Tag Archives: Ocean acidification

Oceans on acid

Last Monday I have read an article in a news paper that caught my eye. It was somewhat hidden in a corner at the last page and was about the acidification of the Northern Sea. When checking I found that the article probably originated from Reuters. It was all about a report by 60 experts for the Arctic Monitoring and Assessment Programme, commissioned by the eight nations with Arctic territories.

There is a lot to be said about this short article, but so little time. I will focus on the alarmist message and how it is communicated.

To begin with, a strong statement from that article (my bold)

The report said the average acidity of surface ocean waters worldwide was now about 30 percent higher than at the start of the Industrial Revolution

I heard that claim many times before, so I knew what it was about. A “30% increase” seems a lot, but take in mind that the pH scale (that we commonly use to determine acidity) is logarithmic and 30% converted to a logarithmic scale is not exactly what one would expect.
The pH scale measures how acidic or how basic a solution is. It goes from 0 (very acidic) to 14 (very basic) over 7 (neutral). But as said, the scale is not linear, it is logarithmic. A solution with a pH of 4 is ten times more acidic than a solution with a pH of 5 and hundred times more acidic than one with a pH of 6. The same the other way round. A solution with a pH of 10 is ten times more basic than a solution with a pH of 9 and hundred times more basic than one of pH 8.

pH scale

pH scale

It is strange that in the article this is expressed in a measure that will be difficult the apprehend by a layman. How many laypersons would have a correct understanding when they been told of a 30% increase in acidity? They would probably be horrified because we are more used to the logarithmic scale.

The article stated that the average acidity (technically, the concentration of the H+-ions in seawater) is 30% more than in the past. So let’s see what this means converted to a pH-value. The pH-value is the negative log of the concentration of H+-ions in a solution.
Historically, the average pH value of the oceans was around 8.2. My knowledge of chemistry is a bit rusty after so many years, but this is how I think it goes:

  1. A pH of 8.2 means: 1×10-8.2 M H+-ions. Or in a more workable form: 6.3×10-9 M (or 0.0000000063 M)
  2. Add 30 percent to that: 0.0000000063 M x 1.3 = 0.0000000082 M
  3. The final pH after increasing it with 30% will be: -log(0.0000000082) ≈ 8.1 (which is the current average pH of seawater)

Coming from 8.2, this leaves us with a pH decrease of about 0.1 over more than a century, which isn’t that impressive at all. The statement about the 30% acidity increase seems to be made especially for impact.

Another thing that strikes me with this kind of releases: not only is the explanation of the acidity rather misleading, the same can be said about the terminology, for example the term ocean acidification. Ocean water has a pH of about 8.1, the arctic water seemingly somewhat less. That is not acidic at all, it is slightly basic. But does it not get more acid? Technically it is possible to say that, but it is closer to the truth to say that the seawater gets slightly less basic or going somewhat more towards neutral. Saying that going from 8.2 to 8.1 or from 8.1 to 7.8 is getting more acidic is rather misleading. Even when the pH drops 0.3 units it is still not acidic. If we take the scenario from the Multi-Ecosystem Comparison-paper (0.0017 pH units per year), it would take about 650 year before getting to neutral. After that it would start to get acidic, assuming we succeed in putting CO2 in the air for the next 650 years.

Then there is of course the mandatory assumed attribution (but look at the experts-statement, the consensus seems to been cracking a bit…):

At almost 400 parts per million (ppm), there is now 40 percent more carbon dioxide in the atmosphere than before the industrial era began. Almost all experts say the rise is linked to the burning of fossil fuels.

This I found an very odd statement:

“Ocean acidification is likely to affect the abundance, productivity and distribution of marine species, but the magnitude and direction of change are uncertain.”

So there is the possibility it doesn’t effect abundance, productivity and distribution and even if it does, no statements can be made about how much or in what direction? I can be wrong, but this looks to me: we don’t know squat.

And finally, look at the end of the article:

The report will be presented to Arctic governments at a meeting in Sweden next week attended by U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov, among others.

The article has probably more to do with politics than with science.