Ocean acidification - are they sure it's CO2 to blame?

Factual Questions
1

I’ve just read this BBC article on ocean acidification. Very interesting, and quite alarming. But why are they so sure it’s CO2 to blame? Sure, more CO2 appears to be being dissolved, but what about other pollutants like SO2 which dissolves to form Sulphuric Acid? The tests being conducted mentioned in the article seem to be concentrating on CO2 to the exclusion of all else.

Can someone point me to an article which deals with this?

2

Yes, it’s specifically because of CO2, which forms carbonic acid when dissolved in water. Off the top of my head, I’m not sure if the researchers measure carbonic acid directly any more, since the equilibrium equations are very well understood. Given the CO2 concentration and pH, you can calculate the carbonic acid concentration with a lot of precision. Wiki good details on the chemistry. Also, here’s another good article that deals with the chemistry, and specific effects on the ocean.

3

I’m not disputing that more CO2 is being dissolved in the oceans: I’m asking if they’re sure it’s to blame for the significantly increased acidification because there are plenty of other pollutants which might be to blame. And I’m asking if they’re testing for it. Just because CO2 is the probable cause doesn’t mean it’s the actual cause.

4

Here’s a Royal Society paper on the topic http://royalsociety.org/displaypagedoc.asp?id=13539 [PDF file] . Section 2.2.2 basically shows that the increase in CO2 in the ocean translates to an increase in H2CO3, ie carbonic acid. So there’s no doubt that some of the acidification of the oceans is due to CO2. While I can’t immediately find a direct statement that this accounts for all or nearly the PH change observed, there is no other plausible mechanism; SO2 pollution for instance is stable or decreasing, as the reduced incidence of acid rain damage to forests shows.

5

But a given amount of CO2 dissolved in water will increase the acidity by an amount you can calculate. If you observe that CO2 concentration goes up, you can predict how much the pH will change. In this case, the prediction is consistent with the change in pH.
Here’s a nice graph of such predictions (from this somewhat related discussion). Looking up the numbers, CO2 has increased from about 250 ppm to 350 ppm over the last century. On that graph, that’s consistent with a decrease in pH of .1, which we’ve also observed.

As scientific evidence goes, that’s just about as good as it gets.

6

Thank you. Precisely what I was seeking.