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What is ocean acidification?
From a chemical point of view, seawater is an aqueous solution and therefore also has a pH value that shows how acidic or basic the liquid is.
Values below seven are called acidic, while values above seven are basic.
Since this division is logarithmic, a change by a value of one means that the amount of acid molecules already increases or decreases tenfold.
The current pH of the surface water of the oceans is around 8.1, so they are slightly basic.
What is the connection to climate change?
About thirty percent of the carbon dioxide emitted does not stay in the atmosphere, but is absorbed by the oceans in the form of carbonic acid.
Without this buffer effect, the current temperature rise would be even greater.
However, this also has a negative effect: with increasing CO2 emissions, the oceans become more acidic, so their pH value drops.
It has already fallen by 0.1 since the beginning of industrialization.
This sounds like a small change, but based on the logarithmic data it means that the number of acid molecules has increased by around thirty percent.
According to the Intergovernmental Panel on Climate Change, the pH value of seawater could even drop to 7.8 by 2100.
This acidification of the water also reduces the proportion of carbonate ions that are important for the formation of calcareous skeletons and shells and that contain carbon - with direct effects on marine life such as mussels and corals.
Even more serious, however, are the adverse effects on plankton organisms, which only have very thin calcareous shells.
They not only form an important basis for the marine food chain: when their shells sink to the sea floor, carbon dioxide is indirectly withdrawn from the carbon cycle in the long term.
So they represent a CO2 sink. If there are fewer of these plankton organisms at the end due to the acidification or if they form thinner shells, then in turn less CO2 is permanently bound here.
Together with rising water temperatures and falling oxygen levels, ocean acidification forms a “deadly trio” for countless creatures in the world's oceans.
For this reason, experts often refer to it as the "bad little brother" of global warming.
Previous climate term: tilting elements.