Tuesday, January 13, 2015

What Wallace did wrong

The climate-denier Twitterverse and blogosphere was all briefly excited in late December when a report was promulgated from CFACT about a supposedly “Climategate” level data problem with data on oceanic pH levels.  I took a look at the report, as I have had to understand this issue with regard to greenhouse gas impacts on Earth’s climate and how they relate to the energy industry.  Within seconds I realized that a major blunder had been committed by the author (a Michael Wallace) of the report.   This blunder is so basic that it is difficult to comprehend how someone who is purportedly educated in a scientific field could have made it.  However, it is understandable that someone with limited knowledge of basic oceanography (which is easily garnered in this Internet era of information) could make such an error.

What makes it worse is that the author, and then apparently several other persons, including some major climate change-skeptical media outlets, used this bogus report to malign the professional and personal integrity of government (NOAA) scientists who have made a career out of carefully and painstakingly making ocean pH and related ocean chemistry measurements to understand the how CO2 enters the oceans, the effects that it is causing, and what may happen in the future.  In this effort, the modern-day data is likely combined with modeling to project changes in future decades.  The model used was also maligned, and likely its motivation and method was misunderstood as well.

The blunder made by Mr. Wallace demonstrates a significant lack of understanding of basic physical and chemical oceanography.  In his pseudoscientific haste to demonstrate the supposed massive significance of his findings (noting that one-upping the established ‘experts’ on a major subject is a distinct hallmark of pseudoscience), Mr. Wallace did not first try to understand the system he was investigating. 

In order to explain the blunder, first you will permit me to explain basic oceanography.  If I state the blunder first without establishing context, many many people (particularly dubious skeptics and deniers) won’t try to understand the important context here.   And if you don’t understand the context, you won’t see how basic the blunder is when I reveal it.

(Note that in what follows, a click on any image will provide a larger image for easier perusal.)

To start, we begin with the ocean’s basic thermohaline (that’s temperature and salinity) circulation pattern.  Now, there are numerous cartoons such as the one I am displaying below, and yes, reality is much more complex.   There may be twists and turns and countercurrents and eddies that are important circulation features in the ocean, but which don’t matter here. This is the bare-bones basics.  But this is also basic enough that it does govern some of the basic physical and chemical characteristics of seawater at various depths in the ocean.  And that is very important in this discussion.

Figure 1

The salient point about this diagram is where the water starts, and where it goes.  Most deep water formation (the blue currents) occurs in the North Atlantic.    The water progresses southward, adds some deep water in the Southern Ocean, and then heads Pacific-ward, where it surfaces, and returns in warm currents through the Indonesian Throughflow and the Indian Ocean, and then the surface Atlantic, where it turns into eddies off South Africa and then the Gulf Stream.    That’s basically it.

Why this is important to ocean chemistry is the following:  as the deep water heads southward and Pacific-ward, there are two major carbon system changes happening.   Some CO2 was grabbed from the atmosphere as the water sank, which increases the total CO2 (henceforth TCO2).   The two main processes happening are the bacterial respiration of organic matter sinking down from the surface (which increases the TCO2), and the dissolution of calcium carbonate (CaCO3), which increases both the water mass total alkalinity (TA) and the water mass TCO2.  That may have been hard to follow, but this diagram (which was copied from this very good lecture, http://www.soest.hawaii.edu/oceanography/courses/OCN623/Spring2012/CO2pH.pdf ) should make it clear.    Note primarily the difference between the main water mass types shown here, particularly the difference between the warm surface and the deep Pacific.

Figure 2

Now I’m going to discuss the carbonate system, briefly.    The alkalinity is primarily composed of bicarbonate and carbonate ions, HCO3- and CO3(2-), respectively.  There’s a little bit of other stuff, like borate, but not much.   The saturation state of seawater with respect to CaCO3 is simply the product of the concentrations of calcium ion (essentially constant) and carbonate ion, compared to the solubility constant of CaCO3.   There are actually two of them, because there are two major forms of CaCO3, calcite and aragonite, and aragonite is slightly more soluble in seawater than calcite.   The saturation state of seawater varies due to the concentration of these ions, and also varies with temperature and pressure a little.    The net result of this is that the saturation state of deeper waters is lower than surface waters, and because of those deep water mass chemical changes, the saturation state in the Pacific is lower than in the Atlantic.   There are a couple of different terms to know – the lysocline is where the effects of dissolution can be seen in the sediments, the carbonate compensation depth (CCD) is the depth at which the addition rate of carbonate to the sediments matches the rate of dissolution, and the saturation horizon (or saturation depth) is the depth at which the water column goes from supersaturated to undersaturated.


Figure 3

Figure 4

Hearken back to the second figure.  The much shallower aragonite and calcite saturation depths in the Pacific are directly related to the water mass carbon/carbonate system evolution that occurs as the water follows the general THC pattern. 

So now we turn to pH.   The respiration and CaCO3 dissolution processes don’t affect the pH, but adding CO2 to the oceans does.   As shown here:

Figure 5

The addition of CO2 makes carbonic acid, which is not very stable, so it dissociates into H+ and HCO3- (bicarbonate ion).    That has the effect of lowering the pH, of course (pH being the negative logarithm of the hydrogen ion concentration), which is the process of acidification.  I’m not going to get involved in the linguistic semantics of acidification in alkaline seawater:  if the pH is going down, that’s acidification.    Now, there’s two aspects of this.   Adding CO2 decreases the pH, and it also shifts the equilibrium between carbonate and bicarbonate toward bicarbonate ion (which incidentally rather drastically shifts the carbonate saturation state toward undersaturation).   See that all here:

Figure 6

Thus, even a small shift downward in pH can make a major change in CO3(2-) concentrations, and concomitantly a major change in the carbonate saturation state.   THIS IS A FACTOR OFTEN UNDERPLAYED BY CLIMATE CHANGE SKEPTICS, I must note.

So now after all that it is time to get to the major Wallace blunder.   Here is the figure of note:

Figure 7

According to the legend (where I assume WDO = WOD), the X’s are for average annual pH for <= 200 meters.    The green circle data point are “stated in a reference” (where, by whom, is not stated).   But the blunder is right before us:   the pH values are all for  waters less than 200 meters depth.  I.e., the surface.

Here are the problems with that.   #1, as shown earlier, the water masses at the surface are not those with a carbonate system that is most susceptible to acidification.   #2, the pH of the water column decreases with depth.  #3, because pH is logarithmic, values of pH at the surface, in the 8.1 – 8.3 range, mean that OH- concentrations are 5- 10 times higher than for pH values at depth, in the 7.5 – 7.8 pH range.   That means it is going to take a much larger addition of H+ (caused by the addition of CO2, Figure 5) to change the pH at the surface than to change it at depth.   

Wallace questioned the report from Sabine and Feely which contained a schematic diagram of ocean pH change from 1850 to 2100.   This model-generated figure displays curves of pH change which are obviously not natural – they can only result from averaging over the entire ocean surface waters.    The ocean circulation patterns shown in Figure 1 tell us that lower pH deep waters will come to the surface in the Pacific, where they will be susceptible to further acidification by the absorption of atmospheric CO2.  And in areas where CO2 is actively being absorbed, there have been direct and calculated pH decreases and changes in the carbonate saturation horizons.  Here’s where the CO2 is entering the oceans, and where the carbonate saturation horizons have been changing. 

Figure 8

(Note that you don’t have to measure pH directly, as much of the discussion on Wallace’s work focused on .   Because the system is overdetermined, if you measure just two of the following:  TCO2, pH, pCO2, or carbonate alkalinity (CA), you can calculate the other two.  Because it is now possible to measure pCO2 and TCO2 to high accuracy, the measured pH can be compared to the calculated pH, and back-compared to both where and when pH wasn’t measured, but where TCO2 and pCO2 were measured.)

All of which has happened around Hawaii.  Furthermore, glass electrodes have been replaced by much more accurate methods of pH determination, such that the actual changes can be measured.
So what has been seen around Hawaii?  This:

Figure 9

which shows a greater change between 235-265 meters than 0-30 meters, as expected.  Note that measurements (orange) agree with calculations (green), over a 20-year period. 
Here’s another way to look at the Hawaii data, showing the variation of pH with depth, and showing the variation of the rate of change of pH with depth. 

Figure 10

So the greatest rate of change is at about 300 meters – where ocean chemistry and oceanography tell us it would be, and below the depth of the measurements in Wallace’s prize figure (Figure 7).   Wallace’s figure is suspect in other ways, because there is an obvious decline from the high values shown in the 60s through the 80s and following.   Since we don’t know where the measurements are taken, we can’t read much into this, but without the earlier values in the chart, there would likely be a declining trend paralleling the model curve (or steeper) starting in the 1960s or so.

So Wallace’s blunder is to solely show surface (less than 200 meter) pH values without any indication where or how they were taken or how many were taken per year.  Notably most of the early values were likely taken from ships in specific cruise tracks or regions.  Oversampling in high pH regions and undersampling in low pH regions will undermine any possibility of detecting a trend.   Thus, very little value can be given to the data comparison in Figure 7.

Except:   one of the things that Wallace did was to highlight the model results.   The red line in figure 7 is taken from a NOAA publication, with the figure below (Figure 11).  

Figure 11

I did a little bit of work with this figure, to  try and estimate what it tells us about the periods covered in the Wallace figure (Figure 7) and also the Hawaii data.  So here’s my modified figure.

Figure 12

Looking at this figure, it can be estimated that the pH change from 1910 to 1960 is about 0.03 – which is not very much, especially with the level of technology in this period. Given that we don’t have any single station data in Wallace’s figure, any real pH change can’t be estimated from it.  But if we then look at the interval 1990-2008, which is the period covered by the Hawaii data, because the curve has steepened I estimate that the change in the model is again about 0.03.  And if we look at the Hawaii data, the change appears to be about 0.03 in the 0-30m surface data (I think about 8.11 to 8.08) and about 0.06 in the 235-265m data (8.07 to 8.01?).   So the match between the Hawaii data rate of pH change – actually observed and measured accurately – with the model that was disputed actually turns out to look pretty good.

So is there any worth to the data prior to the 1980s?  Absolutely – to establish a baseline, as accurately as possible.  But clearly as CO2 concentrations in the atmosphere have been increasing, the rate of absorption by surface waters is increasing, and the rate of pH change is expected to be increasing.  The model indicates that there is not much pH change expected in the period prior to the 1960s – which is exactly what the available observational data in Figure 7 indicate, not much change, i.e., hardly any measurable change.  So are the data needed for the model?   It looks unlikely that they show anything other than the very slow rate of change indicated by the model, and in that they are useful for verification.  But for insight into the changes wrought by CO2 absorption, more modern data needs to be consulted, and when that is done, the declining trend in pH predicted by the model is borne out by the observational data.

A final point:  as I noted above, the effect of pH change on the carbonate saturation state does not appear much in the skeptical mentions of ocean acidification.  But this is actually the crucial aspect of the issue.  A small decrease in seawater pH means a big change in carbonate saturation state.  (Remind yourself of Figure 6 again.)  In deeper waters, it means that organisms with shells made of calcite or aragonite will be more prone to dissolve (and damage due to dissolution has been noted on living pteropods*, whose shells are made of aragonite).  For shallow waters, even if the water is supersaturated, ocean acidification means that it will be less saturated, and that means in general that calcifying organisms like corals have to work harder to make their CaCO3 skeletons.   That’s the peril to the reefs from ocean acidification that has been noted in several studies. (And also, recently, it was found to be what imperils baby oysters.)

* Could have implications for Arctic ecosystems, as some of them are major foodstuffs for fish like pollock.

Given all that I’ve discussed, I also suspect that Sabine’s comments to Wallace about Wallace’s work were not so much a threat as an observation.  Anything this ill-founded will likely be treated with the respect it deserves in the oceanographic community, and if that is where Wallace would like to make a career, this wouldn’t be very helpful in that regard. 

Because oceanographic scientists know what they are doing and are confident in their knowledge, I doubt that what Wallace did (and what was spread around liberally to fertilize skeptical discontent) will have little impact on the science being practiced by legitimate oceanographers.  But it would be useful if some clarifications were issued by these sources to whit:  there isn’t much in what Wallace did, and what CFACT promoted, to call into question the current understanding and study of ocean acidification.  A polite retraction would be in order here.  I won’t hold my breath (besides, that would mean too much CO2 in my lungs, because of my own personal respiration processes).

I would be remiss if I did not point out that other commentators have also addressed Wallace's work - and all have pretty much reached the same conclusion, even if different aspects of it were discussed.  Furthermore, in the Comments section of the CFACT article linked in the previous paragraph, some of Wallace's shortcomings are taken to task as well. Given the cumulative comprehensive nature of these examinations, the overall evaluation of it results in a substantial level of negative agreement.  Meaning that it isn't very good at all.

 Here are some:

Not pHraud but pHoolishness

Annals of Derp: global whacking

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