A recent letter dismissed scientific concern over increasing ocean acidity as a consequence of rising atmospheric carbon dioxide levels. I am writing to correct the scientific errors in this letter.
When dissolved in water, carbon dioxide produces carbonic acid. The ocean is the single biggest natural sink for the excess carbon dioxide we put into the atmosphere. The observed oceanic pH (a measure of acidity) reduction since preindustrial times is well understood to be overwhelmingly due to carbon dioxide (not mercury and sulphates as claimed by the writer).
Corals, certain types of plankton, mollusks such as mussels or oysters, and crustaceans such as crabs or lobsters all have shells made of calcium carbonate. The formation of these shells is very sensitive to the amount of carbon dioxide dissolved in the ocean. As ocean acidity increases, many species will find that it will be difficult for them to grow shells. At high enough levels of carbon dioxide, the shells in some living species would actually start to dissolve.
We can do a simple experiment at home to watch this in action. All you have to do is drop some chalk into carbonated water. The chalk, which is made of calcium carbonate, starts to dissolve. Dropping the same chalk in regular tap water has no effect.
The current rate of change in ocean acidity poses a problem for marine organisms. The current rate is unparalleled in at least the last 65 million years. It is 10 times faster than occurred 55 million years ago during a major deep ocean extinction event. If unchecked, human emissions of carbon dioxide are on track to take ocean acidity by end of the 22nd century to levels that have not been seen for at least 300 million years. It takes thousands of years for atmospheric carbon dioxide levels to drop and many thousands more for the ocean to become rebalanced.
Increasing ocean acidity and its potential effect on resident ecosystems is an extremely serious, indirect consequence of our increasing atmospheric carbon dioxide emissions. To dismiss so flippantly Elizabeth May, who takes the science seriously, does a disservice to the public discourse on what, if anything, society should do to mitigate against global warming and ultimately the collapse of existing ecosystems.
Andrew Weaver
Victoria
