a total mass of carbon of 750 gigatons in the atmospheric CO2 and a natural input/output exchange rate of 150 gigatons of carbon per year (Houghton et al., 1990). The characteristic decay time (denoted by the Greek letter tau) is simply the former value divided by the latter value: 750 / 150 = 5 years. This is a similar value to the ~5 years found from 13C/12C carbon isotope mass balance calculations of measured atmospheric CO2 13C/12C carbon isotope data by Segalstad (1992); the ~5 years obtained from CO2 solubility data by Murray (1992); and the ~5 years derived from CO2 chemical kinetic data by Stumm & Morgan (1970).

Revelle & Suess (1957) calculated from data for the trace atmospheric molecule 14CO2, containing the radioactive isotope14C, that the amount of atmospheric "CO2 derived from industrial fuel combustion" would be only 1.2% for an atmospheric CO2 lifetime of 5 years, and 1.73% for a CO2 lifetime of 7 years (Segalstad, 1998). Essenhigh (2009) reviews measurements of 14C from 1963 up to 1995, and finds that the RT of atmospheric 14CO2 is ~16 (16.3) years. He also uses the 14C data to find that the time value (exchange time) for variation of the concentration difference between the northern and southern hemispheres is ~2 (2.2) years for atmospheric 14CO2. This result compares well with the observed hemispheric transport of volcanic debris leading to "the year without a summer" in 1816 in the northern hemisphere after the 1815 Tambora volcano cataclysmic eruption in Indonesia in 1815.

Sundquist (1985) compiled a large number of measured RTs of CO2 found by different methods. The list, containing RTs for both 12CO2 and 14CO2, was expanded by Segalstad (1998), showing a total range for all reported RTs from 1 to 15 years, with most RT values ranging from 5 to 15 years. Essenhigh (2009) emphasizes that this list of measured values of RT compares well with his calculated RT of 5 years (atmospheric bulk 12CO2) and ~16 years (atmospheric trace 14CO2). Furthermore he points out that the annual oscillations in the measured atmospheric CO2 levels would be impossible without a short atmospheric residence time for the CO2 molecules.

Essenhigh (2009) suggests that the difference in atmospheric CO2 residence times between the gaseous molecules 12CO2 and 14CO2 may be due to differences in the kinetic absorption and/or dissolution rates of the two different gas molecules.

With such short residence times for atmospheric CO2, Essenhigh (2009) correctly points out that it is impossible for the anthropogenic combustion supply of CO2 to cause the given rise in atmospheric CO2. Consequently, a rising atmospheric CO2 concentration must be natural. This conclusion accords with measurements of 13C/12C carbon isotopes in atmospheric CO2, which show a maximum of 4% anthropogenic CO2 in the atmosphere (including any biogenic CO2), with 96% of the atmospheric CO2 being isotopically indistinguishable from "natural" inorganic CO2 exchanged with and degassed from the ocean, and degassed from volcanoes and the Earth's interior (Segalstad, 1992).

Essenhigh (2009) discusses alternative ways of expressing residence time, like fill time, decay time, e-fold time, turnover time, lifetime, and so on, and whether the Earth system carbon cycle is in dynamic equilibrium or non-equilibrium status. He concludes (like Segalstad, 1998) that the residence time is a robust parameter independent of the status of equilibrium, and that alternative expressions of the residence time give corresponding values.

It is important to compare Essenhigh's (2009) results with a recently published paper in PNAS by Solomon et al. (2009), the first author of which (Susan Solomon) co-chairs the IPCC Working Group One, the part of the IPCC that deals with physical climate science. This paper was published after Essenhigh had submitted his manuscript to Energy & Fuels.

The message of Solomon et al. (2009) is that there is an irreversible climate change due to the assimilation of CO2 in the atmosphere, solely due to anthropogenic CO2 emissions. From quantified scenarios of anthropogenic increases in atmospheric CO2, their implication is that the CO2 level flattens out asymptotically towards infinity, giving a residence time of more than 1000 years (without offering a definition or discussion of residence time or isotopic differences): "a quasi-equilibrium amount of CO2 is expected to be retained in the atmosphere by the end of the millennium that is surprisingly large: typically ~40% of the peak concentration enhancement over preindustrial values (~280 ppmv)". The authors' Fig. 1, i.a. shows a peak level at 1200 ppmv atmospheric CO2 in the year 2100, levelling off to an almost steady level of ~800 ppmv in the year 3000. It is not known how their 40% estimate was derived.

Solomon et al. (2009) go on to say that "this can be easily understood on the basis of the observed instantaneous airborne fraction (AFpeak) of ~50% of anthropogenic carbon emissions retained during their build-up in the atmosphere, together with well-established ocean chemistry and physics that require ~20% of the emitted carbon to remain in the atmosphere on thousand-year timescales [quasi-equilibrium airborne fraction (AFequil), determined largely by the Revelle factor governing the long-term partitioning of carbon between the ocean and atmosphere/biosphere system]".

Solomon et al. (2009) have obviously not seriously considered the paper by Segalstad (1998), who addresses the 50% "missing sink" error of the IPCC and shows that the Revelle evasion "buffer" factor is ideologically defined from an assumed model (atmospheric anthropogenic CO2 increase) and an assumed pre-industrial value for the CO2 level, in conflict with the chemical Henry's Law governing the fast ~1:50 equilibrium partitioning of CO2 between gas (air) and fluid (ocean) at the Earth's average surface temperature. This CO2 partitioning factor is strongly dependent on temperature because of the temperature-dependent retrograde aqueous solubility of CO2, which facilitates fast degassing of dissolved CO2 from a heated fluid phase (ocean), similar to what we experience from a heated carbonated drink.

Consequently, the IPCC's and Solomon et al.'s (2009) non-realistic carbon cycle modelling and misconception of the way the geochemistry of CO2 works simply defy reality, and would make it impossible for breweries to make the carbonated beer or soda "pop" that many of us enjoy (Segalstad, 1998).

So why is the correct estimate of the atmospheric residence time of CO2 so important? The IPCC has constructed an artificial model where they claim that the natural CO2 input/output is in static balance, and that all CO2 additions from anthropogenic carbon combustion being added to the atmospheric pool will stay there almost indefinitely. This means that with an anthropogenic atmospheric CO2 residence time of 50 - 200 years (Houghton, 1990) or near infinite (Solomon et al., 2009), there is still a 50% error (nicknamed the "missing sink") in the IPCC's model, because the measured rise in the atmospheric CO2 level is just half of that expected from the amount of anthropogenic CO2 supplied to the atmosphere; and carbon isotope measurements invalidate the IPCC's model (Segalstad, 1992; Segalstad, 1998).

The correct evaluation of the CO2 residence time -- giving values of about 5 years for the bulk of the atmospheric CO2 molecules, as per Essenhigh's (2009) reasoning and numerous measurements with different methods -- tells us that the real world's CO2 is part of a dynamic (i.e. non-static) system, where about one fifth of the atmospheric CO2 pool is exchanged every year between different sources and sinks, due to relatively fast equilibria and temperature-dependent CO2 partitioning governed by the chemical Henry's Law (Segalstad 1992; Segalstad, 1996; Segalstad, 1998).

Knowledge of the correct timing of the whereabouts of CO2 in the air is essential to a correct understanding of the way nature works and the extent of anthropogenic modulation of, or impact upon, natural processes. Concerning the Earth's carbon cycle, the anthropogenic contribution and its influence are so small and negligible that our resources would be much better spent on other real challenges that are facing mankind.

Tom V. Segalstad
Associate Professor of Resource and Environmental Geology
The University of Oslo, Norway
Personal web page:

Essenhigh, R.E. 2009: Potential dependence of global warming on the residence time (RT) in the atmosphere of anthropogenically sourced carbon dioxide. Energy & Fuels 23: 2773-2784.

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Murray, J.W. 1992: The oceans. In: Butcher, S.S., Charlson, R.J., Orians, G.H. & Wolfe, G.V. (Eds.): Global biogeochemical cycles. Academic Press: 175-211.

Revelle, R. & Suess, H. 1957: Carbon dioxide exchange between atmosphere and ocean and the question of an increase of atmospheric CO2 during past decades. Tellus 9: 18-27.

Segalstad, T. V. 1982: Stable Isotope Analysis. In: Stable Isotopes in Hydrocarbon Exploration, Norwegian Petroleum Society 6904, Stavanger: 21 pp. Available at: (Link)

Segalstad, T. V. 1992: The amount of non-fossil-fuel CO2 in the atmosphere. AGU Chapman Conference on Climate, Volcanism, and Global Change. March 23-27, 1992. Hilo, Hawaii. Abstracts: 25; and poster: 10 pp. Available at: (Link)

Segalstad, T. V. 1996: The distribution of CO2 between atmosphere, hydrosphere, and lithosphere; minimal influence from anthropogenic CO2 on the global "Greenhouse Effect". In Emsley, J. (Ed.): The Global Warming Debate. The Report of the European Science and Environment Forum. Bourne Press Ltd., Bournemouth, Dorset, U.K. [ISBN 0952773406]: 41-50. Available at: (Link)

Segalstad, T. V. 1998: Carbon cycle modelling and the residence time of natural and anthropogenic atmospheric CO2: on the construction of the "Greenhouse Effect Global Warming" dogma. In: Bate, R. (Ed.): Global warming: the continuing debate. ESEF, Cambridge, U.K. [ISBN 0952773422]: 184-219. Available at: (Link)

Solomon, S., Plattner, G.-K., Knutti, R. & Friedlingstein, P. 2009: Irreversible climate change due to carbon dioxide emissions. Proceedings of The National Academy of Sciences of the USA [PNAS] 106, 6: 1704-1709.

Stumm, W. & Morgan, J.J. 1970: Aquatic chemistry: an introduction emphasizing chemical equilibria in natural waters. Wiley-Interscience: 583 pp.

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