Ocean acidification is the ongoing decrease in the
pH of the
Earth's oceans, caused by the uptake of
carbon dioxide (CO2) from the
atmosphere.
[2] Seawater is slightly
basic(meaning pH > 7), and ocean acidification involves a shift towards pH-neutral conditions rather than a transition to acidic conditions (pH < 7).
[3] An estimated 30–40% of the carbon dioxide from human activity released into the atmosphere dissolves into oceans, rivers and lakes.
[4][5] To achieve
chemical equilibrium, some of it reacts with the water to form
carbonic acid. Some of the resulting carbonic acid
molecules dissociate into a
bicarbonate ion and a hydrogen ion, thus increasing ocean
acidity (
H+ ion concentration). Between 1751 and 1996, surface ocean pH is estimated to have decreased from approximately 8.25 to 8.14,
[6]representing an increase of almost 30% in H+ion concentration in the world's oceans.
[7][8]Earth System Models project that, within the last decade, ocean acidity exceeded historical analogues
[9] and, in combination with other ocean
biogeochemical changes, could undermine the functioning of marine ecosystems and disrupt the provision of many goods and services associated with the ocean beginning as early as 2100.
[10]
Increasing acidity is thought to have a range of potentially harmful consequences for marine organisms, such as depressing metabolic rates and immune responses in some organisms, and causing
coral bleaching.
[11] By increasing the presence of free hydrogen ions, the additional carbonic acid that forms in the oceans ultimately results in the conversion of carbonate ions into bicarbonate ions. Ocean
alkalinity(roughly equal to [HCO3−] + 2[CO32−]) is not changed by the process, or may increase over long time periods due to
carbonatedissolution.
[12] This net decrease in the amount of
carbonate ions available may make it more difficult for marine calcifying organisms, such as
coral and some
plankton, to form
biogenic calcium carbonate, and such structures become vulnerable to dissolution.
[13] Ongoing acidification of the oceans may threaten future
food chainslinked with the oceans.
[14][15] As members of the
InterAcademy Panel, 105
science academies have issued a statement on ocean acidification recommending that by 2050, global CO2 emissions be reduced by at least 50% compared to the 1990 level.
Ocean acidification has been compared to anthropogenic climate change and called the "evil twin of
global warming" and "the other CO2 problem". Freshwater bodies also appear to be acidifying, although this is a more complex and less obvious phenomenon.
