By Paul Roth FRACGP
Ocean acidification has been called “the other CO2 problem” and even “global warming’s evil twin”. It occurs when carbon dioxide dissolves in seawater, producing carbonic acid (H2CO3).
Carbonic acid rapidly dissociates to produce hydrogen (H+) and bicarbonate ions (HCO3-). The hydrogen ions so produced combine with carbonate ions (CO3), sourced from calcium carbonate (CaCO3) to form more bicarbonate. This reduces the amount of available calcium carbonate.
Ocean acidification must be recognized for what it is – A global challenge of unprecedented scale and importance that requires immediate action to halt the trend of increasing acidification (EPOCA 2009).
Calcium carbonate is used by many marine organisms (including coral, oysters, mussels and many types of plankton) to form shells and skeletons. Less calcium carbonate makes it harder for these organisms to precipitate calcium.
As the oceans have absorbed about one-third of all anthropogenic carbon dioxide, they are now 30% more acidic than in pre-industrial times. This drop in pH is already reducing calcification rates of some marine calcifiers, especially those in colder waters (which can absorb more CO2 than warmer seawater).
If CO2 emissions continue on their current trajectory, oceans will be 3 – 5x more acidic than pre-industrial levels by 2100. This will be more acidic than at any time in the last 300 million years. The effects of this are unprecedented, but likely to be overwhelmingly negative – major impacts that will probably ramify upwards through marine food chains to apex predators.
Ocean acidification could trigger a chain reaction of impacts through the marine food web, beginning with larval fish and shellfish, which are particularly vulnerable (EPOCA 2009)
Coral reefs will be placed under increasing threat as acidification progresses. If present emission rates continue it is thought that they will start to dissolve (ie calcium carbonate will be reabsorbed into solution) by 2050.
Because of major inertia in the system, the acidification process is essentially irreversible over any time frame meaningful to us (ie > 10,000 years). Likewise, even if we were to stop all CO2 emissions tomorrow, ocean pH would continue to drop for some time (at least decades) as it reached a new carbon equilibrium with the atmosphere.
Because acidification is independent of carbon dioxide’s effect as a greenhouse gas, geo-engineering strategies that aim to cool the planet without removing atmospheric CO2 will have no effect on ocean acidification. Approaches to offset acidification (such as the application of crushed limestone to the oceans) would need to be at such massive scales that they would be prohibitively expensive (both economically and environmentally). The only solution to this problem is to stop emitting carbon dioxide.
Acidification will have impacts on key Australian marine ecosystems such as those of the Southern Ocean, marine protected areas on the southern margins of the Australian continent (the Great Australian Bight and Tasmanian seamounts) and, eventually the Great Barrier Reef (ACE-CRC 2008)
Now take action.
We don’t have long to turn things around. Ocean acidification is already making the calcified parts of some sea creatures thinner and lighter. Coral reefs are going to start disappearing by 2050 at the latest. This is starting to happen right now, independent of global warming. It has the same solution though – rapid emissions reduction. Due to the long lag-times in the system, the quicker we reduce carbon dioxide emissions, the more effect it will have in the future. Tell someone about this problem. Share this document. Visit my website for more information. Do something today!!!