Sunday, 6 May 2018

Ocean acidification myth

pH is a measure of acidity (or basicity). When pH is below 7 solutions (like the oceans) are said to be acidic. With pH above 7 they are basic. Ocean pH is about 8, basic. It actually varies quite a lot depending on which ocean you measure, at what depth.

Climate alarmists claim CO2 from fossil fuel combustion is acidifying oceans, because it makes "carbonic acid".

NOAA claim:

"In the past 200 years alone, ocean water has become 30 percent more acidic"
due to CO2 from burning fossil fuel.

National Geographic claim:

"Over the past 300 million years, ocean pH has been slightly basic, averaging about 8.2. Today, it is around 8.1, a drop of 0.1 pH units, representing a 25-percent increase in acidity over the past two centuries."

Let me examine NOAA's claim:

1) There is 38,000 Gt on carbon dissolved in oceans (27ppm). Mostly as the bicarbonate ion HCO3- Total carbon available in fossil fuel reserves = 5,000 Gt. If all that fossil fuel burnt, and the CO2 produced then dissolved in the oceans it will raise the ocean carbon content to 31ppm. To put things into perspective: in contrast to the 27ppm of carbon, oceans have 35,000ppm of salt in them.

Total carbon emissions (as CO2) since before industrial times ~ 500 Gt. Not all that can end up in oceans. Some stays in atmosphere, some is sequestered on land (in plants and trees), more is sequestered by oceans.

2) When carbon dioxide dissolves in water. It first becomes CO2(aq). Then:

CO2(aq) + H2O(aq) ⇌ H2CO3(aq) ... (A)

H2CO3(aq) is "carbonic acid".

But when this happens only 0.3% of the CO2 dissolving in the oceans becomes "carbonic acid". The rest mostly stays as CO2(aq).

Note: For the 0.3% claim see: "Carbon Dioxide, Dissolved (Ocean)" by Zeebe & Wolf

3) When this "carbonic acid" is made it is a very weak acid. With a Ka = 4.2E-04 (Ka = dissociation constant). This is the dissociation of H2CO3(aq) to make acid:

H2CO3(aq) + H2O ⇌ H3O+(aq) + HCO3-(aq) ... (B)

The actual (active) acid here is H3O+(aq), sometimes written as H+(aq), and referred to as "hydrogen ions", or hydrated hydrogen ions. This is what pH measures. pH is literally "the negative log of the hydrogen ion concentration".

Such a low dissociation constant implies about 0.5% of the carbonic acid (H2CO3) will act as acid (as hydrogen ions). [calculated as the square root of Ka a by a "very back of envelope" method!].

So 0.5% of 0.3% of 500Gt is how much actual acid could have been made. Insignificant.

Note: In comparison a strong acid like hydrochloric acid is almost 100% dissociated to make actual "acid", or hydrogen ions, which may be written H+(aq) or H3O+(aq).

4) Carbon dioxide dissolving in oceans acts as a buffer, not an acid. As the name implies, a buffer prevents, or greatly reduces, pH changes.

5) What kind of pH change might we really expect?

I will do "very back of the envelope" calculations here. If I make a mistake, please laugh at me. Then correct me.

Assuming the pH of oceans = 8.1, as National Geographic claim, lets do the back of envelope calculations to figure out how much pH may have fallen in the last 200 years.

The mass of oceans is usually given = 1.4E24 grams. How much acid is that?

A pH = 8.1 says that the [H3O++] = 10-8.1 = 7.9433E-09.

Multiply the two. Grams of H+ = 1E16 grams (very approximate!). A lot of hydrogen ions, but then, our oceans are very big.

How many hydrogen ions may we expect from 500Gt of carbon (dissolving as CO2)? The Atomic Mass of C = 12. 500Gt of carbon = 500 × 1000,000,000 t = 500 × 1000,000,000,000,000 g = 50E16 g of Carbon = 50/12 × 1016 moles, or 4E+16.

4E+16 × 0.3% × 0.5% = 6E+11 hydrogen ions. The ratio of hydrogen ions added is 18600:1 We increased the acidity from 18600 to 18601. Big deal! By adding all that CO2 we made the oceans more acidic by 1 extra hydrogen ion in 18600. An addition of 0.0054%, not 30% as NOAA said. The pH change we may expect to actually get is too small to measure. It will be within the error bounds of any measurement we make. We won't be able to distinguish it from signal noise.

The claimed pH change from 8.2 to 8.1 as NOAA and National Geographic claim is a 26% change in acidity (remember pH is a logarithmic scale). The actual change must be less than 0.0054%. They exaggerate by over 3 orders of magnitude. By 26% ÷ 0.0054% = 4819. National Geographic by 4819 times. NOAA by 5560 times.

6) Evidence suggests fraud in the "science" as well.

The pH data has been tampered in the CO2-AGW consensus paper on declaring ocean water acid by 0.1 decrease. The reanalysis of public pH data from the same source in Univ of Hawaii shows the data tampering in the peer-reviewed consensus paper.

Note: The pH standard deviation range = 0.19 - 0.28.

Note: Ocean acidification of the North Pacific Ocean (pdf), by Richard A. Feely, Victoria J. Fabry and John M. Guinotte

7) A reply from a critic

There is at least one attempt to refute me here: Bad Science or "Climate Alarmism". You tell me

Summary:

  1. The relative change in the carbon content of oceans in the last 200 years is small.
  2. Only 0.3% of carbon dioxide dissolving in oceans becomes carbonic acid.
  3. This carbonic acid is a weak acid, with 0.5% of it dissociating to actual acid (hydrogen ions).
  4. CO2 in sea water acts as a buffer. To prevent changes in pH (acidity)
  5. NOAA exaggerate the change in likely pH 5560 times over.
  6. Reanalysis of the scientific paper claiming oceans have become more acidic by 0.1 pH shows the paper cannot be trusted.

This is the best reply I've had so far.


chiralSPO, Global Moderator, Naked Science Forum King!

Ocean pH is due to only one thing [H+]. Yes, there are many other ions in solution, each of which might play a role in determining [H+], though not as many as you seem to be indicating (it doesn't matter how much salt there is: Na+, K+, Cl, and Br will have NO effect on pH in the range of plausible pH values, as the pKa values of Cl, and Br are < 0).

There is a complex "buffer" related to concentrations of CO2, HCO3, CO32–, H2PO4, HPO42–, B(OH)3, B(OH)42–, Mg2+, Ca2+, etc.

As you say in your blog:
Quote
I will do "very back of the envelope" calculations here. If I make a mistake, please laugh at me. Then correct me.
I will skip the first step, and focus on the second:

Quote
Assuming the pH of oceans = 8.1, as National Geographic claim, lets do the back of envelope calculations to figure out how much pH may have fallen in the last 200 years.

The mass of oceans is usually given = 1.4E24 grams. How much acid is that?

A pH = 8.1 says that the [H3O++] = 10-8.1 = 7.9433E-09.

Multiply the two. Grams of H+ = 1E16 grams (very approximate!). A lot of hydrogen ions, but then, our oceans are very big.

How many hydrogen ions may we expect from 500Gt of carbon (dissolving as CO2)? The Atomic Mass of C = 12. 500Gt of carbon = 500 × 1000,000,000 t = 500 × 1000,000,000,000,000 g = 50E16 g of Carbon = 50/12 × 1016 moles, or 4E+16.

4E+16 × 0.3% × 0.5% = 6E+11 hydrogen ions. The ratio of hydrogen ions added is 18600:1 We increased the acidity from 18600 to 18601. Big deal! By adding all that CO2 we made the oceans more acidic by 1 extra hydrogen ion in 18600. An addition of 0.0054%, not 30% as NOAA said.

The above approach is fundamentally flawed (I have stricken the primary mistake through). As you point out, the system is buffered, by the equilibrium of H+ CO2, H2CO3, HCO3, and CO32–. This complex buffering means that the linear relationship assumed in the above calculation is not valid. Instead, we need to consider the relationship between all of the species. You have also not considered how much of each of the carbon-related species are already in solution, and what their relationships are to each other and to pH.

I recommend studying up on this more before posting:

https://en.wikipedia.org/wiki/Bicarbonate_buffer_system#Henderson%E2%80%93Hasselbalch_equation
http://www.atmos.umd.edu/~russ/620_04OceanChem.pptx (downloadable lecture slides)

It is also worth emphasizing (and you have noted it, but I think you should consider the ramifications more carefully), that the system is NOT IN EQUILIBRIUM. The pH is not the same everywhere because the ocean is not mixed perfectly well. This means that at the very surface, where the ocean is in contact with the acidifying CO2, the buffer can be temporarily over-burdened, before more bicarbonate comes up from the depths to restore equilibrium. This is bad news for marine life in shallow waters (read: everything you can see while snorkeling), which is damaged by the imbalance, even if it is temporary.

Essentially, the calcium carbonate in the marine organisms serves as the base in the equilibrium.

3 comments:

  1. ocean ph varies significantly with depth, and the surface is the most acidic

    https://socratic.org/questions/how-does-ph-change-with-depth

    This massively changes all the numbers used in your calculations.

    ReplyDelete
    Replies
    1. NOAA claimed "oceans are 30% more acidic". They did not say "only the top surface of oceans are 30% more acidic". The purpose of the post is to refute NOAA, not to find a pH for oceans.

      It does not massively change my calculations nor numbers. I'm still waiting for someone to show me an error there. Still waiting for an attempt at a refutation.

      Delete
  2. A reduction in alkalinity does not acidification make...When the ph drops below 7.0 , that is acidification...When the ph reduces from 8.2 to 8.1 ,, that is a reduction in alkalinity........Over the laST 4 years, I have measured ocean ph , north of the Canadian Arctic Circle,, the Equator ( Galapagos Is.),, and the Antarctic Peninsula,, and it was never below 7.8 ph ......

    ReplyDelete