Higher acidity levels are especially problematic for creatures such as oysters, because they slow the growth of their shells. Experiments have shown other animals, such as clown fish, also suffer. In a study that mimicked the level of acidity scientists expect by the end of the century, clown fish began swimming toward predators, instead of away from them, because their sense of smell had been dulled.
Scientists initially assumed that the carbon dioxide absorbed by the water would be sufficiently diluted as the oceans mixed shallow and deeper waters. But most of the carbon dioxide and the subsequent chemical changes are being concentrated in surface waters.
Atmospheric carbon dioxide levels are already more than one-third greater than preindustrial concentrations, and if fossil fuel consumption continues unabated, it could double or triple before the end of this century. The resulting surface ocean acidification would represent an additional 0.3 to 0.4 pH drop, larger and more rapid than anything experienced by sea life for tens of millions of years. The most sensitive areas may be the surface subpolar North Pacific, the Southern Ocean, and at middepth along the Pacific continental shelf and margin, where waters are already closer to being corrosive for carbonate shells.
Burning gasoline in cars or using electricity from a natural gas or coal-fired power plant releases carbon dioxide gas into the air, some of which eventually dissolves in the ocean, where it forms carbonic acid and a series of dissociation products. The release of hydrogen ions from the breakdown of carbonic acid lowers the pH of seawater, causing the normally somewhat alkaline water (surface pH about 8.2) to become more acidic.
Ocean acidification is likely to alter the biodiversity of the world’s marine ecosystems and may affect the total productivity of the oceans. Previously it was thought that these changes would take centuries, but new findings indicate that an increasingly acidic environment could cause problems in high-latitude marine ecosystems within just a few decades.
Ocean acidification has been called a sister problem to climate change because it is caused by the same human-caused production of large amounts of CO2. Its impacts are additional to, and may exacerbate, the effects of climate change.
“In some regions, the man-made rate of change in ocean acidity since the Industrial Revolution is a hundred times greater than the natural rate of change between the Last Glacial Maximum and pre-industrial times,” emphasized Tobias Friedrich [an International Pacific Research Center scientist]. The Earth warmed slowly after the last ice age, allowing marine ecosystems ample time to adjust as the level of CO2 rose over 6,000 years. Now, they face a similar increase in CO2 concentration in just 100–200 years.
CO2 is absorbed by the ocean, where it reacts with the seawater, increasing the water’s acidity. As acidity of seawater rises, the saturation level of aragonite drops. Lower aragonite levels may significantly reduce the calcification rate of marine organisms, resulting in the potential loss of ecosystem.
Ocean acidification threatens species throughout the web who feed on these creatures – from salmon to whales.
By the time atmospheric CO2 doubles from the pre-industrial era (expected by 2050), tropical coral reefs may stop growing and start to dissolve. Some scientists predict that they will become extinct.
The ocean’s acidity has increased 30 percent since pre-industrial times. Scientists predict that it will increase 150-185 percent by the end of the century if we don’t reduce our CO2 emissions.