Oceans have the capacity to absorb large amounts of carbon dioxide (CO2) because CO2 dissolves and reacts in seawater to form bicarbonate (HCO3−) and protons (H+). About a quarter to a third of the CO2 emitted into the atmosphere from the burning of fossil fuels, cement manufacturing, and land use changes has been absorbed by the oceans. Over thousands of years, the changes in pH have been buffered by bases, such as carbonate ions (CO32−). However, the rate at which CO2 is currently being absorbed into the oceans is too rapid to be buffered sufficiently to prevent substantial changes in ocean pH and CO32−. As a consequence, the relative seawater concentrations of CO2, HCO3–, CO32−, and pH have been altered. Since preindustrial times, the ocean pH has decreased by a global average of 0.1. It is estimated that unmitigated CO2 emissions will cause ocean pH to decrease by as much as 0.4 by 2100 and 0.77 by 2300. These will be the most rapid and greatest changes in ocean carbonate chemistry experienced by marine organisms over the past tens of millions of years. Laboratory experiments, field observations of natural CO2-rich seawater “hot spots,” and studies of previous ocean acidification in Earth’s history indicate that these changes are a threat to the survival of many marine organisms but particularly organisms that use CaCO3 to produce shells, tests, and skeletons. The only way of reducing the impacts of ocean acidification on a global scale is through urgent and substantial reductions in anthropogenic CO2 emissions. Ocean acidification is a key argument for united global societal action in ongoing climate change negotiations.
Findlay H. S. & Turley C., 2021. Chapter 13 – Ocean acidification and climate change. In: Letcher T. M. (Ed.), Climate change – observed impacts on planet earth, pp 251-279. Amsterdam: Elsevier. Chapter (restricted access).