Ocean acidi what?

Guest essay by Steve Burnett

I have followed Wattsupwiththat for a long time, only posting occasionally if I feel an article or presentation is biased, or if there seems to be some sort of data misrepresentation. I choose to follow watts simply because there is less bias and far more numerical analysis of papers than most other climate news sources. I would certainly consider myself a climate sceptic, but my scepticism is part of everyday analysis for me, I simply don’t believe someone unless they show me the evidence.

It is evidence that is lacking for me on the warmist side of the argument; we simply don’t have a temperature record which is accurate, or long enough to infer some sort of anthropogenic effect. Proxies offer a decent long term view but are poor analogs for climatological variations in the past 200 years or so. Anyone who has worked with computer models should know, they are more likely to display what you want them to display and should always be taken with a grain of salt. Luckily I don’t have to make those arguments; there are plenty of other commentators with better credentials to make those arguments for me. I am but a lowly chemical engineering graduate, who has found neither a job nor academic position in this economy.

Within the past few weeks, a post went up which seemed more interested in ridiculing the author than refuting the claims. I was shocked, and I waited, at first it was a few days, then I let a week pass. All of those people who were more credentialed than I were silent. Certainly there was a comment on Henry’s law but nothing going into the necessary depth for refutation of the claims for doom surrounding ocean acidification. Unfortunately it’s a refutation that we need. Ocean acidification is the carbon controllers pinch hitter, the ace up their sleeve, or other analogous win card.

It’s easy to refute global warming and associated doom based on the contradictory evidence. In the case of ocean acidification its associated doom mechanism is much more difficult. To tackle ocean acidification you need to understand chemistry; pH, alkalinity, buffers, strong vs. weak acids. But you also need to grasp the math; Henry’s law, pH. and equilibrium constants. That’s why most of the time ocean acidification comes up as the last line of defense for carbon controllers, you might not understand it, but neither do they.

Before I begin I would like to acknowledge a couple of points

1. The oceans are acidifying

2. it doesn’t mean anything

If you’re not familiar with the argument here is a video produced from NOAA

http://www.youtube.com/watch?v=xuttOKcTPQs

This is an excellent reference point for us; it clearly and concisely lays out the argument. However it waves a hand over the how in favor of visual demonstrations. I will deal with these later but for now let’s talk about the processes underlying ocean acidification.

I have performed several laboratory experiments regarding CO2 and water. The first was to take a sample of river water and start mixing in atmospheric CO2. Using this method we were eventually able to overcome the buffer capacity of water and reached a pH of about 6.3. In another experiment we had a CO2 stripping column with water coming down the column and air with a variable CO2 feed going up. This experiment had already been run multiple times throughout the semester without a water changeover. Because of this my lab partner and I saw higher CO2 concentrations in our outlet stream than our inlet as the CO2 would off gas at anything below 19% concentration which was just slightly below the maximum feed we could add to our column.

To understand acidification you have to understand a little bit about mass transfer. Within a homogenous fluid, that is at equilibrium diffusion essentially forces and maintains an evenly distributed concentration. Whenever there is an interface such as an air to liquid separation then diffusion will occur across the boundary dependent on partial pressures. A partial pressure in the atmosphere can be determined by the system pressure * the percentage of atmospheric composition.

As gasses, even dissolved ones, are heated their pressure goes up, increasing the partial pressure of the material dissolved in liquid. for fixed concentrations heating will increase outgassing and cooling will increase ingassing. We know that the relationship between the amount of gas dissolved in a liquid is directly related to partial pressure so we know the relationships between liquid and gas concentrations at equilibrium will be linear with a modification to the coefficient based on temperature. This is represented by Henry’s law

p.a=k.ha*x.a Equation 1.

with the correction for the henry’s coefficient being denoted in equation 2

K.h(t)=K.h(t.0) *e^(-c*(1/t-1/t.0)) Equation 2

Of course this tells us nothing about pH, but chemistry does. pH was first conceived in 1909 by S. P. L. Sørensen. It was revised in 1924 to be used with electrochemical cells. pH represents the negative log of the hydrogen Ion concentration in solution. So at pH 7 your water has roughly 1*10^-7 moles of hydrogen ions per liter. at pH of 8 there are 1*10^-8 moles/liter of hydrogen ions. commonly the scale extends from 0-14, however pH can go into the negative range and exceed the boundary range of 14. We measure pH through electrochemical cells using the nernst equation. Seen as equation 3, R is the gas constant, T is temperature and F is the faraday constant.

E=E0-2.303*RT/F *(pH) Equation 3

pH meters aren’t simple devices. Essentially the Nernst equation measures electric potential, and plots it with respect to pH. To calibrate these instruments ideally we measure the voltage at a known pH and then at a secondary pH correcting for the slope. There are however so many things that can go wrong in a pH measurement that it is more suited to simply getting an idea of the pH rather than take a reading as gospel.

First a pH meter must be stored so as to maintain a liquid layer over the glass bulb, or else it doesn’t read pH properly. Secondly the Ionic fluid in the meter must be maintained or replaced periodically; otherwise the pH meter is likely to have a poor slope. Calibration solutions should closely match the pH of what you’re trying to measure as the linear slope is only a reasonable approximation within a few pH units. If you aren’t simultaneously measuring temperature and pH in both your buffers and the desired fluid temperature corrections can be off. In short it’s far easier to measure a 1pH unit change than a .1 and .01 and smaller increments are virtually impossible to reliably measure.

So how do we go about acidifying oceans from CO2? for that we have to consider chemical equilibrium. All CO2 dissolved in water will essentially form carbonic acid, given enough time, most of it will change back into CO2. the rate at which CO2 is converting to carbonic acid and carbonic acid back to CO2 eventually balances out so that If we know our CO2 concentration, we can know our carbonic acid concentration as well. The amount of carbonic acid in freshwater is roughly 1.7*10^-3 in pure water and 1.2*10^-3 in seawater. There is substantially less carbonic acid in seawater. So why are we concerned about ocean acidification when rivers and streams can hold more CO2? They also get direct carbonic acid from their rainfall sources. Equation 4 shows the conversion.

CO2+H2O → H2CO3–> CO2 + H2O Equation 4

Carbonic acid does not however make the water more acidic easily. Don’t forget that pH measures the concentration of hydrogen ions in solution. So of the 1.2*10^-3 moles of carbonic acid/ mole of CO2/liter only 2.5*10^-4 moles/mole/mole of hydrogen Ion are produced. This forms the bicarbonate Ion.

H2CO3- → H+ + HCO3- → H2CO3 Equation 5

Because weak acids and weak bases vary back in forth during equilibrium they make excellent buffers.

A buffer is a solution made up of one or more weak acids and bases that can be created to hold a desired pH. Essentially because the weak acids dissociate more frequently with a base present in solution and weak bases with an acid, you can hold the pH of a solution relatively stable. Your buffers pH will only change when you have consumed your entire weak acid or weak base.

The bicarbonate Ion can further dissociate but only 4.69*10^-11 of those ions do so. Now the Rub for the ocean acidification = ecosystem collapse comes from a third reaction in equation 6.

Ca(CO3)2 + 2 H+ → Ca2+ +2HCO3- Equation 6

For some it may not be baffling but let me explain the humor. Calcium carbonate is supposed to react with the Hydrogen atoms to form a free calcium Ion and 2 bicarbonate ions. But wait, the equilibrium concentrations are still going to hold. So as CO2 increases, carbonate Ions the ions “under attack” by ocean acidification WILL ALWAYS INCREASE IN CONCENTRATION!!!!.

But how does that relate to biological organisms. In short anything that needs to make use of carbonate will benefit from an increase in its supply. But there is actual math here too. Behold the Monod equation for microorganism kinetics. U is the specific growth rate, umax is the maximum growth rate, s is the concentration of the limiting substrate and ks is the value of u where u/umax is .5.

u=umax*(s/(k+s)) Equation 7

Essentially what this states is the growth of an organism is tied to the limiting nutrient. So we can conclude that as CO2 increases, Carbonate ions increase, which means that the limiting nutrient for shell production cannot be carbonate. If it was, then an increase in CO2 would correlate to a similar increase in growth for the carbonate dependent species. In the event that carbonate was in such comparative excess there is no conceivable means for the species to be struggling as all of the aqueous carbonate would be consumed at a substantially higher rate than CaCO3 precipitate.

All of this is ignoring the buffer capacity of the oceans; it is immense and tied strongly to the carbonate system. While you can increase the amount of carbonic acid in the sea, in order for CO2 to induce a pH change you would need a massive amount of it both dissolved in the ocean and with a high concentration above in the atmosphere. It is essentially chemically impossible for ocean acidification from CO2 to induce harm on carbonate dependent species. Before we can ever truly figure out whether or not CO2 is causing a problem we need to know the rate the shells are dissolving compared to the rate they are being formed.

Great, now we understand some of the physical, chemical and biological processes underlying the ocean acidification=doom argument. In order to determine the actual effect of increasing CO2 concentration in the atmosphere we have to look at the concentration of CO2 and temperature at 2 points in time as both are changing. For my example I decided to use the EPA’s stated 1.5C temperature increase since 1917 and an increase from 280ppm for my concentration. I used 10C as my current water temperature and 390ppm as my current CO2 concentration. Atmospheric pressure was assumed at 1atm. I also kept hearing a pre-industrial pH value of 8.2. This calculation is done under the assumption that preindustrial pH system was stable and thus increases from emissions will essentially add to the previously existing H+ concentration in the solution.

Our partial pressures for CO2 therefore turn out to be

PreI=397.14 Pa

Modern=553.234 Pa

The modified henry’s coefficient

KhPreI=18.205L*atm/mol

Khmodern=19.191LAtm/mol

Which means our concentrations for preindustrial and modern CO2 are given by equation 8.

C=P/Kh

And the values

PreI=2.153*10^-4 L/mol

Modern=2.845*10^-4 L/mol

Which gives us our H2CO3 concentration in both scenarios

PreI= 2.584*10^-7

Modern=1.476*10^-7

I only used the first dissociation constant as the concentration was already in the 10^-11 values so a 10^-22 values wouldn’t have been significant Leading to a total H ion concentration (from CO2) of

PreI= 6.46*10^-11

Modern=3.69*10^-11

OF course the net difference between these two values

Modern-Prei=2.075*10^-11 H+ ions in solution

So the change in pH is equal to -log(H+new+1*10^-8.2)

so roughly the total increase in carbon emissions has changed the pH to roughly 8.199

That’s not even measurable. In order to see the claimed pH increase the atmospheric increase in CO2 would have to be 100x greater than what has occurred. Surely we can say the acidity, a measure of h+ ions has increased 30% but that’s guaranteed from the chemistry and tells us nothing about the oceanic quality of life.

See to do that we would need to perform an experiment and actually collect data. Unlike global climate change these studies are comparably simple. Get a bucket and a CO2 tank add some corals and oysters and other carbonate loving critters and then set the atmospheric CO2 concentration above the water, find out what happens. Repeat the study for pre-industrial, modern double modern and prehistoric levels of CO2 simply add food and allow Ion exchange. In less than 5-10 years someone could conclusively prove CO2 is causing harm.

Even if you didn’t want to actually collect data there is one other scientific principle that the carbon controllers are violating. That’s the correspondence principal; we can look back at history and watch how CO2 trends match with carbonate critter fossil records. If we actually look back far enough to when CO2 was at its peak levels on this planet we find that most of our mollusks and carbonate dependent organisms evolved at the same time our atmospheric CO2 concentration was over 8,000ppm. Before anyone gets to claim that carbonate organisms are having problems they need to answer why they can’t deal with a CO2 increase of 30% while their ancestors thrived at concentrations higher than 200%. It just doesn’t make sense.

But what about that video?

She starts with 2 clear and noncontroversial statements and then 1 that is somewhat controversial, at least for me. Specifically that increased acidity makes it difficult for Calcium carbonate Ca(Co3-) dependent organisms to survive.

For her first demonstration she drops a block of dry ice into water and and we get to see some bromothymol blue change colors from blue to yellow. So yes she demonstrated that CO2 does make water more acidic. But she also clearly mentioned Atmospheric CO2 having an impact on ocean acidity. By dropping pure CO2 into the water it is essentially creating a system with 100% partial pressure at the liquid vapor interface. Essentially they are increasing the atmospheric CO2 by a factor of 3000.

The second demonstration was more of the same shenanigans. First they divvied up acetic acid vinegar, not carbonic into three concentrations; 1 with none, one with half and one with a concentration straight from the bottle. She then added some calcium carbonate, OOO fizzies. so yes the acid does react with the shell and outgasses CO2. No kidding, that has what to do with a carbonic acid/carbonate system? and that glazes over the fact that a CO2/carbonic acid system has a pKa value of about 6.3, acetic acid is closer to 4.8 it has both a substantially higher dissociation constant and does not form a carbonate complex. Essentially the demonstration showed nothing.

But then came the classic heartwarming moment. The swimming little critter in the oceans of tomorrow, heart wrenching I know. Except wait they took a thin walled shell with no critter and placed it in a solution of unknown composition, with a pH value expected in the oceans of the future, slowly the shell dissolved, really slowly, over several days the critters shell became transparent, oh how sad. For that whole time lapse they could have used two identical shells; one in modern seawater and the other in a tank with a controlled CO2 atmosphere. Instead they literally ch

ose the most meaningless way of demonstrating nothing, they didn’t use a chemically similar environment and they didn’t use actual organisms who regenerate their shell and that is fascinating.

So if you have made it this far and your head hasn’t exploded congratulations Here are some bullet points.

1. It is Interesting to note that we somehow have an accurate measurement of ocean acidity from 200 years ago when the apparatus to measure pH was only invented in 1924 and it wasn’t conceived as a measurement until 1909. It should be impossible to conclude within .1 pH unit the actual oceanic pH 200 years ago.

2. The maximum possible change from atmospheric CO2 pre industrial to today is less than .001 pH units, it is thus impossible to measure

3. Even if we could measure .001 pH units there are plenty of questions on the accuracy and calibration techniques associated with the measurement

3. It is impossible for CO2 to deplete carbonate ions in solution

4. Rivers and freshwater lakes are more susceptible to carbonic acid from atmospheric CO2, so why are we worried about the oceans?

5. It is essentially chemically and biologically impossible for carbonate dependent organisms to suffer from CO2 increases

6. Carbonic acid is not the same as hydrochloric or acetic acid.

7. pH from carbonic acid tells us nothing about the CO2/Carbonate system

8. There have been no experiments to demonstrate harm, only hypothesis and models.

9. The experimental framework for testing carbonate organisms with increasing CO2 is easy, yet unperformed

10. The organisms most susceptible to ocean acidification from CO2 evolved at a time when concentrations were 15 times higher than today.

11. Ocean acidification means nothing if the rate at which CaCO3 is being produced exceeds the rate at which carbonic acid consumes it.

12. The buffer capacity of the ocean is huge and incorporates carbonic acid, further demonstration of CO2 overwhelming this buffer is needed.