Ocean Acidification

Pro: Carbon Dioxide is Dangerously Changing Ocean pH

A thriving coral reef. Image licensed from 123RF.com

For more than 200 years, or since the industrial revolution, the concentration of carbon dioxide (CO2) in the atmosphere has increased due to the burning of fossil fuels and land use change. The ocean absorbs about 30 percent of the CO2 that is released in the atmosphere, and as levels of atmospheric CO2 increase, so do the levels in the ocean.

When CO2 is absorbed by seawater, a series of chemical reactions occur resulting in the increased concentration of hydrogen ions. This increase causes the seawater to become more acidic and causes carbonate ions to be relatively less abundant.

Carbonate ions are an important building block of structures such as sea shells and coral skeletons. Decreases in carbonate ions can make building and maintaining shells and other calcium carbonate structures difficult for calcifying organisms such as oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton.

These changes in ocean chemistry can affect the behavior of non-calcifying organisms as well. Certain fish’s ability to detect predators is decreased in more acidic waters. When these organisms are at risk, the entire food web may also be at risk.

Ocean acidification is affecting the entire world’s oceans, including coastal estuaries and waterways. Many economies are dependent on fish and shellfish and people worldwide rely on food from the ocean as their primary source of protein.


Seawater has a pH of 8.2 on average because it contains naturally occurring alkaline ions that come primarily from weathering of continental rocks. When seawater absorbs carbon dioxide from the atmosphere, carbonic acid is produced (see Box 1), reducing the water’s pH. Since the dawn of industrialization, average surface ocean pH has decreased to about 8.1.

Because the pH scale is logarithmic (a change of 1 pH unit represents a tenfold change in acidity), this change represents a 26 percent increase in acidity over roughly 250 years, a rate that is 100 times faster than anything the ocean and its inhabitants have experienced in tens of millions of years.

Acidification can affect many marine organisms, but especially those that build their shells and skeletons from calcium carbonate, such as corals, oysters, clams, mussels, snails, and phytoplankton and zooplankton, the tiny plants and animals that form the base of the marine food web.

These “marine calcifiers” face two potential threats associated with ocean acidification: 1) Their shells and skeletons may dissolve more readily as ocean pH decreases and seawater becomes more corrosive; and 2) When CO2 dissolves in seawater, the water chemistry changes such that fewer carbonate ions, the primary building blocks for shells and skeletons, are available for uptake by marine organisms. Marine organisms that build shells or skeletons usually do so through an internal chemical process that converts bicarbonate to carbonate in order to form calcium carbonate.


Con: Seawater is Alkaline and the Changes are Miniscule and Harmless

Media outlets and science claim that the ocean is “acidifying” due to increased carbon dioxide in the atmosphere. They claim Ocean Acidification1 is dissolving the shells of marine creatures. The measure of acidity and alkalinity in a liquid is called the pH level.

Substances that aren’t acidic or alkaline (that is, neutral solutions) usually have a pH of 7. Acids have a pH that is less than 7. Pure distilled water is 7.0 pH, rainwater is 5.6 pH, soda drinks are 2.5 pH, lemon juice is 2.0 pH, while car battery acid is 0. Household baking soda 9.0 pH, and “Drano” 14.0.

Seawater is naturally alkaline, with a pH ranging from 7.8 to 8.5 with an average of 8.1 —a pH of 7 is neutral—which means that, for now, at least, the oceans are a long way from actually turning acidic.  Since the beginning of the Industrial Revolution in 1850, the pH of surface ocean waters has fallen by 0.1 pH units. If anything, the ocean is becoming more “neutral”, but using the word “acidic” sounds scarier for the cause of climate alarmism.

Media regularly runs wild about dissolving sea creatures in an “acidic” ocean, real world data shows the ocean is still far from acidic.

Although climate models suggest the ocean’s surface pH has dropped from pH 8.2 to 8.1 since 1750 that change was never actually measured. The pH drop is merely a modeled conjecture2 that is, unfortunately, constantly repeated as fact. The concept of pH was first introduced by in 1909 and the pH concept was not modernized in Chemistry until the 1920s. Citrus growers later developed field instruments to measure pH in the 1930s.

Despite our sophisticated global fleet of 3,800 Argo floats that measure ocean temperature and salinity, only 10 percent also measure ocean carbon chemistry, and just 40 floats measure ocean pH suggesting the researchers don’t think it is a really big problem. Measured trends in ocean pH only began in the 1990s, which is far too short a time period to allow a robust analysis.

A new white paper, Ocean Health – Is there an “Acidification” problem? outlines the issue in scientific detail.

The reality is that with an average pH of 8.1, the oceans are a long way from actually turning acidic, but using the word “acidic” instead of more neutral in media reports sounds scarier for the cause of climate alarmism.

Figure 1: Comparison of the pH of common substances. Data source: U.S. Environmental Protection Agency website.

References/Further reading:

  1. What is Ocean Acidification? National Oceanic and Atmospheric Administration, Pacific Marine Environmental Laboratory https://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F
  2. Caldeira, K. & Wickett, M.E., (2005) Ocean model predictions of chemistry changes from carbon dioxide emissions to the atmosphere and ocean. Journal of Geophysical Research, vol. 110. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2004JC002671
  3. Ocean Health – Is there an “Acidification” problem? The CO2 Coalition, May 1st, 2020 http://co2coalition.org/wp-content/uploads/2020/06/Steele-Ocean-Health-White-Paper-final-5-28-20.pdf
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