The Royal Society has just issued a summary report on the effects of CO2 on the pH chemistry of seawater and aquatic organisms and ecosystems. In addition to its pivotal role in the atmosphere in the regulation of global climate, CO2 and its sister chemical species, HCO3– and CO32- comprise the carbonate buffer system which regulates the pH of seawater. The new report can be found here. Acidifying the ocean is particularly detrimental to organisms that secrete shell material made of CaCO3, such as coral reefs and a type of phytoplankton called coccolithophorids [Kleypas et al., 1999]. The ocean pH change will persist for thousands of years. Because the fossil fuel CO2 rise is faster than natural CO2 increases in the past, the ocean will be acidified to a much greater extent than has occurred naturally in at least the past 800,000 years [Caldeira and Wicket, 2003].
For those of you who look back on your freshman chemistry days with less than fondness, the acidity or pH of an aqueous solution is a measure of the concentration of H+ ions in the solution, with low pH meaning high H+ concentration. H+ ions are aggressive little guys, and too much H+ in water can burn the skin off your hand or make a coral limestone go fizz. The link between CO2 and H+ arises by the combination of CO2 and water, H2O, to form carbonic acid, H2CO3. An acid is a chemical species that releases H+ ions into solution, as does H2CO3 to form HCO3– and CO32-. Adding CO2 to water causes the pH to drop.
The pH of seawater is buffered by the chemistry of carbon, just as is the chemistry of blood and cellular fluids. The buffering action arises from the fact that the concentrations of the various carbon species are much higher than is the concentration of H+ ions. If some process tries to add or remove H+ ions, the amount of H+ ions required will be determined by the amount of the carbon species that have to be converted from one form to another. This will be an amount much higher than the actual change in H+ concentration itself.
Most of the carbon in seawater is in the form of HCO3–, while the concentrations of CO32- and dissolved CO2 are one and two orders of magnitude lower, respectively. The equilibrium reaction for CO2 chemistry in seawater that most cogently captures its behavior is
CO2 + CO32- + H2O == 2 HCO3–
where I am using double equal signs as double arrows, denoting chemical equilibrium. Since this is a chemical equilibrium, Le Chatlier’s principal states that a perturbation, by say the addition of CO2, will cause the equilibrium to shift in such a way as to minimize the perturbation. In this case, it moves to the right. The concentration of CO2 goes up, while the concentration of CO32- goes down. The concentration of HCO3– goes up a bit, but there is so much HCO3– that the relative change in HCO3– is smaller than the changes are for CO2 and CO32-. It works out in the end that CO2 and CO32- are very nearly inversely related to each other, as if CO2 times CO32- equaled a constant.
Coral reefs are built from limestone by the reaction Ca2+ + CO32- == CaCO3, where Ca is calcium. Acidifying the ocean decreases the concentration of CO32- ions, which by le Chatlier’s principal shifts the equilibrium toward the left, tending to dissolve CaCO3. Note that this is a sort of counter-intuitive result, that adding CO2 should make reefs dissolve rather than pushing carbon into making more reefs. It’s all because of those H+ ions.
CaCO3 tends to dissolve in the deep ocean, both because of the high pressure and because the waters have been acidified by CO2 from rotting dead plankton. Surface waters, however, are supersaturated with respect to CaCO3, meaning that there is enough Ca2+ and CO32- in surface waters that you could give up some, and still not provoke CaCO3 to dissolve. However, it has been documented that corals produce CaCO3 more slowly as the extent of supersaturation decreases. This is also true for planktonic CaCO3-secreters such as coccolithophorids and foraminifera. We should note that for coral reef communities, the acid ocean is only one problem that they face, and it’s not the worst. Rising temperatures are tightly correlated with coral bleaching events, the expulsion of symbiotic algae, often followed by death of the coral. There is a terrifying time-series of temperature and coral bleaching from Tahiti in Hoegh-Guldberg, 1999]. When you look at the temperatures that killed the coral, and project future temperatures, it looks to be all over for corals. Coral communities are also impacted by water turbidity, resulting from fertilizer runoff, and by overfishing.
Elevated CO2 levels also affect fish and other aquatic organisms, in part because of the decrease in pH, but also because CO2 is what heterotrophic organisms try to exhale. However, we should note that dissolved CO2 levels were substantially higher than today in the geologic past, and organisms were able to cope with this OK, so apparently there can be some acclimation of populations to higher CO2.
The natural pH of the ocean is determined by a need to balance the deposition and burial of CaCO3 on the sea floor against the influx of Ca2+ and CO32- into the ocean from dissolving rocks on land, called weathering. These processes stabilize the pH of the ocean, by a mechanism called CaCO3 compensation. CaCO3 compensation works on time scales of thousands of years or so. Because of CaCO3 compensation, the oceans were probably at close to their present pH of around 8 even millions of years ago when atmospheric CO2 was 10 times the present value or whatever it was. The CaCO3 cycle was discussed briefly in regards to the uptake of fossil fuel by the ocean, here. The point of bringing it up again is to note that if the CO2 concentration of the atmosphere changes more slowly than this, as it always has throughout the Vostok record, the pH of the ocean will be relatively unaffected because CaCO3 compensation can keep up. The fossil fuel acidification is much faster than natural changes, and so the acid spike will be more intense than the earth has seen in at least 800,000 years.
There are several feedbacks between decreasing the rate of calcification that organisms do in the ocean, and the carbon cycle. Removing CaCO3 from surface waters tends to raise the CO2 concentration of the waters (it should be possible for you to work that out for yourself based on the chemical reactions above). This is a negative feedback, tending to remove excess CO2 from the atmosphere, but it is a small effect. Decreasing the flux of CaCO3 to the sea floor tends to diminish the amount of CaCO3 that gets buried in sediments, which hastens the pH-recovery from the CaCO3 compensation mechanism. This may not be a small effect at all, but it is a slow effect: thousands of years.
Caldeira, K., and Wickett, M.E. Anthropogenic carbon and ocean pH. Nature: 425, 365, 2003.
Hoegh-Guldberg, O. Climate change, coral bleaching and the future of the world’s coral reefs. Mar. Freshwater Res.: 50, 839-8–66, 1999.
Kleypas, J., R.W. Buddemeier, D. Archer, J.-P. Gattuso, C. Langdon, and B. Opdyke (1999) Geochemical consequences of increased atmospheric CO2 on coral reefs. Science 284: 118-120.
It is difficult to acquire any sense of the magnitude of the problem being cited without any quantitative information. Had you intended for us to go to the report? If so, a working reference would have been helpful.
[Response:My apologies for the link. As to the bottom line, we are talking about changes to a fundamental part of the ocean carbon cycle, far outside the range of natural variability, that are irreversible and will last for thousands of years. David.]
Re: the acid spike
Why should we be concerned? Another way to put it: as reported by the New York Times British Scientists Say Carbon Dioxide Is Turning the Oceans Acidic,
So, there it is.
I guess this fairly well buries the idea of ocean burial of CO2
[Response:A difficulty with ocean injection is the intense pH change right near the injection location. You can minimize this problem by injecting the CO2 as liquid droplets that float or sink through the water column, spreading out the injection location, or by injecting from a moving ship that drives around. Releasing CO2 to the atmosphere is not an ideal ocean injection strategy either because the location of ocean injection is the surface ocean, where diversity is highest. Rau and Caldeira have published the idea of neutralizing the CO2 by reaction with a carbonate, like MgCO3, which would eliminate the acid problem and also retain the CO2 in the ocean, rather than allowing it to equilibrate with the atmosphere (with eventual 25% CO2 escape). I am personally far more optimistic about geological sequestration, injecting CO2 into saline aquifers on land. David. ]
Hello,
I haven’t read the full report yet but the acidification of the oceans stands to reason. I am a practising medical practioner and acid-base balance is a very important part of the homeostasis of the organism, and small alterations of this have some profound effects. Equally tropical fish tank hobbyists go to great lengths to preserve the correct pH, O2 concentrations etc. The more you look at how the planet works, the more you have to agree with James Lovelock’s Gaia hypothesis. The correct link is this http://www.royalsoc.ac.uk/document.asp?id=3249 – on this page click on the pdf download link. John Monro, New Zealand
The link to download the Royal Society report PDF can be found near the bottom of http://www.royalsoc.ac.uk/document.asp?id=3249
>These processes stabilize the pH of the ocean, by a mechanism called
>CaCO3 compensation. CaCO3 compensation works on time scales of >thousands of years or so.
and:
>Because of CaCO3 compensation, the oceans were probably at close to >their present pH of around 8 even millions of years ago when >atmospheric CO2 was 10 times the present value or whatever it was…
how many K’s of years would it take to present any evidence of current disturbance of pH balance to verify an assertion like this?
are there good evidences of CO2 levels being disturbed thousands of years ago (highly enough) to give us a signal like what is being implied here (at the present) or not?
I must be misunderstanding… I am drunk, so it’s a good probability. :)
[Response:We know the atmospheric CO2 history going back 400,000 years from the Vostok ice core. There’s a new ice core with CO2 going back 800,000 about which I heard a preliminary talk at a meeting last fall. The pH response of the ocean to this history we estimate using ocean chemistry models. The past CO2 changes took place on time scales of thousands of years, rather than hundreds of years such as is happening today. Skol! David]
Need a double arrow. How about ⇔ or ↔ ?
You get it typing “& hArr;” or “& harr;” without the space or the quotes. You might increase the font size on the arrow though. I assume you know how to do that. Of course chemists tend to use two arrows — one pointing left and one pointing right — for chemical equilibrium. There is no commonly supported character for that though pretty much any browser these days should support the arrows I provided. An alternative way would be to get an image of the proper double arrow symbol. If you do so please don’t forget to insert the alternative text:
" in chemical equilibrium with "—
Anti-spam: Replace “user” with “harlequin2”
I’m confused (this is not a criticism, I am easily confused). I know nothing about this issue, but I just came across a reference to Jacobson, Mark Z., “Studying ocean acidification with conservative, stable numerical schemes for nonequilibrium air-ocean exchange and ocean equilibrium chemistry.” J. Geophys. Res. Atm., 110, D07302, April 2, 2005.
The abstract says “… surface ocean pH is estimated to have dropped from near 8.25 to near 8.14 between 1751 and 2004…”
Given that a pH over 7 is basic, how is this an acidification? Looks like it is neutralizing. It also looks rather small.
[Response:You have this backwards. A pH LESS THAN 7 is acid. So 8.14 is more acidic than 8.25. Also, it is a logarithmic scale. A small change in the numbers is actually quite large in the chemistry. pH 7 is 10 times more acidic than 8. pH 8.14 is about 30 percent more acidic than pH 8.25 (because 10^8.25/10^8.14 = 1.3). – eric ]
How big do you think the buffer is? With any Acid-Base-buffer there is a limit up and down before the buffer is useless. Are there any findings on this, especially when we are speaking of huge areas such as an ocean.
Secondly, are there any fishs/plants that could take up CO2 or even need CO2 underwater to prosper?
Would there be an increase of those plants/fishs?
(Comparison: Lakes(algae population) < => O2 level)
[Response:This is a good question. The inventory of CO32-, the buffering agent, is about 2000 Gton C, which is about how much fossil carbon we are projected to release under business as usual by the year 2100. If we’re patient enough to wait 5-10 kyr, the buffer capacity is increased by the dissolution of CaCO3. In this case, have enough dissolvable CaCO3 in ocean sediments to neutralize about 5000 Gton of C, which is about all of the coal and everything else. See also response #14. David]
To make this post stronger, it would help to distinguish this acidification scenario from the concerns about acid rain that were so prominent about twenty years ago. You need to show that this problem is much worse than the previous problem because environmentalists lost credibility when it turned out the problem was much less severe than they said it was. Unless you can do this, people who are old enough to remember will tend to just assume a similar inflation of the problem is going on here as well.
[Response:I’m not convinced that acid rain is as benign as you say. It’s not a problem in the midwestern U.S. where I live because of the carbonate terrain that neutralizes acid, but it’s still a problem in the northeast, and in Scandinavia, and other places where the granitic terrain is less dissolvable. The acidification of the ocean is a much longer-term issue than acid rain, which goes away about two weeks after you reduce sulfur and nitrogen emissions from smokestacks. David]
I’d like to ask a general question: since the oceans are taking up about 1/3 of the anthropogenic carbon emissions, what is the opinion now of the scientific community about when the ocean surface layers will get saturated and this carbon sink (on relatively short timescales) will start to diminish? From what I’ve read, we’ve probably got several more decades to go… but what’s the latest stuff?
[Response:The ratio of dissolved CO2 to CO32- is about 1:10 preanthropogenic in tropical surface waters. The two will remain about inversely proportionate as CO2 rises. So double CO2, and you halve CO32-. I’d never thought about this in this way, but it sounds like the ratio of the two would reach 1:1 when CO2 reached about three times preanthropogenic, at which point the buffer is getting pretty weak. We should note that there are huge uncertainties with regard to changes in the circulation and biology of the ocean. David. ]
Re #2: The point touched-upon should perhaps be spelled-out: part of the problem with our carbon emissions is the time-accelerated nature of its onset and effects. When you have huge masses of gas and liquid sloshing around, it could get quite messy. Add 10 more miles-an-hour to hurricane speeds, and the taxpayers will be bailing out the insurance companies. The community of global warming deniers seems to the last man ignorant of “rates of change.” (On another, yet related, matter, they routinely discount that the NEXT doubling of Earth’s population is scheduled to happen in LESS THAN 50 years.) This same rapidity of warming, makes some free-market responses unlikely to be timely. Similarly, the rapidity of change is also one of the worst problems for wildlife species, including the aquatic, since humans are almost entirely oblivious to what is not happening in their immediate, manufactured habitat. As peoople learn more science, we may be in for a systemic paradigm-shift, 9.2 on the mega-Kuhnian scale.
This link, as cited in the sentence “The CaCO3 cycle was discussed briefly in regards to the uptake of fossil fuel by the ocean, here” is not working and should point here instead.
[Response:Thanks. Fixed now. David. ]
Re posts 8 & 3: I think only photosynthetic organisms gain a direct benefit from higher CO2, and fishes are certain not to benefit (although some fish species may be less sensitive to HCO3 than others and receive an indirect benefit via ecological interactions). Researchers sometimes use CO2 to anaesthetize or euthanize fish. Oceanic photosynthetic organisms are not limited by dissolved CO2, but by silicon, phosphorous, and nitrogen compounds. In fact, if you search “iron fertilization” on google I’m sure you’ll find lots of information about how iron makes more nitrogen available … actually now that I search it myself, it seems that iron is limiting and this is actually a way that some folks see us sequestering our excess carbon. The idea is to fertilize ocean deserts with iron and then the algal blooms will take up the carbon and sink it to the oceans’ bottom as their bodies settle out and slowly decompose. Hmm.
Deep ocean fish and other animals probably exist in a fairly high CO2 environment normally, but much higher concentrations from deep-water injections would likely be awful for them. As it is, many of these species are hermaphroditic (supposedly because it’s hard enough to find a mate, never mind one of the opposite sex), so I imagine having CO2 dead zones would only further jeopardize their chances. I guess the slowly decomposing algal masses would be less problematic.
Question: Have you folks looked at the LANL work in actual stripping of CO2 from the atmosphere via reactions with Ca or Mg solutions or thin films?
Aside from the obvious infrastructural challenges (billions of dollars in equipment and construction), does this idea have any serious merit?
It seems to me that this or similar ideas for actively trying to manage the atmospheric carbon content are probably the way to go, considering that the oceanic heat and CO2 buffer is essentially maxed out…what is your take?
[Response:I can’t speak to the economic part of the question, but thermodynamically, it’d be easier to capture the CO2 where it’s concentrated, say in the emission from an integrated gasification power plant, rather than fighting entropy by unmixing CO2 from the atmosphere. David. ]
Eric,
Your comment on #9 is rather confusing for a layman. A pH over 7 is alkaline, thus a pH change from 8.25 to 8.14 is less alkaline (and indeed more towards the acid side, but not directly “more acidic”). The amounts of CO2 involved indeed are huge to make that small difference in pH. What that implies for life in the oceans remains to be seen.
The change is fast too, but most species have much faster reproduction rates and may adapt to the new situation.
Most marine fish thrives at optimum in a 8.0-8.5 pH range in sea aquaria. Fish can tolerate a much wider range, but cannot tolerate a rapid change (in minutes, not centuries).
From NATURE 363 (6425): 149-151 MAY 13 1993:
“We find that 21 Myr ago, surface ocean pH was only 7.4 +/- 0.2, but it then increased to 8.2 +/- 0.2 (roughly the present value) about 7.5 Myr ago. This is consistent with suggestions that atmospheric CO2 concentrations may have been much higher 21 Myr ago than today”
Farther into history, during the Cretaceous the level of CO2 in the atmosphere was (depending of the source) 3-10 times current and temperatures were far higher. But that was the time that the forefathers of the current planktonic coccoliths made the white cliffs of Dover and thick carbonate deposits in many other places. Modern plankton foraminifera become inhibited below pH 7.6-7.8, thus only if some of these species recover their ability to grow in less alkaline, CO2-rich waters, then there will be no problem over the centuries to come. But plankton has a very high reproduction rate…
Re the response to my #9, no I don’t think I have it backwards. You (and the others) are using the term “acidification” to refer to a direction (lower pH) rather than a state change (becoming an acid), but the ordinary definition is “to make acidic.” To take an extreme case, it would seem odd to call a change from a pH of 14 to 13.8 an acidification, but maybe that is how the term is used in technical contexts.
This is important because I, and most lay people who read about this I am sure, thought the ocean was becoming acidic (and acids are dangerous). It is actually becoming less basic, or more nearly neutral, which sound rather benign. Thus it appears to be an emotional use of the term “acidification.” As a journalist I am sensitive to the power of such distincitions. It is analogous to calling CO2 “pollution” when it is also the global food supply. It may be technically correct but it is also misleading.
Second, do we really know the pH of the surface ocean in 1751 to 3 significant figures? I am curious how? Is there no regional or local or temporal variability, as there is with temperature? When someone says “estimated … near 8.25” I become curious about the uncertainties (that is my scientific field).
[Response:Yes, you have this right. It could be called “neutralization”, although (a) the change is demonstrably detrimental to calcifiers and (b) “neutral” has a connotation of “natural” which would be incorrect. I remember a shampoo ad when I was taking freshman chemistry, claiming it to be “low pH” which sounds better than “acidic”. David. ]
Re #9, a 30% change is large when the range is 100%. But in this case the range is more than a trillion percent, making 30% look small indeed. Logs are like that. I guess the question is whether there are significant processes that vary linearly with the pH?
[Response:Whether the dependence is linear or nonlinear is difficult to say, biological systems being as messy as they are, but the magnitude of the change is clearly significant, based on laboratory growth experiments. David. ]
RE#9&12,
Yes, to reduce pH alone is technically not “acidification.” It must be reduced below pH=7. The authors seem to be referring to any reduction in pH to be “acidification.” Or maybe they’re referring to a future pH<7 state, but I read recently something to the effect that a doubling of atmospheric CO2 over the next 100 yrs would only reduce the pH of the oceans by 0.24, so we’d be talking way, way into the future (if ever) before pH<7 conditions should exist.
Nevertheless, the problem of calcium carbonate dissolution exists above pH=7, so drops in pH are of concern even when the oceans are in a basic/alkaline state.
Re #12
Using the term acidification is not alarmist. This is a typical tactic of contrarians, casting any fact about anthropogenic climate change as extremist.
There is little variance in the ph of the oceans geographically and on the non-geologic time scale. Chemically, oceans are quite uniform. There are chemical differences in marine waters only in enclosed areas like estuaries that have reduced circulation with the open oceans. There is not uncertainty about this. Manufacturing uncertainty is another contrarian tactic.
Re #13
With acidification of the oceans, the biggest issue is it’s effects on ecosystems. Living things live in a narrow range of ph. Recent oceans and ancient oceans that allowed complex life had a ph that varied approximately from 7.5 to 8.5 and any change in ph occurred over extended time periods. Using the whole 1 to 14 ph scale to cast the acidification of the oceans as minor is intentionally misrepresenting the science. Misrepresentation is yet another contrarian tactic.
The change from 8.25 to 8.17 is significant because the effects it will have on the ecosystem, and the fact that this change in ph is much faster then past natural changes in ph makes it even more critical.
Re: #14 “With acidification of the oceans, the biggest issue is it’s effects on ecosystems. Living things live in a narrow range of ph.”
I finally got a chance to actually read the Royal Societies’ report. I was especially interested in Section 3 entitled Biological impacts: effects of changing ocean chemistry on organisms and populations. Obviously, the most important affects of ocean acidification would be on living organisms in the ocean thereby affecting primary productivity. This would have devastating effects on life on Earth. Any calls to reduce CO2 emissions would certainly be justified and compelling. But here is what I found instead from the conclusions section 3.8:
I could have quoted the whole page. Other than telling us that coral reefs (and Pelagic ecosystems) are in trouble — I have already kissed the coral reefs goodbye due to temperature increases alone — no firm conclusions were drawn about ocean acidification and its affects on ocean biology. Common sense (I know, often wrong) tells us that if the pH of the oceans drops 0.5 by 2100, then this is going to create serious havoc in the oceans. Yet this report, on the face of it, says no such thing and does not justify in any serious way its call for CO2 emission reductions.
So, as a strong advocate of CO2 emissions reduction to combat climate change, I’m a bit disappointed with this report.
[Response:I agree it’s hard to know how noticable the effects of acidification will be to the person in the boat or in the street, relative to all the other insults being visited on the oceans. I’d draw an analogy perhaps to ozone depletion, which seems like something a sensible planetary steward would prefer to avoid for precautionary reasons. Although (1) the effects of a pH change have been demonstrated in the lab, and (2) it’s a longer-term change than ozone depletion, which fixes itself on a time scale of decades after freon emission is stopped. David. ]
Re: #12.
David, acidification describes the lowering of pH, period, full stop. I suppose one could say “deBasification” or “deAlkalinization” or some such gobbledigook…but the technical term acidification and the usage of that term over the years in many, many branches of science justifies and supports its usage in this article.
Bases are also dangerous, and if you want to check, you could play with some lye or some pure bleach and see what happens.
The point is the range and the stable zone for current oceanic life-forms as they have evolved over the ages during which the ocean has remained stable within a very narrow pH range….the rates of change of that pH are very slow, both according to basic chemistry (given the composition of the ocean and its sheer volume), and according to available data from direct measurements and proxy measurements.
Question regarding the overall thrust of this article and the associated research:
The current understanding of the cycling of ocean water through the hydrothermal systems at the mid-ocean ridges indicates rather rapid flux based on chemical imbalances, heat flow and heat flux, and the abundance of apparantly primoridal 3He in seawater, specifically in the plumes of hydrothermal fluid rising above the ridges in many places – see the following references for discussions Johnson and Prius, 2003, Resing et al., 2004, Chavagnac et al., 2005, Locklair and Lerman, 2005, De La Rocha and Paytan, 2005,
Question – how does this cycling affect the action of the oceanic buffer? How should models of the oceanic carbon reservoir take these data into account? Are these cycles being incorporated into models of the oceanic circulation system with respect to the chemical/thermal budget?
[Response:Water reacts with igneous rocks in hydrothermal systems, exchanging some ions for some others. Relevant to ocean pH, Mg2+ is exchanged with Ca2+, essentially appearing to the ocean as a weathering flux. It’s a significant but not a dominant part of the ocean chemical regulation system. David]
Some recent new stories relating to this topic:
Patented technology captures carbon dioxide from power plants
Researchers from UCSC and … LLNL
coinventor Gregory Rau … with UCSC’s Institute of Marine Sciences … and LLNL researcher Ken Caldeira
… carbon sequestration method, called Accelerated Weathering of Limestone
http://currents.ucsc.edu/04-05/06-06/emissions.asp
Dirty Secret: Coal Plants Could Be Much Cleaner
http://www.tuscaloosanews.com/apps/pbcs.dll/article?AID=/20050522/ZNYT01/505220390
Can anyone comment on how significant CO2 is on oceanic pH compared to something like sulfur (either anthropogenic emissions or volcanic ones)? From the little tidbits I can find here-and-there, the effects of carbonic acid seem to be considered pretty minimal when it comes to the deterioration of coral, limestone, etc.
RE#20 (Joe), would using the term “acid ocean” in the title be alarmist when the ocean’s pH is clearly alkaline?
[Response:Acid rain, from sulfur emission, is a bigger deal for the dissolving of marble statues and acidification of freshwater lakes in igneous terrains (softwater). For the pH of the ocean, rising CO2 is more important. As for “acid ocean”, I personally like that phrase, even though it’s true it maybe pulls the strings a little. What about “ozone hole”? I’ve heard people assume that means a literal hole, in the atmosphere, through which people get sucked to space. Alarmist, yeah, OK, maybe, but I like it anyway. The facts are there. David. ]
I’m completely confused by this posting. It seems to defy basic chemistry. I quote
“Because the fossil fuel CO2 rise is faster than natural CO2 increases in the past, the ocean will be acidified to a much greater extent than has occurred naturally in at least the past 800,000 years [Caldeira and Wicket, 2003].”
But presumably, the carbonic acid of the ocean will be in chemical equilibrium with the CO2 in the atmosphere, and thus, for a given level of CO2, you get a corresponding level of acidity in the ocean. So I would think the acidity of the ocean would be the same as we had the last time CO2 was this high in the atmosphere. And if the ocean takes a long time to come to chemical equilibrium with the atmosphere the acidity would be less than if it were in equilibrium.
Please don’t get me wrong here. I’m not a climate change denier, and I can see that a fast rise in acidity in the ocean is much worse than a slower rise because a slower rise might give sea creatures time to adapt evolutionarily. I’m just trying to understand.
Thanks,
[Response:But if you wait thousands of years, CaCO3 dissolves to neutralize the higher CO2 levels. Higher CO2 means lower pH on short time scales, but on long time scales, knowing CO2 does not mean you know pH. David. ]
Re:#20 “Using the term acidification is not alarmist.”
Technically correct, but look at the the heading of the article “The Acid Ocean” — isn’t that just a teensy weensy alarming?
Strong alkalis are just as harmful as strong acids. Making comparisons to either is “extremist”. Increasing CO2 in the atmosphere may be causing the oceans to move from a more alkali Ph to a less alkali position. The timescale listed is over a century, and the endpoint it is still basic.
Please people, this stuff gets so blown out of proportion, try to remain calm.
Just a few quick comments on a few issues raised:
1. Definition of acid. There are many definitions of ‘acid’ and ‘acidic’. Some relate only to strong acids and bases, others include weak acids such as CO2. Some depend on titration, cations and anions, and others on the hydrogen-ion activity. Any definition is fine, as long as we are clear about what we are speaking. In my papers and the Royal Society report, we are speaking of acidity in the sense of a measure of hydrogen-ion activity (roughly, concentration).
Note that we typically say that a pot of hot water is cooling as its temperature decreases even though we might get scalded were we to put our hand into the water. The water is cooling even though it is still hot. Similarly, the oceans are becoming more acidic even though they are still basic. The addition of CO2 to the ocean increases the hydrogen-ion activity of ocean waters (decreasing ocean pH), and thus makes the oceans more acidic.
2. Sulfur. The increase of hydrogen-ion activity in the oceans from CO2 addition is orders of magnitude greater than that from sulfur addition. Global sulfur emissions are on the order of 5 x 10^13 g/yr; global carbon emissions (as CO2) are on the order of 7 x 10^15 g/yr.
3. CO2 not sole determinant of ocean pH. The pH of the ocean depends not only on atmospheric CO2 content, but also how much time that CO2 has had to spread through the ocean and interact with carbonate sediments, and how much carbonate and silicate rock weathering has occured on land. (The pH of the ocean depends on both the carbon and the alkalinity.) So, the comment by Peter assuming the CO2 in the atmosphere is the sole determinate of ocean pH is just wrong. Read Caldeira and Wickett 2003 or Caldeira and Berner 1999, or better yet, read one of Dave Archer’s fine papers on the topic.
http://eed.llnl.gov/cccm/pdf/Caldeira_Wickett_2003.pdf
http://www.sciencemag.org/cgi/content/full/286/5447/2043a
An interesting, somewhat related story http://www.eas.gatech.edu/research/abstract_0205b.htm
I am curious if anyone knows if the pH drop has been a steady decrease over time? Just two data points makes it hard to define a trend, and I would be curious to see if anyone has directly compared pH of the ocean with amount of CO2 emissions or CO2 present in the air. Maybe one could see the time delay from cause to effect, or see exactly how quickly the pH has dropped.
[Response:Tropical surface waters remain in pretty close equilibrium with the atmosphere, because they don’t mix with deeper waters, because they’re warm and buoyant. CO2 invasion, and hence acidification, of deeper waters is much harder to measure. A “measurement” is in effect a global survey of ocean chemistry, of which there are only a few. David. ]
Re #17 (and others): ‘Thus it appears to be an emotional use of the term “acidification.” As a journalist I am sensitive to the power of such distincitions. It is analogous to calling CO2 “pollution” when it is also the global food supply. It may be technically correct but it is also misleading.’ This “emotional use” is certainly the one I learned in high school chemistry. It would have been a little strange to dump an acid into a basic solution and say that one had made it either “more acidic” or “less basic” depending on the exact Ph after the addition of the acid. In fact, trying to apply tour terminology, I suppose one would be literally tongue-tied in the absence of a prior calculation of the final Ph. To be consistent, you should go after meteorologists for using the term “dry” to describe current drought conditions in southern Europe: As there is still some moisture, “less wet” is clearly the correct unbiased term. I’m sure that will make them all feel better, too.
Re #26: To quote from the post: “These processes stabilize the pH of the ocean, by a mechanism called CaCO3 compensation. CaCO3 compensation works on time scales of thousands of years or so.” The point being made is that there’s a more complex process involved, one that results (given enough time) in ocean Ph not decreasing in accordance with the amount of CO2 being added now. The basic reason is that it takes time for enough of the CaCO3 sediments to be dissolved to bring things back into balance. If this alkaline “liner” didn’t exist, then presumably you would be correct to expect much higher long-term acidity in proportion to atmosperic CO2 concentrations. Note that the idea of mixing CO2 with limestone as part of a deep ocean injection scheme (probably impractical for other reasons) is a shortcut to this natural process.
The Royal Society report summarizes all of this on page 8 and includes references for the details:
“As we outlined in Section 2.2.2, as atmospheric CO2 levels
increase so does the concentration of CO2 in the surface
oceans. However it is unlikely that the past atmospheric
concentrations would have led to a significantly lower pH in
the oceans, as the rate at which atmospheric CO2 changed in
the past was much slower compared with the modern day.
The fastest natural changes that we are sure about are those
occurring at the ends of the recent ice ages, when CO2 rose
about 80 ppm in the space of 6000 years (IPCC 2001). This
rate is about one-hundredth that of the changes currently
occurring. During slow natural changes, the carbon system
in the oceans has time to interact with sediments and stays
therefore approximately in steady state with them. For
example if the deep oceans starts to become more acidic,
some carbonate will be dissolved from sediments. This
process tends to buffer the chemistry of the seawater so that
pH changes are lessened (see section 2.2.3 and Annex 1 for
a more detailed review).”
Re #29: This is indeed interesting. Of course 1) isn’t SO2 itself a GHG?, 2) all of that SO2 production (largely from burning coal) is inextricably linked to the emission of large quantities of CO2, and is the fertilization effect even sufficient to mitigate for that CO2?, and 3) those dust storms are a consequence of a) climate change in northern China linked to reduced rainfall that may in turn have some relationship to all that pollution and b) are in any case being greatly enhanced by horrendous land use patterns that should be stopped ASAP. Also apropos the current discussion, I notice that the large storms are stated to be not useful for fertilization beacuse that have too much CaCO3 dust mixed in, but presumably that dust is itself directly useful in reducing acidification. Other than the direct effects of the desertification, I’ll bet all of this is very hard to quantify.
[Response: SO2 would be in the gas phase, but it condenses to small particles, which actually cool the planet by scattering visible light to space. With regard the rest of your questions, the feedback between climate, terriginous dust, and ocean fertilization, are speculative. David. ]
[Response: Actually SO2 is a mild greenhouse gas, however, this role is minor compared to the formation of sulphates and the cooling associated with them. -gavin]
Regarding #21, thanks for that Dave. But one thing that gets overlooked (in my opinion) is that primary and secondary productivities are not the only values in the ocean or any other ecosystem. Different species have different susceptibilities to environmental distributions. Salmon and some trout life histories involve moving between acidic and basic environs (my definition here is <7 and >7) when switching between fresh and salt water. They also tolerate changes in temperature relatively well. Not all species can do this so well. The variation among species (not just within them) will determine which are the evolutionary winners and losers. We may or may not threaten productivity with all this CO2, but we are definitely threatening a lot of species (possibly a lot of coral species, in particular). I’m not going to say that this fact means we have to change course; I’m just saying that the debate should include effects on the composition of the ecosystems and not just the ecosystemic processes.
Regarding post #7, there was a similar ‘experiment’ to the one we are now embarked on around 55 million years ago, at the end of the Paleocene period. Ocean acidification was extensive, and lasted a long time. See http://www.terradaily.com/news/climate-05zzp.html or look up ‘paleocene-eocene thermal maximum’ on the web.
[Response:One impact of the PETM was an extinction of calcifying organisms in the ocean. The amount of carbon released has recently been estimated to be comparable to the fossil fuel inventory, 5000 Gton C, based on the dissolution of CaCO3 on the sea floor. Recovery of the temperature took 100,000 years or so. The analogy is apt. David]
Re#31,
Maybe we’d become tongue-tied trying to say “more acid” or “less basic” rather than use the term “acidification.” However, as another poster suggested, “neutralization” may be a more appropriate term. It certainly doesn’t evoke the same emotional response though, does it?
We can leave the meteorologists alone. “Dry” does not only mean the absolute absence of moisture. For example, this internet dictionary http://dict.die.net/ includes in the definition of dry as “lacking natural or normal moisture.” I would say that a drought fits “lacking normal moisture.” Conversely, the definitions for acidification that I can find (such as at the same site) don’t seem to cover simply a drop in pH. But apparently its usage has spread beyond that of dictionaries.
RE#28,
CO2 emissions may be 100 times that of sulfur, but the resulting carbonic acid formed in water is much weaker than sulfuric acid! I have no problem ingesting large amounts of carbonic acid in the form of soda. “Natural,” unpolluted rainwater contains carbonic acid (pH=5.6). But I don’t plan on ingesting any sulfuric acid anytime soon, I’ve read about fog and cloud pHs of 3.0 or less, “acid rain” is usually considered that which has a pH<4, and I’ve seen what very dilute sulfuric acid can do to clothing. There’s also nitric acid from NOx releases (natural and anthropogenic) to be considered, too.
Is there any research evaluating these impacts on oceanic pH levels, or are they simply dismissed as negligible? And if they are dismissed as negligible, on what basis? A mass comparison of C vs S (or N) emissions alone seems very insufficient.
> geological sequestration, injecting CO2 into saline aquifers on land
Um, you do realize that these are inhabited?
By bacteria, yes, but that’s saying by the dominant form of life on the planet, and the one that does extensive lateral gene transfer.
Are we wholly comfortable with the notion of forcing bacterial evolution in this way?
The “biofilm” problem that has so plagued the oil and gas extraction industries, see here:
http://www.erc.montana.edu/
is the clogging of crude oil pipelines — which are rapidly filled up by the bacteria coming out of these underground areas, which even while being randomized and pumped are speedily reorganizing themselves into … something. We seem to have no clue what sort of structure or organization is being recreated — what they were doing down there (see Gould’s book, which was mentioned by Dyson here:
http://splorg.org:8080/lectures/dyson.html
and the subject of a recent AAAS discussion here:
http://php.aaas.org/meetings/2002_MPE_01.php
Of course I suppose we can hope they’d just find a way to turn the CO2 back into oil (grin).
Re: #21 and Steve’s comment #33
A good comment but in my view it’s all the rapidity of the acidification process. Phytoplankton may adjust in the 100 year period we are talking about and therefore primary productivity may not be affected all that much. However, as we move up the food chain, I think you can be sure that ocean species will be more and more affected by the lower oceanic pH due to their inability to adapt within the timeframe of the change. The highest ocean trophic levels are already under severe stress, mostly from human predation, but as we move down the trophic layers, we see that more and more stress is occurring there due to the same factors. The acidification of the oceans will accelerate this process by affecting food supplies. The fact that some species now (Salmon, some trout) already have this adaptation is not so relevant since presumably it took a long time for the adaptation to come about. The “variation among species”, in my view, may not have much affect since the species in question will be on the ropes and in some cases subject to extinction.
I’d be delighted if we’ve got any marine biologists reading here who want to weigh in on this subject
Well, I’m kind of a marine biologist (my BSc major about 10 years ago), and I think that we’re already fishing down food webs (search that with Daniel Pauly) so that’s hurting the higher trophic levels where we feed. But the fascinating (and scary) thing is that we are very quick to adapt, culturally, and we may end up just eating jellyfish and stealing krill from the whales. So that’s the end of the process and, here’s the point, I don’t think we have a clue about whether the acidification will get us there any earlier or later. The relationships between trophic level and rate of evolution isn’t very simple at all. Among sharks, generation time is lower in great whites than in dogfish (this should be checked, but I remember female dogfish maturing after 21 years); rockfish are lower on the food chain than tunas and also have a slower life cycle; etc. In the latter example, rockfish probably would evolve more quickly due to their coastal nature (close to freshwater inputs which fluctuate) and lower physiological demands. I’m suggesting that it’s quite possible that the acidification could actually hinder the simple selection pressures exerted by fishing.
The best case to argue for (fairly) direct negative effects on food supply may be for artisanal fisheries relying on small fish that make their homes in reefs. As reef species change this will affect the homes of the fish -> less diverse reefs would lead to less diverse fish communities -> less variety in available foods -> potential increases in variation in food productivity (lots of some kinds of fish in one season but nothing else in another season).
I’d also like to hear what marine biologists would think. I was stronger in evolution than ecology, and much stronger in those than in physiology. I did do one food analysis (involving ecological footprinting), however, demonstrating that the protein content that Japan receives from tuna could easily be replaced by a few hectares of soy. In conclusion, I don’t think that the food supply effect of ocean acidification is the strongest argument for reducing emissions.
About a year ago we had a conference at UNESCO on “The Oceans in a High-CO2 World”. The stated purpose of the conference was to summarize the research on sequestration and deep injection. What we realized was that in terms of the research that has been done, in terms of intellectual effort, the ranking is
1. Iron fertilization
2. Direct injection of CO2
3. Effects of high CO2 on organisms
What surprised us was that in terms of the really big uncertainties, the priorities ought to be reversed.The Royal Society report is really only the tip of the iceberg. The problem is that most of the studies that have been done look at acidosis (acid-base regulation) in the context of marine pollution. But CO2 isn’t just another acid. As a part of the calcium carbonate system it is actually a building block of shells and coral reefs, as a player in the metabolic system it can affect organismal health. There’s evidence that increasing CO2 levels could have serious impacts on coral reefs, decreasing calcification (evidence: experiments done in the Biosphere 2 coral reef). However, there’s also evidence that higher temperatures increase calcification.
In terms of higher trophic levels the real issue is likely to be food supply, not direct effects.
Re #21 Weakness of Royal Society report
The report was weak on biology because very few relevant experiments have been conducted. The basic conclusion is there is cause for concern, a precautionary principle suggests avoiding large perturbations to ocean chemistry, and we need to study this problem more.
We do not know what changing ocean chemistry will do to marine biota (other than some calcifiers) and especially we do not know what the long-term chronic effects will be on ecosystems. Experiments on echinoderms, for example, show great sensitivity of reproductive success on ocean chemistry changes but we do not know the potential for micro-evolutionary adaptation.
For some (e.g., the Bush Administration), uncertainty justifies inaction. For others, uncertainty implies risk and justifies action (both to reduce the proximate cause of risk [i.e., CO2 emissions] and the underlying uncertainty).
Re #31 (and #17, #9, etc) “acidification”
A common definition of carbonic acid is “a weak dibasic acid formed when carbon dioxide dissolves in water.” So, adding CO2 to seawater is equivalent to adding carbonic acid. Using the term ‘acidification’ to describe a process that introduces more carbonic acid into the ocean seems entirely appropriate.
“Neutralization” is usually used in the context of neutralizing the carbon acidity, for example, by the dissolution of carbonate minerals, thus using this term to describe what happens when CO2 is added to the ocean would be misleading.
Re #36 SO4 vs CO2 as it relates to ocean pH
The addition of 1 mol CO2 increases hydrogen-ion activity somewhat more than would a 1 eq reduction in alkalinity. So, to a first approximation each SO4 is about twice as effective at changing pH as a molecule of CO2.
Using the numbers from my previous posting:
Sulfate alkalinity = (5 x 10^13 gS) x (1 mol / 32 gS) x (2 eq / mol) = 3 x 10^12 eq
Carbon molar = (7 x 10^15 gC) x (1 mol / 12 gC) = 6 x 10^14 mol
Therefore, the potential for increasing hydrogen-ion activity from CO2 emissions exceeds that of S emissions by roughly 200. Even if you cut the CO2 number in half (e.g., not all will go in the ocean), we are still two-orders of magnitude bigger than the effect of sulfur emissions.
Re comment #36 by Mike Jankowski (+ small aside)
(Aside, for the record, I like most of the contributions of the skeptics on this site and in some cases they make very good points. Re “acidification” here and some comments in other strings, if this is really about the science, then let’s say exactly what we mean so as not to give any reason for contrarians to distract folks from the main, coldly scientific conclusion.)
Re #36 about sulfuric acid, smog doesn’t seem to disperse much out over the ocean. Would it be true that most sulfuric acid is neutralized by terrestrial buffers when it rains, thereby limiting its effect on ocean pH beyond just the constraints inherrent in its small concentrations?
Re#41/42,
I assure you that my discussion concerning the terminology of “acidification” has nothing to do with trying to distract anyone. The last line of my post #19 should make that clear. Some people are high on “political correctness,” and maybe I’m a little high on “technical correctness.” If acidification is accepted terminology for this situation, then so be it. I just wasn’t familiar with it’s use in this manner based on the definitions I had seen, and I recall the definition of a “neutralization reaction” (acid and base rxn producing water and a salt…in this case, calcium bicarbonate in the net reaction of acidic CO2 and the basic ocean, with the calcium bicarbonate produced in the reaction step of carbonic acid and calcuium carbonate) possibly being more appropriate.
My issue with SOx and NOx emissions affecting pH was a legitimate question and was also not meant as a distraction. I didn’t find much info on my own, and I felt this was a proper forum to raise the question before I delved into my own calculations (aside: I hated my water chemistry class).
Re#41: Thank you Dr. Caldeira for your prompt response.
Glad you are covering other non-GW harms from GHGs & measures that produce GHGs. This only strengthens our need to reduce GHGs & activities that produce GHGs. I have a sort of mental chart with lots of arrows: actions that produce GHGs (e.g., coal-burning) causing a plethora of problems (& goods – like power), acid rain, ocean acidification, local ground, air, water pollution, GW, health problems & dangers for miners, military threats/expenses (according to Pentagon studies re oil), etc.; and also many arrows of good (some bad) coming out of measures to abate GW. For example, bicycling/walking to offset some ICE vehicle transportation – reduces environmental harm, helps health & spirits, reduces crime (according to studies) & taxes to repair roads, but of course takes time & involves risks & is not always feasible. Moving closer to work is great, reduces env harm & stress from traffic jams, saves time for family benefit, etc. And these measures save money, including on health bills.
It would be exceedingly complex, but I’d hope some people are working on the total, all-factors picture.
Re my aside above: I meant to distinguish among the skeptics, whose input I value, and contrarians. I consider Jankowski to be the former, and thought the comment about the title of this post being alarmist (or at least sensational was a good one.) My comment was directed toward leaving even traces of alarmism out of AGW communications so that only the science can be attacked, which is much harder to do than attacking language. But now my comments are the distraction. Apologies.
Several entries speak of alarmist language (acidification, acid ocean), but no matter what the language people on the whole don’t seem very alarmed into taking even sensible, cost-effective actions to address GW & CO2 emissions. Environmental problems tend to strike much slower and less dramatically than terrorist acts, and are not as obviously linked to the causes. They just aren’t scary enough to cause frenzied reactions. That’s why movie-makers have to jazz up the threats – as in DAY AFTER TOMORROW (they won’t make much money off science documentaries of slowly creeping problems). However, it seems that environmental problems kill many more people than terrorists acts & threaten to escalate much more.
I remember a teacher asking us what if a lion had escaped from the zoo and was killing 4 people a day. We, of course, said everyone would be out trying to kill that lion. He then said, “Well, 4 people every day are killed in traffic accidents in our area, but people aren’t doing much about it.”
So anyway, from my perspective there can be no alarmist language re environmental problems – that is no language seems capable of alarming people into much action – certainly not the proverbial stampede in the movie theater. What motivates me is the desire to save lives, not alarm over threats to my own life.
So, go ahead use whatever “alarmist” language you can come up with. If I were a gambler, I’d bet it doesn’t cause any harmful, crazy reactions, not with environmental problems anyway.
My undergraduate degree was BS Marine Biology and I have been away from the field for several years, but I have kept up with the developments in marine biology.
The acidification of the oceans by anthropogenic CO2 does what any new discovery does in science, it brings up a series of new questions.
The direct chemical effect of CO2 on ecosystems is only one of several anthropogenic pressures on the ocean ecosystem. The anthropogenic effects include overfishing, pollution, habitat destruction and introduced species. Anthropogenic climate change will mean an increased average temperature for the oceans and possible changes in current systems that could locally amplify or reduce warming and can alter nutrient cycling resulting in changes in the amount of nutrients available for the growth of phytoplankton, the plant plankton that are the base of the food chain.
How all these effects will combine and impact the ocean ecosystem is an important but unresolved question. Will there be no combined effect (i.e. for the sake of argument lets say warming alone causes 10% mortality in a species population and acidification alone causes 10% mortality but combined warming and acidification still have just a 10% total mortality), a simple combined effect (10% warming + 10% acidification = 20%), or a multiplicative effect (10% warming alone and 10% acidification alone but when combined 50% mortality)?
Environmental changes like changes in ph in the oceans have occurred in the past and plants and animals have reacted to these changes. Adaptation to changed conditions does occur. This is basic evolutionary theory. When conditions change, some individuals within a population of a single species have genetic differences that give them the ability to survive the changes and they pass these characteristics to the next generation. However evolution theory also shows that many species are not able to adapt to environmental changes and become extinct.
A rapid rate of reproduction could mean a population can rapidly accumulate the genetic mutations that allow a species to adapt to a rapid environmental change. This would make it more likely for a species to survive a rapid change. However the fossil record still shows that even rapidly reproducing organisms have at times not been able to adapt and have gone extinct.
Many types of phytoplankton do increase their numbers rapidly but they propagate primarily by asexual reproduction, which makes it less likely for populations to accumulate the genetic mutations that could allow them to adapt. Complex marine organisms like fish usually have many offspring at each spawning event and because of this it is sometimes assumed that their rate of reproduction is rapid. This is not necessarily so. Most marine animals have large amounts of small and poorly developed offspring and do not exercise any parental care. Very few offspring survive but this is balanced out by having large numbers of offspring. The net result is under natural conditions these animals do not reproduce rapidly. Because they do not reproduce rapidly they are less likely to adapt to rapid environmental changes.
The effects on the ocean ecosystem cannot be determined only by examining individual species. This would assume that each type of organism is a completely separate entity, but in marine ecosystems there is a high degree of interdependence. If something happens to a population of one species other species and sometimes entire ecosystems can be effected. Acidification may negatively effect only a few species, but a reduced population of these species could have effects on other species that are otherwise uneffected by the increased acidity.
There are a lot of issues and the answers are unclear at the present time but are being examined. There were a handful of papers in Science and Nature in the past year or so that have examined the ecological effects of anthropogenic climate change on ocean ecosystems. There will be effects on the ocean ecosystem but it is unclear exactly what the effects and just how serious they will be.
One more comment on “acidification”
I was reminded today that Arrhenius’s original 1896 paper on CO2-induced greenhouse warming was titled “On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground.”
Maybe if we had kept on talking about adding carbonic acid to the air (instead of using the modern vocabulary whereby we add carbon dioxide to the air), we would have been talking all along about ocean uptake of carbonic acid and ocean acidification would have been an obvious consequence.
A question can be asked: are we in some way remiss in not returning to the language of Arrhenius? Would what is going on be clearer to the general public if we explain that we are releasing carbonic acid to the atmosphere?
Arrhenius, S. 1896 On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground. Phil Mag S.5 41 (251) 237-276.
Here’s a Canadian Fisheries and Oceans report on conditions off of British Columbia in 2004. I haven’t read it yet, but the abstract indicates that it’s mostly about warm water and associated species compositions.
http://www.pac.dfo-mpo.gc.ca/sci/psarc/OSRs/StateofOceans2004fnl.pdf
Coming a bit late to this topic, but
Re:#17 — Responding to “It is actually becoming less basic, or more nearly neutral, which sound(s) rather benign”. That would be due to a perception that the “normal” state of pure water is pH = 7, whereas the normal pH of ocean surface water is ~8.2. So using “acidification” to indicate a decrease in pH, particularly from a current “normal” state, seems correct and with an important connotation as well. See next paragraph.
Re: #19 — excellent points: that both (a) CaCO3 dissolution occurs above pH 7 (it depends on the H2C03, HCO3(-), and CO3(2-) equilibrium which determines the saturation state of seawater), AND (b) that biogenic calcification is made increasingly difficult when the saturation state of surface waters declines, which is what happens as rising atmospheric CO2 influences the chemistry of surface waters. Not just corals, but benthic foraminifera and calcareous algae may be affected.
Re: #39 — Soylent green is PEOPLE!