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.
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.
Diagram:
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
Here are some:
Not pHraud but pHoolishness
Annals of Derp: global whacking
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