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Ocean acidification


  • Ocean surface pH has declined from 8.2 to below 8.1 over the industrial era as a result of the increase in atmospheric CO2 concentrations. This decline corresponds to an increase in oceanic acidity of about 30 %.
  • Ocean acidification in recent decades has been occurring 100 times faster than during past natural events over the last 55 million years.
  • Observed reductions in surface water pH are nearly identical across the global ocean and throughout continental European seas, except for variations near the coast. The pH reduction in the northernmost European seas, i.e. the Norwegian Sea and the Greenland Sea, is larger than the global average.
  • Ocean acidification already reaches into the deep ocean, particularly at the high latitudes.
  • Models consistently project further ocean acidification worldwide. Ocean surface pH is projected to decrease to values between 8.05 and 7.75 by the end of 21st century, depending on future CO2 emissions levels. The largest projected decline represents more than a doubling in acidity.
  • Ocean acidification is affecting marine organisms and this could alter marine ecosystems.

Reference information



acidity, clim043, ocean

Climate impacts

Extreme Temperatures, Water Scarcity


Adaptation Measures and Actions, Observations and Scenarios


Marine and Fisheries

Geographic characterization


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