CO2 makes the Ocean More Alkaline

Yes, it’s true! (Hey, it’s in the wiki so it must be true! /sarc )


We have (bold added):

Alkalinity or AT measures the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. The alkalinity is equal to the stoichiometric sum of the bases in solution. In the natural environment carbonate alkalinity tends to make up most of the total alkalinity due to the common occurrence and dissolution of carbonate rocks and presence of carbon dioxide in the atmosphere. Other common natural components that can contribute to alkalinity include borate, hydroxide, phosphate, silicate, nitrate, dissolved ammonia, the conjugate bases of some organic acids and sulfide. Solutions produced in a laboratory may contain a virtually limitless number of bases that contribute to alkalinity. Alkalinity is usually given in the unit mEq/L (milliequivalent per liter). Commercially, as in the swimming pool industry, alkalinity might also be given in parts per million of equivalent calcium carbonate (ppm CaCO₃).

So most alkalinity is due to carbonate rocks and CO₂ in the atmosphere. But adding more CO₂ doesn’t make thing more alkaline:

Alkalinity is sometimes incorrectly used interchangeably with basicity. For example, the pH of a solution can be lowered by the addition of CO₂. This will reduce the basicity; however, the alkalinity will remain unchanged

So there you have it. CO₂ in the atmosphere causes alkalinity and adding CO₂ to a solution will leave the alkalinity unchanged.

“Paging (not a) Doctor Connolley to the wiki-Metaphor Enforcement Ward, STAT!”

Now, in reality, there’s a bit of a word game going on here. Or perhaps a “definition game”…

You see, in common use, “alkaline” is used to mean “basic” or “opposite of acidic”. That isn’t strictly correct; though often the two things, alkalinity and basicity, are ‘fellow travelers’ in chemical reactions, so folks commonly treat them as the same thing. They are not.

An acid is a proton donor (there are a couple of other definitions too, such as based on electron pairs or …) where a base is a proton acceptor. Alkaline does not mean that. It means a specific neutralization point related to carbonate. That difference makes all the difference in the world as it relates to CO₂.

Alkalinity can be measured by titrating a sample with a strong acid until all the buffering capacity of the aforementioned ions above the pH of bicarbonate or carbonate is consumed. This point is functionally set to pH 4.5. At this point, all the bases of interest have been protonated to the zero level species, hence they no longer cause alkalinity. For example, the following reactions take place during the addition of acid to a typical seawater solution:

The key point there being the pH 4.5 point. So adding CO₂ to sea water at present does NOT “increase acidity” as the ocean is not acidic, it is basic (being pH bigger than 7 toward the 8 basic side). More importantly, adding CO₂ also does not make the ocean “less alkaline” either! Yes, it’s true! (Hey, it IS in a wiki article…)

As a sidebar note: Freshwater clams and other shell formers are happy to make shells at pH up to 4.5 or so. Leads me to wonder if they care about pH or Alkalinity…

Addition of CO₂

The addition (or removal) of CO₂ to a solution does not change the alkalinity. This is because the net reaction produces the same number of equivalents of positively contributing species (H+) as negative contributing species (HCO₃- and/or CO₃²-).

At neutral pH values:

CO₂ + H₂O → HCO₃− + H+

At high pH values:

CO₂ + H₂O → HCO₃ ²- + 2H+

So there you have it. Next time a Warming “chicken little” screams at you about “ocean acidification” and CO2, just point out that the ocean is alkaline and adding more CO2 to the ocean does not change the alkalinity at all… and wait for it…

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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30 Responses to CO2 makes the Ocean More Alkaline

  1. LG says:

    @ E. M.
    Did you mean :

    At high pH values:

    CO2 + H2O → CO32- + 2H+

  2. E.M.Smith says:


    Still playing with the superscript / subscript unicode. I think I’ve got it right now… “Cut / paste” is fine… until WordPress swallows the super / subs… Only one of the “superscript 2″s in this list works with wordpress:

  3. LG says:

    E.M., Don’t you still have an extra H on the right side of the equation ?

  4. E.M.Smith says:


    It’s a straight “cut / paste” of the wiki (assuming you mean that bit at the end of posting) and it has “2” just like your comment. They look the same to me. At any rate, all the formulas are not mine, but wiki-quotes.

  5. omanuel says:

    There are several different definitions of acids and bases. One approaches the definition of oxidation and reduction.

    I.e., this topic may generate a lot if verbiage with little or no advancement in understanding.


  6. E.M.Smith says:


    Yes… But “the other side” has exploited all that “noise and fury signifying nothing” for a while now. This posting is about pointing out the same can be done by the Skeptic / “Nothing To Worry About” side as well. It’s about as much “education on what alkaline really means” as “humor”, so I’m not too worried if a lot of folks spend some time exploring what acid / base / alkaline all really mean; and maybe laughing a bit in the process…

    Also of note (a bit further down in that wiki on Alkalinity):

    Processes that increase alkalinity
    Anaerobic degradation processes, such as denitrification and sulfate reduction, have a much greater impact on oceanic alkalinity. Denitrification and sulfate reduction occur in the deep ocean, where there is an absence of oxygen. Both of these processes consume hydrogen ions and releases quasi-inert gases (N2 or H2S), which eventually escape into the atmosphere. This consumption of H+ increases the alkalinity. It has been estimated that anaerobic degradation could be as much as 60% of the total oceanic alkalinity.

    Processes that decrease alkalinity

    Anaerobic processes generally increase alkalinity. Conversely, aerobic degradation can decrease AT. This process occurs in portions of the ocean where oxygen is present (surface waters). It results in dissolved organic matter and the production of hydrogen ions. An increase in H+ clearly decreases alkalinity. However, the dissolved organic matter may have base functional groups that can consume these hydrogen ions and negate their effect on alkalinity. Therefore, aerobic degradation has a relatively low impact on the overall oceanic alkalinity.

    So in all the noise about ocean acidity and alkalinity and CO2; the reality may come down to anaerobic vs aerobic conditions… shades of that lunar driven tidal ocean overturning….

  7. omanuel says:

    I.e., to donate a proton is electrically equivalent to accept an electron.

  8. Ralph B says:

    Most people with pools have to learn some about alkalinity, it is critical for your pH and cl-. Low pH and low alkalinity is very bad for unlined concrete pools as it will dissolve your pool. low pH high alkalinity…no problem for clams or pool walls. optimum pH is like the ocean 7.2 but I don’t know what the TA or CA is of the ocean (I bet it varies all over).

    I just look at the ocean acidification mantra as the alarmists grasping at straws since the temp isn’t cooperating with their plan.

  9. R. Shearer says:

    The words “acid,” “acidity” and “acidic” are scarier than “alkaline,” etc. That is why those terms are used by alarmists, just as CO2 is termed “carbon,” even though it is not carbon, in fact it’s mostly oxygen.

  10. the sea is getting more alkaline, because: lots of calcium, magnesium, potassium, sodium is washed from the land into the sea every year – those elements are very alkaline, especially magnesium

    seawater alkalinity / pH8,3 is very alkaline because of the salt in the water – talking about the water getting acidic, first they have to get read of the salt from the seawater

    the only acidity into the sea is coming from the forest creeks / rivers – especially from the rainforest – should we cut all the rainforest? please read this:

  11. philjourdan says:

    Thanks to your article and the comments, I understand what is being said. But the Wiki equation is still wrong. That is not to say the output is wrong, but clearly the output does not equal the input. A proton is being added as well as an electron.

  12. omanuel says:

    In conclusion,


    Our beautiful, bountiful universe and humans could not be

    1. Orbiting around the Sun in 1543.

    2. Powered by the source of energy that destroyed Hiroshima in 1945.

    The scientific revolution began when we accepted #1.

    The scientific revolution ended when we refused to accept #2.

  13. p.g.sharrow says:

    This ocean acidification thing is all my fault.
    A number of years ago I was on the Scientific American site arguing with an ecoloon troll about AGW and I told him he was being conned, CO2 could not cause climate warming. That it was the solar activity that had had caused the apparent warming. The only thing that increased CO2 could cause was a slight acidification of water. I guess he listened as this ocean acidifying started up a bit later. ;-)
    He bragged that his NGO had over $200 million at his disposal to push this AGW message. I thought he was just hot air as the Red Cross, that year, had just had their best year ever and raised almost $80 million.
    Who would have thought? pg

  14. Graeme No.3 says:

    Sorry, someone has the wrong equations.
    Much CO2 just dissolves as a gas, and doesn’t affect the pH. This is an equilibrium and the amount dissolved is reduced if the temperature goes up. (Good for annoying alarmists by pointing out that IF higher carbon dioxide raises the temperature then it will reduce the “acidifying action”).

    When carbon dioxide reacts with water it tends to form bicarbonate ion with 1 hydrogen ion. If the disassociation goes further then you get carbonate ion (CO3 with 2 minuses) and 2 hydrogen ions (H+). The amount of carbonate ion formed is dependent on the pH, i.e. more carbonate forms at higher pH and less at a lower pH. Further the disassociation to bicarbonate is also pH dependent and stops around 5.5 pH.

    So if you take rainwater/ distilled water etc. and dissolve carbon dioxide it will become mildly acidic. However the pH doesn’t keep dropping as you add more carbon dioxide; you get an equilibrium around 4.5 pH.

    Sea water is different as it contains lots of calcium and magnesium ions which react with bicarbonate or carbonate ions and precipitate (practically) insoluble carbonates such as calcite and aragonite. (The reaction is affected by various other anions e.g. speeded up by borates as worked out by Revelle). You are left with hydrogen ions that reduce the pH. How much? An estimate is that 1900 ppm. of atmospheric CO2 could reduce the oceans to about pH 7.4, still alkaline.

    The carbonate precipitation reaction is itself reversible under temperature and pressure of CO2 (see calcite compensation depth or lysocline). This also gets alarmist knickers in a twist.

    Basically, you are quite right; rising carbon dioxide is never going to make the oceans acid.
    The idea is the result of people looking for something they can use to scare other people who are equally ignorant and gullible.

  15. Graeme No.3 says:

    I should have added that sodium bicarbonate forms a mildly alkaline solution. Around 8.2-8.3 pH at 80 grams per litre (near saturation). Sodium carbonate is much more alkaline and gets up above 11 pH, hence its use in alkaline cleaners.

    The hysterical claim that the oceans have gone 30% of the way to being acid is also garbage. This depends on the pH of the ocean declining from 8.0 to 7.9 (or 9.0 to 8.9 or 7.0 to 6.9) because pH is the symbol for the logarithm of the reciprocal of hydrogen ion concentration in gram atoms per litre, i.e. as there is more hydrogen ion the figure for pH gets smaller and being logarithmic the step from x.0 to (x-1).9 is 0.3.

    The whole idea as far as I can ascertain is based on a survey near Hawaii where it was claimed that the pH of sea water had dropped by 0.034 units between 1988 – 2004 (from 8.117 to 8.083).
    Leaving aside the absurd level of accuracy, and that the reported drop is about 7.5% not 30%, with the aid of a COMPUTER MODEL they were able to claim the 30% drop from pre-industrial times. I am sure that EMS would remind you that with computer models GI-GO.

    Lest there be any doubt remaining I point out that the White Cliffs of Dover were laid down in Cretaceous seas by marine organisms flourishing despite the CO2 level being as high as 900 ppm.

  16. Sera says:

    Adding CO2 to the oceans would make them more base, not more acid- I must have missed an argument somewhere. Always late to the garden party.

  17. p.g.sharrow says:

    Good job Sera. Clean rain water has a PH of 5. back in the “old days” before AGW their bugaboo was “acid rain” caused by industry. Global Weather Calamity! is their newest cry, man caused of course. pg

  18. p.g.sharrow says: ”Good job Sera. Clean rain water has a PH of 5”

    correction: clean rainwater is pH7 = neutral; not acidic or alkaline; but that rainwater is full of CO2 – rainwater becomes acidic from SO2 (which becomes sulfuric acid in contact with water), not from CO2

  19. Graeme No.3 says:

    p.g.s. and std. You are confusing 2 things.
    Clean rainwater is rarely pH7 because it absorbs CO2 in its fall.
    Try boiling the rainwater which will expel the carbon dioxide gas (see above about it being less soluble at higher temperatures) and after cooling it down measure the pH.
    Now try shaking the flask or bubbling air through it. Then when measure the pH again.
    The more shaking the lower the pH until it stops reducing.

    Acid rain was due to sulphur dioxide (sulfur for americans) supposedly mostly generated by coal and oil fires. That will drop the pH much lower than 5.

    It is the buffering action of the dissolved salts in sea water that stops the oceans from being “acidified”.

  20. p.g.sharrow says:

    Rain water is RAIN WATER. Boiled water is not rain water. Boiling water to drive of dissolved gases means it is no longer Rain Water. RAIN WATER is PH5 more or less. and is created in the atmosphere from the gasses that condense to create RAIN. Pure water is PH7, sort of, and will, over time, dissolve soda-lime glass. I hold a patent for a wet fume scrubber and a farmer and know a bit about water, acid & base and gases. Water is the most important ingredient that I work with. pg

  21. Graeme No.3 says:

    I am not arguing with you, although rain water can vary in pH until it is saturated. The suggested boiling was to demonstrate to stefanthedenier the action of CO2. He was confusing it with acid rain from the earlier attempt to start an environmental doom story.

    Yes, water will dissolve soda-lime glass (sodium hydroxide is even faster), which is why laboratory equipment is supposed to be pyrex glass. Even then there can be other effects as well to be taken into consideration when doing analytical work. A certain environmentalist got egg all over himself years ago when he found enormous amounts of cadmium and lead in rain water near coal fired power stations. So much so that they would have killed everybody within 40 km. radius.
    The water had extracted metal ions from the (red and yellow) pigments in the plastic corks he was using.

  22. Verity Jones says:

    You had me for a bit with the title.

  23. omanuel says:

    Today I am pleased to report that sixty-eight years (2014 – 1946 = 68 yrs) of magical, pseudo-scientific models are crumbling in the face of reality.

    That game is over. World leaders and their armies of pseudo-scientists have encountered a Higher Power.

    It is now time to rejoice,
    – Oliver K. Manuel
    Former NASA Principal
    Investigator for Apollo

  24. Jason Calley says:

    Graeme No.3 says: “Yes, water will dissolve soda-lime glass (sodium hydroxide is even faster), which is why laboratory equipment is supposed to be pyrex glass.”

    Water is amazing stuff. One form of naturally occurring glass is that of tektites — and yes, water will dissolve that glass too, given a few million years. Some of the tektites from Moldavia are almost nothing left but fluting.

  25. omanuel says:

    Thanks to a few brave souls like E.M. Smith, the real purpose of fudging global climate data has now been exposed:

    John F. Kennedy and his brother were two politicians who would not be bluffed into submission.

    Both were assassinated before Henry Kissinger and Richard Nixon conceded to the USSR and China in 1971 and ended the Apollo Space Program.

    The rest is history.

  26. Fish farmers understand that fish pee contains ammonia. UIA (Un-Ionized Ammonia) is highly toxic to fish. As little as one part part per million will kill “Rainbow Trout”.

    My fish farm used recirculated water so it was essential to control the ammonia concentration. I used a fluidized bed bio-reactor to convert the ammonia into nitrites (almost as toxic to fish as ammonia) and then to nitrates that the fish could tolerate at levels of over 5,000 parts per million.

    In order to reduce the stress on our fish we adjusted the pH or the water to enhance the concentration of the harmless ionized ammonia NH4+ while suppressing the toxic NH3. This required making the water less alkaline. While we never achieved got close to the acidic range (<7.0), lowering the pH was highly beneficial to the health of Rainbow trout.

    The panic about CO2 lowering pH makes no sense to me as a fish farmer given that a lower pH reduces ammonia toxicity for pelagic fish. Folks who worry about mollusk shells in an acidic ocean are deranged. Even with CO2 concentrations five times higher than today the ocean pH will still be greater than 7.0 (= alkaline) so mollusk shells won't dissolve.

  27. I spent a dozen years cooling high power magnets and RF amplifiers (up to 30 MW pulses) with water. Some of these devices operated at potentials of 10 kV or more so the water had to be non-conducting. The water was de-ionized and continually processed to gaurantee 20 Meg Ohms/cm^2 to minimize electrolytic effects.

    In spite of our best efforts, copper would migrate via our “Inert” cooling water. The migrating copper caused blockages that triggered shut downs. These events were infrequent but we were unable to eliminate them entirely.

  28. Tim Clark says:

    It’s Friday…..
    What’s the pH of beer??

  29. NomoreGore says:

    Not to mention that the entire concentration of CO2 in the atmosphere, let alone that which man contributes, is miniscule relative to ocean volume.

  30. Pingback: The IPCC WGII report is out – now the screaming begins anew | The GOLDEN RULE

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