WHY THE OBSERVED ATMOSPHERIC CO2 INCREASE COULD BE NATURAL

The IPCC’s claim is that the CO2 in the atmosphere has originated from the burning of hydrocarbons and this has supposedly been confirmed empirically by observations of the ice-core and carbon isotope ratios. Anthropogenic CO2 is depleted in the isotope 14C and this has observed to have been decreasing in the atmosphere. 14C is continuously formed in the upper atmosphere from 14N through bombardment with cosmic neutrons and oxidized to 14CO2. The isotope 14C is not stable and decays with a half-life of 5,700 years. This means that fossil fuel CO2 isolated underground for thousands of years (away from processes that destroy the molecule) will be depleted in 14C. The change of 14C in atmospheric CO2 is measured as Δ14C which is the ratio of 14C containing CO2 molecules relative to 12C containing CO2 molecules compared to a standard material. The decrease of 14C in the atmosphere is an expected consequence of humans adding CO2 to the atmosphere because the CO2 we have emitted into the atmosphere comes from old CO2 in which the unstable 14C has decayed. Anthropogenic CO2 is also depleted in 13C. The argument goes that if humans are responsible for the increase in atmospheric CO2 then we should see these values decrease over time. And we do, as shown by the graph below.

But there’s a problem. The decrease in 13C and 14C cannot concretely be attributed to anthropogenic CO2. The measurements of decreasing 13C and 14C do not tell us whether the CO2 is anthropogenic or natural in origin. This is because a decrease in 13C and 14C is not a unique signature for anthropogenic CO2. For example, a decrease in 13C or 14C is equally consistent with the decomposition of organic matter derived from vegetation (biogenic CO2) or bacteriogenic methane (which oxidizes to CO2 and is very low in 13C) or volcanic CO2 which is depleted in 14C. Similar to anthropogenic CO2, biogenic CO2 is depleted in 13C and an increase from that pool would decrease δ13C values and an increase in volcanic CO2 would decrease Δ14C values. The IPCC tend to be very vague about the details of how we measure the change in the isotope composition of the atmosphere and it’s very easy for the uninitiated to get the false impression that climate scientists are able to clearly separate anthropogenic CO2 from natural sources. This is untrue and a few moments of reflection are probably enough to enable most people to appreciate the simple practical reason why it is not possible that such measurements are really taking place.

TABLE FROM THE NOAA

Despite the decrease in δ13C and Δ14C values not being a unique signature of anthropogenic CO2, the amount in the atmosphere can be approximated by the isotope ratios. For example, we can look at the δ13C value. δ13C is the difference between the ratio of 13C to 12C in a substance compared to a standard. The number is multiplied by one-thousand and expressed as per mil (parts per thousand) denoted as δ13C. Anthropogenic CO2 has an average δ13C value of -29 (similar to biogenic CO2 with a value of around -26). The assumed pre-industrial δ13C value was around -6.5 to -7 and the graph above shows that it has risen to a modern-value of -8.3. If the atmospheric δ13C value was -6.5 in 1850 (the generally accepted baseline value) and has risen since then to -8.3 this means that the amount of anthropogenic CO2 in the atmosphere is 8% because to arrive at a value of -8.3 there can only be 8% of anthropogenic CO2 in the atmosphere from an original value of -6.5 assuming anthropogenic CO2 has a δ13C value of -29. Therefore, the rest of CO2 in the atmosphere must be natural in origin. The 8% of anthropogenic CO2 in the atmosphere is only a crude approximation. If there were more than one source for the CO2 increase then the anthropogenic component could be more or less than 8% due to the anthropogenic signature being mixed up with negative and positive δ13C values of CO2-emissions from other sources.

According to Segalstad (1996) outgassing of CO2 from the oceans and volcanoes better explains the isotope change. The isotope change suggests a leaner 13C source such as oceanic and volcanic CO2. These sources have δ13C values of -10 and -5 respectively which are leaner than anthropogenic CO2 at -29. For example, from a pre-industrial δ13C value of -7, a 36% increase in oceanic CO2 in the atmosphere, a 2% increase in anthropogenic CO2 and a 12% increase in volcanic CO2 would change the δ13C value to around -8.3 (the same as what we observe in the atmosphere). This is just an example and these numbers can be played around with. Similar to anthropogenic CO2, volcanic CO2 is also depleted in 14C with a Δ14C value of -600 (Ronge et al 2016) and so an increase in CO2-emissions from marine volcanoes would leave a similar signature in the atmosphere as adding anthropogenic CO2. Volcanoes as a possible source for the CO2 increase has been suggested by Casey (2015) who calculates that marine volcanoes could be outgassing 400 Gts of CO2 per year. As the partial pressure of CO2 in the oceans increases due to the extra CO2 from marine volcanoes that would force more CO2 into the atmosphere. Assuming Henry’s law, 400 Gts of CO2 from marine volcanoes per year would contribute as much as 8 Gts to the CO2 increase, accounting for 50% of the annual CO2 increase of around 16 Gts.

The IPCC claims that we know the increase in CO2 is not coming from the ocean because absorption of anthropogenic CO2 from the atmosphere has acidified the ocean, supposedly indicated by the increase in ᴘCO2 and [H+] and the decrease in pH. However, ᴘCO2 can change due to things besides absorbing more anthropogenic CO2 from the atmosphere. It varies continually in accordance with a host of environmental parameters such as temperature, physical and biological processes (Macovei et al 2020). According to Jaworowski et al (1992) if all marine biology were removed from the ocean this would increase ᴘCO2 by 500%. Hence variations in marine biology alone could account for larger variations in ᴘCO2 than anthropogenic contributions from burning hydrocarbons at the current rate. Furthermore, increasing ᴘCO2 is not at odds with the oceans outgassing CO2, as long as the oceans have absorbed more anthropogenic CO2 than they have outgassed. The amount of CO2 humans have emitted since 1850 is estimated to be 2,000 Gts according to the IPCC and the increase in the atmospheric CO2 content has been over 900 Gts. Therefore, more anthropogenic CO2 must have been absorbed by the sinks (primarily by the ocean) than what has accumulated in the atmosphere. Of course, the oceans could still absorb anthropogenic CO2 if they were warming because the warming would not appreciably alter the 1:50 partitioning ratio.

HUMANS HAVE EMITTED ABOUT 2,000 GTS OF CO2 SINCE 1850

The mechanism by which the oceans could increase atmospheric CO2 is very simple. The solubility of CO2 in water depends on the water-temperature and so water will release CO2 when its temperature rises. Therefore, part of the observed increase in atmospheric CO2 could be the result of ocean outgassing in response to global warming. According to Segalstad (1996) a 12°C warming of the Benguela Current alone could increase atmospheric CO2 by 150ppmv. Humlum et al (2013) and Salby (2016) have shown a strong relationship between the CO2-emission rate and the global surface temperature, as shown by Salby’s graph here (with the vertical axis representing the annual growth of CO2 in ppmv and the blue line representing the global surface temperature). Humlum et al (2013) found that there is a one-year time-lag between temperature changes and corresponding CO2 changes, with temperature change preceding CO2 change, with the authors concluding: “A main control on atmospheric CO2 concentrations appears to be the sea-surface temperature”. The correlation between sea-surface temperature and the CO2 rise is strong. Endersbee (2008) has shown that if you plot the sea-surface temperature against the atmospheric CO2 rise at the Mauna Loa Observatory you get a correlation of 0.9959 (a very strong correlation which suggests that a cause and effect relationship exists).

The question is, is the assumed change in global temperature of 1°C enough to explain the assumed increase in CO2 of about 140ppmv due to solubility changes alone? And the answer to that question, would appear to be no. The Van’t Hoff temperature equation (shown here) can be applied to determine the approximate changes in CO2’s solubility due to changes in temperature. Where kH is Henry’s constant, kHpc is 29.41, exp stands for exponential, T is the thermodynamic temperature in K, Tº refers to the standard temperature in K (298K) and -C is -2400. When applying the equation, the partitioning ratio in response to changes in mean water-temperature is 1:40 at 20°C, 1:50 at 15°C and 1:60 at 10°C (rounded to the nearest whole numbers). So, the relationship is approximately linear between 10°C to 20°C, with the partitioning ratio being inversely proportional to the temperature. Assuming the oceans contain 40,000 Gts of dissolved carbon for simplicity (the IPCC’s figure is slightly less) and the atmosphere contains 800 Gts at 15°C, this implies that a temperature increase of 1°C would only be sufficient to increase the CO2 concentration by 40 Gts (carbon) corresponding to almost 19ppmv. However, there might be another factor that could increase atmospheric CO2 that is related to temperature, as yet undetermined, such as changes in biology. The idea that the CO2 increase could not be natural because the observed oceanic temperature increase cannot account for the increase in CO2 due to solubility changes is overly simplistic because the rates of absorption and emission depend on the displacement of the atmospheric/oceanic interface from equilibrium in terms of relative pressures. If the concentration of CO2 in the oceans increased for example this would force more CO2 into the atmosphere upon equilibrium.

Temperature-driven changes in the CO2 flux between the ocean surface waters and atmosphere may be invoked as a plausible mechanism to explain at least a substantial part of the CO2 variations over the last Millennium

Kouwenberg (2004)

Another reason as to why the CO2 increase is probably natural is because the idea that anthropogenic additions are adding to the CO2-greenhouse over hundreds of years is at variance with the implications of Henry’s law. This law determines how much anthropogenic CO2 will end up being added permanently to the atmospheric greenhouse in proportion to how much will end up being dissolved in the oceans when the process of dissolution is complete. In the IPCC’s AR4 carbon-cycle diagram, they show that anthropogenic CO2 molecules are being absorbed by the oceans and these molecules are then recycled back into the atmosphere and this recycled CO2 is adding to the CO2 increase. However, these cannot be the same molecules because once the original anthropogenic molecules have been absorbed by the oceans they become thoroughly intermixed with natural pre-existing CO2. These are just tagged as ‘anthropogenic CO2’ since that is how much the IPCC assumes the oceans can cope with. Since there is no logical reason to believe these are the same molecules there is no reason to treat them any differently from the natural oceanic emissions. It seems more probable that what the IPCC tag as ‘anthropogenic CO2’ re-emitted by the ocean in their diagram is simply naturally emitted CO2 that is contributing to the CO2 increase and that nearly all anthropogenic CO2 is being absorbed by the oceans as Henry’s law says it should be.

Henry’s law governs the solubility of gases in water and determines a partitioning ratio between the amount of CO2 residing in the atmosphere and the amount that will be dissolved in the oceans at a given temperature at equilibrium. At the current mean ocean temperature of 15°C that partitioning ratio comes out to be 1:50. This partitioning ratio implies that for every tonne of CO2 that is released into the atmosphere, only about 0.02 tonnes will remain there and the rest (about 0.98 tonnes) will be absorbed into the oceans. The absorption of CO2 into the oceans should occur rapidly too because the process of dissolution is fast. The fast absorption of anthropogenic CO2 is supported by the observations of Quirk (2009) who concludes: “The constancy of seasonal variations in CO2 and the lack of time delays between the hemispheres suggest that anthropogenic CO2 is absorbed locally in the year it is emitted. This implies that natural variability of the climate is the prime cause of increasing CO2”. So anthropogenic CO2 is absorbed rapidly, probably due to the fast equilibria of Henry’s law. As Callendar points out: “There is, of course, no danger that the amount of CO2 in the air will become uncomfortably large, because as soon as the excess pressure in the air becomes appreciable, say about 0.0003 atm, the sea will be able to absorb CO2 as fast as it is could be produced”.

The IPCC dismisses Henry’s law and the partitioning ratio on the grounds that it is superseded by the Revelle Factor which they allege renders the partitioning ratio null and void, although the Revelle Factor is hypothetical and contradicts Henry’s law. As Weber et al (2016) says: “The Revelle Factor is included in the elaborate models and is a resistance to absorbing atmospheric CO2 by the ocean. However, as Gloor (2010) underlines, there is no evidence for the Revelle Factor which is hypothetical”. The Revelle Factor suggests that the partitioning ratio for CO2 between the atmosphere and ocean changes with ᴘCO2 and as the relative concentrations of DIC shift and is the reason why the oceans cannot absorb very much CO2. The Revelle Factor arises due to the way CO2 is partitioned in the ocean. The idea is that because CO2 only makes up 1% of total DIC in the ocean and given that CO2 in the atmosphere and oceans exist in equilibrium then the ocean should only absorb a small fraction of our emissions. The expression for the Revelle is shown by the formula below. It expresses a proportional change in ᴘCO2 corresponding to a proportional change in DIC. The capacity of the oceans to absorb anthropogenic CO2 is inversely proportional to the value of the Revelle Factor and higher values will oppose anthropogenic CO2 invasion more than lower values. The average value of the Revelle Factor is said to be around 10 to 11 meaning the surface-ocean can only absorb 10% of an increase in atmospheric CO2 (excluding the biological pump).

The ocean capacity to take up additional CO2 for a given alkalinity decreases at higher temperature and at elevated CO2 concentrations (about 15% per 100ppmv — computed from the so-called Revelle Factor)

IPCC AR5

Take note there is no time-variable in the Revelle Factor formula and the total amount of CO2 water can absorb based on that formula remains constant over time until the relative concentrations of DIC change. Once again, Henry’s law governs the solubility of gases in water and states that at a given temperature the amount of a gas dissolved in water is directly proportional to its partial pressure in the air adjacent to the solvent at equilibrium. The law can be described mathematically as: p = kHc. Where p is the partial pressure of the gas above the solute, kH is the proportionality constant (i.e. Henry’s constant) and c is the concentration of dissolved gas in the liquid. The constant of proportionality for CO2 at the average surface temperature of 15°C gives us a partitioning ratio between the atmosphere and the oceans of 1:50 respectively. If the Revelle Factor were correct and the solubility of CO2 changed as the relative concentrations of DIC shifted (which occurs when the partial pressure of CO2 changes) then kH in Henry’s law (and thus CO2’s partitioning ratio) would not be a constant for a given temperature. Note that Henry’s constant (in the equilibrium state of the law) is the ratio of the partial pressure of a gas at the liquid interface with the concentration of that gas dissolved in the liquid. Hence the constant does not change with concentration. It is a linear law. This means that the partitioning ratio of a gas, including that of CO2, is unchanged by changes to the atmospheric mass and can be multiplied up proportionally for any specified concentration in ppmv. Obviously, this is in conflict with the Revelle Factor which suggests that the solubility of CO2 is affected by the relative concentrations of DIC as the partial pressure of CO2 changes.

Solubilities given for those gases which react with water, namely… CO2… are recorded as bulk solubilities; i.e. all the chemical species of the gas and its reaction products with water are included

The Handbook of Chemistry

The most bizarre thing about the Revelle Factor is that it implies that the oceans are absorbing anthropogenic CO2 molecules at a greater rate than naturogenic ones preferentially. In AR5, the IPCC estimate that human CO2-emissions amount to about 33 Gts per year and natural ones amount to 724 Gts per year. The Revelle Factor is said to be temperature dependent and ranges from 8 to 16, with 8 being in the coldest ocean waters and 16 being in the warmest near the equator. A Revelle Factor of 8 would give a partitioning ratio for CO2 between the ocean and atmosphere of 8:1 respectively and a value of 16 would give 16:1. The Revelle Factor maintains a relatively high value throughout the year (above 8). Despite this, the Revelle Factor still allows the oceans to absorb essentially all naturogenic CO2-emissions, amounting to 724 Gts per year. Simultaneously, the Revelle Factor is precluding the oceans from absorbing very much anthropogenic CO2, and only about 30% of our emissions are being absorbed annually. Without the transfer of CO2 down to the deep-oceans, this would only be 10%. The essential question at issue is, if the Revelle Factor maintains a relatively high value throughout the year, how can the oceans be re-absorbing the natural CO2 they are emitting? The natural CO2 would, like anthropogenic CO2, just accumulate in the atmosphere, because the Revelle Factor should apply to them both equally. This result implies some selective principle is at work. But how could the oceans discriminate between naturogenic and anthropogenic molecules of CO2 when they are all mixed up together in the atmosphere?

In AR5, the IPCC give figures of 3,120 Gts for the atmospheric CO2 mass, 745 Gts per year for natural absorption and 33 Gts per year for anthropogenic emissions. The IPCC’s figures give us a residence time of 3,120/745 = 4.2 years. This implies that the total amount of anthropogenic CO2 in the atmosphere before absorption is 33*4.2 = 138.6 Gts = 17.8ppmv (4.5% of the resident CO2-greenhouse). According to some, residence time is not necessarily a measure of how long it would take for anthropogenic CO2 to be removed from the atmosphere because if we added CO2 to the atmosphere then CO2 would get forced down to the oceans indiscriminately, i.e. that is to say that upon increasing the partial pressure with anthropogenic CO2, as a consequence natural CO2 would also get forced down to the oceans to restore equilibrium. Thus equilibrium may occur faster than the residence time and this is suggested by the lack of time delay for the distribution of CO2 between hemispheres. The bomb spike graph shows that the mixing time between hemispheres for anthropogenic nuclear 14CO2 (most nuclear tests were in the Northern Hemisphere) is a few years. Thus the lack of a similar time delay for current atmospheric CO2 increases (most anthropogenic CO2 is also generated in the Northern Hemisphere) as shown in Tom Quirk’s paper is a strong indicator that current atmospheric CO2 increases are mostly due to natural sources and that human CO2-emissions (not the original molecules) are absorbed faster than the residence time.

The equilibration between the CO2 concentration in the atmosphere and the dissolved inorganic carbon in the sea is very short (about three quarters of a year)

Jaworowski et al (1992)

In conclusion, it seems entirely reasonable to me that the observed increase in atmospheric CO2 could be the result of ocean outgassing in response to global warming rather than being due to CO2-emissions from industrialized human society with marine volcanoes also possibly contributing an unknowable amount (perhaps as much as 50% according to the calculations above). There exists good evidence that the CO2 increase is coming from natural sources, not humans. For example, there is a clear disconnect between the growth-rates for human CO2-emissions and the CO2 increase. The CO2 increase better tracks global temperature. Furthermore, according to the AIRS data, the highest CO2 concentrations are not over industrialized regions, but downwind of warm ocean waters, suggesting that the sea-surface temperature is regulating atmospheric CO2 concentrations. The IPCC’s claims about the sizes of the anthropogenic contributions to the atmospheric CO2-greenhouse have not been confirmed empirically by observations of the carbon isotope ratios. Those observations imply that there is only 8% of anthropogenic CO2 in the atmosphere which could be as low as say 1% assuming it has been mixed up with other sources. The isotope change from the observed CO2 increase is better explained by the oceans and possibly volcanoes (as explained above).

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