How Ocean Acidification may Result in Mass Extinctions

Global warming is widely understood by scientists, and to a lesser extent by non-scientists, as posing serious risks for future humanity.  As humans are land dwellers, it is perhaps understandable that more alarm has been generated by the projected negative impacts on land than in the ocean   Marine biologists, however, are now exploring the process of ocean acidification, another consequence of carbon dioxide emissions.  They are already seriously concerned that current trends could result in extinctions of oceanic species over the next hundred years.

 Climatology at present comprehends the observed rise in global temperatures as a consequence of human burning of fossil fuels, an activity which injects billions of tons of carbon dioxide annually into the global atmosphere. Political debate regarding the global warming process focuses on the twin concerns of rising temperatures and rising sea levels.  A substantial amount of the released carbon dioxide, as much as 50%, is absorbed by the world ocean. As carbon dioxide enters ocean waters, a chemical process takes place that generates carbonic acid. This process is gradually changing the acid balance of the world ocean. Over the past two hundred years, carbon levels in the oceans have risen sharply. Historically, ocean waters have been alkaline, having a pH of around 8.2. The pH of the oceans is now around 8.1 and dropping.  It is that pH levels will be around 7.9 by the year 2100. As pH levels get closer to the neutral level of 7.0, marine biologists expect that many ocean organisms will no longer be able to form shells out of dissolved calcium carbonate and will become extinct.  It is worth noting that the pH scale is logarithmic, so that the observed 0.1 increase in acidity actually represents more than a 25% increase! The current acidity rise in the oceans is therefore rapid and enormous, something not seen for millions of years. There are now a few blogs attempting to increase public awareness of the ocean acidification issue, for example here.

The list of ocean creatures that grow shells is very long. Clams, oysters, mussels, and scallops are dependent on the chemical process of creating hard shell from sea water. It is worth note that these species are economically valuable to the human race: world wide, millions of humans are economically dependent on shellfish. Biologists also believe that Phytoplankton, as well as Pteropods, tiny ocean snails that form the basis of much of the food web in some regions of the ocean, are dependent on dissolved calcium carbonate for their survival.  Most commercial fisheries in the ocean could collapse if these tiny food sources disappear.

One ocean species that is most imperiled by ocean acidification may be one that most humans are not familiar with: the coral polyp.  These relatively small creatures form the basis of the coral reef ecosystem, by building enormous structures of carbonate over thousands of years.  Coral reefs, however, are living structures. If the polyps organism should lose its ability to build new coral, it will die.  After that occurs, the reef eventually becomes a bleached structure that begins to erode, and soon stops hosting a large community of crustaceans and fish. Humans dependent on the coral reef for fishing, harvesting shellfish, or tourism activities such as snorkeling or scuba diving, are then deprived of a livelihood. Coral reefs around the planet are showing increasing signs of stress, and marine biologists suspect that coral may face extinction by 2100.

 It can be anticipated that ocean acidification will attract more political interest as time passes and as evidence accumulates of damage to the marine ecosystem. Ocean acidification, however, like other aspects of the global warming syndrome, is not a thing that can be instantly fixed. If the expected wave of extinctions begins as 2100 approaches, it will not be possible to suddenly solve the ocean acidification problem in time to prevent more extinctions.  One the world ocean becomes too acidic for the formation of calcium carbonate to be possible, it may take decades or even centuries to reverse the process by decreasing the amount of carbon in the atmosphere.