Ocean acidification: cooler or not, reason to take CO2 seriously

One thing that does appear likely to do well with increased CO2 is sea grass. While dugong will presumably welcome the news, it's hard to see how substituting reefs with beds of sea grass is going to be a good deal for ocean productivity overall.

As to the effect on plankton, the picture is admittedly unclear. Coccolithophores, important single celled algae that build a shell of calcite plates, were believed from initial lab studies to suffer stress and deformity under increased acidity. (This is mentioned in some of the Australian articles listed above.) But, early in 2008, a surprising new study with a different experimental set-up indicated that a few species actually did better under increased CO2. Before "anti-alarmists" claim this as a victory, there seems to be some scepticism amongst scientists about the results and their implications, and further studies are bound to be under way.

If coccolithophores really do respond by continuing to get heavier, this could work as an increased CO2 sink, at least if their population does not drop. However, there are also the uncertainties as to whether it might displace other useful phytoplankton, and how its predators will respond. (Do they like or dislike eating heavier coccolithophores?) It would seem that one would have to be a strong optimist to believe that all future research will be positive, and that heavier coccolithophores alone will unexpectedly save the planet. It is also likely to take many years to be certain as to what is going on.

Which brings us to the real disaster scenarios. The earth has undergone intermittent major extinctions on both land and the oceans, and the length of time over which they have taken place indicate that you can’t blame them solely on asteroid hits or extreme vulcanism.  Here are two suggested contributory mechanisms related to CO2 that should give concern:

• if the oceans lack enough oxygen, anoxic bacteria may make huge quantities of poisonous hydrogen sulphide gas, which could kill on both land and in the sea.  According to this article, the estimated quantity of atmospheric CO2 at the time of the last two big extinctions was just below 1,000ppm, a level which the earth may need only a century or so to reach. (If the ocean's carbon sinks collapses significantly due to increased acidity, it may be reached even faster than the current IPPC projections expect.);
• very recently, Scott Wooldridge, a researcher from the Australian Institute of Marine Sciences, has put forward a "unifying hypothesis for mass extinctions" that increased ocean acidity may, at specific levels, interfere with the operation of an important enzyme called urease.  The effect of increasing acidification may therefore not be uniform, but have particular "dead zones" which interfere with life. The first such zone is reached when ocean pH reaches 7.9, which can be expected with atmospheric CO2 of 560ppm: a level easily reached within 50 years. This theory is novel and (according to its author) useful in explaining some unusual features of past mass extinctions. It certainly warrants serious investigation, as it suggests that something akin to another extinction event is within ready reach unless urgent action is taken on CO2 emissions.

It is clear from reading the material that there are many, many scientists who are very concerned about the fate of the oceans. It seems a common feeling that the IPCC process has badly underestimated the importance of the fate of the oceans when considering climate change.

What's more, there seems to be very little in the way of convincing reasons being offered against taking it seriously. Bob Carter is a marine geologist and enviromental scientist, and has certainly been published in these fields. I stand to be corrected, but so far I have not found anything in which he has set out any detailed grounds to dismiss concerns about ocean acidification. He did claim at On Line Opinion that the Royal Society's estimate of future pH decline by 0.5 units is "known to be exaggerated by a factor of about 3," but did not cite the basis for that claim.

It seems that the most sceptics can credibly argue is that we should wait until the consequences of acidification are fully understood. There are, it is true, possible "winners and losers," but the likely losers appear to be things we should really value. With CO2 currently at 380ppm and rising at a couple of percent per year, just how helpful will it be to wait 20 years if it proves that reefs are indeed about to collapse, there is nothing much to replace the pteropods in the food chain, not all plankton like increased acidity, and even the humble mussel and oyster will not be easy to grow? All of these dangers exist even if current global temperatures completely flat-line.

Furthermore, if the serious danger level for mass extinction-like events in the oceans is around 560 to 900ppm of CO2, there is absolutely no time to waste.

In the absence of better arguments from the sceptics, or an implicit optimism that Nature will look after us (an attitude usually more attributed to Greenies rather than warming sceptics), it's very difficult to avoid the conclusion that ocean acidification is indeed reason enough for the world to just get on with working out effective ways to dramatically reduce future CO2 emissions.