The Oceans are Absorbing Large Quantities of Carbon Dioxide

Alan Siddons recently pointed out that NASA’s James Hansen has been complaining that 44% of anthropogenic CO2 goes missing EACH YEAR, but CDIAC’s data clearly show that the situation has become far worse than that from the alarmist viewpoint.  Alan Siddons found when looking at the CDIAC 2016 Global Carbon Project spreadsheet, under the Historical Budget tab, that he could graph both the annual increase in gigatons of carbon for the atmospheric CO2 concentration growth and for the change in carbon in the Ocean. The values to be discussed here do not resolve man's contribution from natures contribution.   They are total changes in carbon dioxide in each case. The resultant profile was not what he expected.  The additional carbon dioxide dissolved in the ocean in red is compared with the additional carbon dioxide in the atmosphere in Alan Siddons plot below.

Since a shallow minimum in about 1840, the amount of the increase in the ocean concentration of CO2 has increased almost every year.  Generally the atmospheric concentration of CO2 has increased except for two brief periods of reductions around 1820 and 1856.  There was a strong decrease in the amount of the increase centered on about 1946.  Because the surface water layer of the oceans is attempting to come into equilibrium in dissolved CO2 content with the atmosphere, but there is substantial exchange between the warm surface layer and the colder ocean depths, the general increase in CO2 in the atmosphere since the end of the Little Ice Age will result in more dissolved CO2 in the ocean for a given surface temperature for a long period of time.

In 2004, the additional CO2 dissolved in the oceans and other waters of the Earth was a bit more than 60% of the additional carbon dioxide in the atmosphere, not the 44% that was already so high in James Hansen's mind as to be a troubling indicator of the disappearance of CO2 that he expected to remain in the atmosphere.   For him, this disappearance was a problem with respect to the catastrophic man-made global warming hypothesis with its claims that man's emissions of CO2 from fossil fuel use and the making of cement would leave that CO2 in the atmosphere for a hundred years or thereabouts.  Basically, these high atmosphere residence times are threatened by the high solubility of CO2 in water and the overturn of the surface layer of water with colder water from below.  At 25°C, CO2 is about 26 times more soluble in water than is molecular oxygen.

We are told by the settled science that increased atmospheric CO2 causes warming.  Yet, everyone knows that a warming ocean should release CO2, thereby adding to the CO2 in the atmosphere.  If that picture is right, do we not expect the ocean to act like a source of further CO2, rather than a sink, because CO2 in the atmosphere is supposed to warm the oceans?

Perhaps not.  Let us examine this exchange or equilibrium condition for CO2 between the ocean and the atmosphere. The mole fraction of a gas, X, dissolved in water is given by 

X = (v/RT) e^H/RT P,

where v is the free volume occupied by a mole of water, T is the temperature in Kelvin, H is the heat of vaporization of the gas from water, P is the partial pressure of the gas over the water surface or in the atmosphere, and R is the gas constant, as in the Ideal Gas Law equation PV = nRT, where n is the number of moles of the gas and V is the volume of the gas.  The mole fraction is the number of dissolved gas moles in the water divided by the sum of the number of water moles and the number of gas moles.  For the low pressure cases we will be examining, the denominator is essentially the number of water moles since the number of gas moles will be much, much smaller.

Because the mole fraction of the dissolved gas decreases as the temperature increases in this formula at constant P proportional to (P/T) e^H/RT , it is commonly assumed that changes in the temperature are the dominant control knob with respect to the solubility of CO2 in the oceans.  But, note that a change of the surface temperature of 0.7°C from 14.65°C to 15.35°C 

means that the ratio of the temperatures on the Kelvin scale is only 288.50K/287.80K = 1.00243.

For the sake of this thought experiment, let us assume, albeit wrongly, that the increase in atmospheric CO2 since 1850 has caused a 0.7°C or 0.7 K temperature increase as the atmospheric concentration of CO2 went from 280 ppm to 400 ppm. Then a 0.7 K temperature increase to present temperatures would be due to about a 120 ppm increase in CO2 concentration using a linear relationship as the alarmists are wont to do.  It would actually take more of a CO2 increase than that due to the logarithmic saturation of the CO2 absorption of surface thermal radiation  with concentration, but let us use their numbers anyway. The present to 1850 ratio of CO2 atmospheric concentrations is 400 ppm /280 ppm =1.43 or a 43% increase in the partial pressure of CO2 in the atmosphere.

The Handbook of Chemistry and Physics, 96th Edition, has a table for the solubility of carbon dioxide in water.  With a 5 kPa partial pressure of CO2 it says the mole fraction of CO2 is

10°C, X = 0.000048 = 48 x 10^-6

15°C, X = 0.000041 = 41 x 10^-6

20°C, X = 0.000035 = 35 x 10^-6

Let us examine the rate of change of the mole fraction with temperature, while holding the pressure constant.  From 10 to 15°C, the rate of change is a decrease of 7 x 10^-6 / 5 K and from 15 to 20°C, the rate of change is - 6 x 10^-6 / 5 K.  Thus at about 15 C, the rate of change is about - 6.5 x 10^-6/ 5 K = - 1.3 x 10^-6 / K.  All of this is for the partial pressure of 5 kPa.

There are 101.325 kPa in one standard atmosphere.  A partial pressure of CO2 of 400 ppm is then (0.000400 atm.) (101.325 kPa/atm.) = 0.0405 kPa. Since the mole fraction X is proportional to the partial pressure of CO2 in the atmosphere, the mole fraction X at 0.0405 kPa is much lower than this lowest partial pressure in the Handbook of Chemistry and Physics table of solubility.  We have

X = [0.0405 kPa)/ (5 kPa) ](0.000041) = 0.332 x 10^-6 

at 15°C.  The rate of decrease of X near 15°C with a temperature increase at the partial pressure of 400 ppm at a temperature of 15°C is then  

dX /dT = [0.0405 kPa)/ (5 kPa) ] ( - 1.3 x 10^-6 / K) = - 0.0105 x 10^-6 / K.

If we increase the temperature by 0.7°C as it has been claimed is the case since 1850 for the Earth's surface temperature, then near 15°C the decrease in X due to the temperature increase is about ( 0.7 K ) ( - 0.0105 x 10^-6 / K) = - 0.0074 x 10^-6.  Consequently, the mole fraction X after the temperature increase is about 

X = 0.332 x 10^-6  - 0.007 x 10^-6  = 0.325 x 10^-6 

due to the temperature increase of 0.7 K.  The mole fraction was therefore reduced to 97.9% of its prior value by the 0.7 K temperature increase.

But, when increasing the temperature, the partial pressure of CO2 was increased from 280 ppm to 400 ppm, an increase in the partial pressure by a factor of 1.43.  Since the mole fraction is proportional to the partial pressure of CO2, this means the mole fraction was increased by 43%, which is vastly larger than the 2% decrease due to a 0.7 C temperature increase.

Consequently, for the conditions on Earth, the oceans are a strong sink for CO2 as the CO2 concentration in the atmosphere increases.  What is more, increases in the concentration of CO2 in the atmosphere lead to smaller and smaller increases of the absorption of the Earth's surface thermal radiation, but the solubility of CO2 in the oceans and other waters of the Earth's surface remains proportional to the partial pressure of CO2 in the atmosphere. Thus, for a given increase in the absorption of the Earth's surface radiation or contribution to a temperature increase by that saturating mechanism, more and more CO2 will be absorbed by the oceans for any increase the absorption of surface thermal radiation.

The data that Alan Siddons plotted above shows this effect, much to the consternation of James Hansen.  The more CO2 you put in the atmosphere, the more gets sucked out of the atmosphere by the oceans and water generally, including even water bound up in minerals or soil.  The solubility of CO2 is proportional to its partial pressure, which has increased greatly, while temperature changes measured against the absolute Kelvin temperature scale are very small.  The more CO2 you put in the atmosphere, the less effect it has in absorbing further thermal radiation from the Earth's surface.  The atmospheric CO2 concentration changes are dominant compared to the temperature changes in solubility, which helps to stabilize the atmospheric CO2 concentrations and the resulting temperature.

But it is even worse than this for the alarmist cause, because Alan Siddons made another extremely critical discovery when examining the government's data on CO2 emission increases by man and comparing those annual increases with the government data on the annual increases in the atmospheric concentration of carbon dioxide.  He discovered that man's carbon dioxide emission increases each year were a small fraction of those due to natural causes.  Man's emissions are only 4 to 5% of the total annual additions of CO2 to the atmosphere averaged over the period back to 1960.

Now, one's first thought about where the huge natural CO2 emissions are coming from would be that it might be the oceans, but as we saw above, the oceans are a large sink for added CO2.  They are not the source. Things are getting mighty interesting!  Scientists clearly need to spend more time learning about nature and a little less trying to damn mankind.  Unfortunately, they are clearly being paid by most governments and the UN to make a case, no matter how, that mankind is evil and determined to destroy the planet.

Of course, some of the alarmists will say, see the oceans are acidifying and isn't that just awful.  But, ocean plant life, mollusks, and coral reefs consider CO2 as much food and construction material as do land plants. They actually thrive on what is still an alkaline ocean with plenty more CO2 for shell building, reef building, and plant food.  On this subject, see: 

Washington Post and Published Research Falsely Report Largest U.S. Reef Dissolving Due to Increased CO2