Ocean Acidification

By Roger Payne

By now, most people probably know that the carbon dioxide (CO₂) that is generated by burning fossil fuels causes global warming. But fewer people know that the CO₂ the seas absorb combines with seawater to make carbonic acid, which raises the acidity of the oceans. Since humanity started burning coal in earnest 150-200 years ago the seas have become 30 percent more acidic and it is now known that in some areas such species as oysters, and corals are already being prevented from retaining (or forming) their shells, simply because these animals can’t make their shells or their stone-like houses if the water is too acidic.

Ocean acidity also devastates a series of tiny animals with unfamiliar names like pteropods—a kind of snail with wings that are used to fly underwater. Pteropods form shoals containing millions of individuals and are a principal food for baleen whales.

Ocean acidity already affects such tiny planktonic organisms as coccolithophores, corraline algae and foraminiferans, all of which live at the bases of ocean food chains. If the seas get acidic enough to cause these plankton populations to crash, it will demolish the complex food pyramids that support all economically important ocean food pyramids. That’s because all such food pyramids are entirely dependent on plankton. If the plankton die, the whole pyramid dies. No phyto-plankton, no zooplankton. No zooplankton, no fish. No fish, no whales (or seals, or sea birds, or the roughly1billion people-who-depend-on-fish as their primary source of animal protein). We must also not forget that it is plankton that provide the oxygen for two out of every three breaths we take (a topic I will have more to say about later).

Scientists now predict that people must either plant billions of trees to convert the excess CO₂ into wood or stop producing so much carbon dioxide. If we don’t do either, ocean acidity will more than double in the next 40 years.

But how bad could that be?

Well, in the last 20 million years ocean acidity has never changed at a rate any faster than 1/100th of that rate. Life has no mechanisms to cope with such rates of change.
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One of the benefits of the 21st session of The Conference of The Parties (COP) currently taking place in Paris is that several independent organizations seem to be starting to consolidate their efforts—a step that seems bound to give them greater impact. Of particular promise is the recently announced Tapestry of Hope, representing 1700 local service projects that combine Jane Goodall’s powerful Roots and Shoots programs (now operating in more than 130 countries) with Sylvia Earle’s Mission Blue (which specifies 46 Hope Spots—each being an area critical to ocean health).

When Drs. Goodall and Earle announced this important initiative Sylvia Earle noticed that the agreement the COP was discussing failed even to mention ocean acidification—a rather strange omission, I thought, given that ocean acidification may just be a more immediate and all-encompassing threat to life on earth than global warming is, simply because it may reach lethal levels sooner (it is already high enough so that such key species as corraline algae, staghorn coral, pteropods and oysters are unable in some areas to get carbonate ions to precipitate out of solution and that means they cannot form their shells or coral skeletons that they need to protect and enable their lives.

It is clear enough that life on land will take a terrible hit from global warming, but thousands of species will nevertheless probably survive by moving to higher ground or expanding their ranges into the polar seas where the water can be counted on to remain cool, even when the oceans warm overall, simply because polar waters will continue to lose heat during the dark months of winter.

The acidity of the seas, on the other hand, will inexorably increase over time, worldwide. This means that neither the polar oceans nor any other part of the seas will represent a Coventry where the levels of acidification can be counted on to remain low enough for life to persist.

All in all, the massive increase in CO₂ from burning fossil fuels produces two quite separate effects on ocean life. But the time it takes for the oceans to become dangerously acidic seems to be shorter than the time it takes them to become dangerously warm. In general, seriously consequential acidity appears to take decades while seriously consequential warming appears to take much longer before it exerts a comparably destructive effect on ocean life.

In each case these rates depend on the intensities at which different species are affected—a subject about which there is very little information. However the fact remains that the time it takes for heating to affect species negatively may be significantly longer than the time it takes to see similar damage from acidification.

But the key point here is that although both are triggered by increasing CO₂, warming and acidification are very different processes and it would be naive to assume that the rates at which their effects will cause problems for ocean life should be the same. They can be expected to affect different species and different ecosystems after different delays and therefore should be considered separately.

In summary: I believe that the most imminent threat we face may very well not be global warming but the acidification of the oceans, simply because acidification seems to be causing serious mischief to ocean life sooner.

If that it turns out to be true I would not be surprised if the most serious problem our species now faces is ocean acidification, not global warming.

© Roger Payne
Dec 9, 2015
Dr. Roger Payne is the Founder and President of Ocean Alliance.