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Ocean acidification

The meaning of «ocean acidification»

Ocean acidification is the ongoing decrease in the pH value of the Earth's oceans, caused by the uptake of carbon dioxide (CO2) from the atmosphere.[2] The main cause of ocean acidification is the burning of fossil fuels. Ocean acidification is one of several effects of climate change on oceans. 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] The concern with ocean acidification is that it can lead to the decreased production of the shells of shellfish and other aquatic life with calcium carbonate shells, as well as some other physiological challenges for marine organisms. The calcium carbonate shelled organisms can not reproduce under high saturated acidotic waters. An estimated 30–40% of the carbon dioxide from human activity released into the atmosphere dissolves into oceans, rivers and lakes.[4][5] 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, the pH value of the ocean surface 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 (note the pH scale is logarithmic so a change of one in pH unit is equivalent to a ten fold change in H+ ion concentration).[7][8] 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.[9] 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 carbonate dissolution.[10] 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.[11] Ongoing acidification of the oceans may threaten future food chains linked with the oceans.[12][13]

Ocean acidification has been compared to anthropogenic climate change and called the "evil twin of global warming"[14][15][16][17][18] and "the other CO2 problem".[15][17][19] Freshwater bodies also appear to be acidifying, although this is a more complex and less obvious phenomenon.[20][21] To ensure that ocean acidification is minimized, the United Nation's Sustainable Development Goal 14 ("Life below Water") aims to ensure that oceans are conserved and sustainably used.[22] 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.[23]

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