The oceans have absorbed almost one-half (approximately 525 billion tons) of human-released CO2 emissions since the Industrial Revolution. Although this has moderated the effect of greenhouse gas emissions, it is chemically altering marine ecosystems 100 times more rapidly than it has changed in at least the last 650,000 years.1 Recent studies suggest that the oceans are becoming less able to absorb as much carbon dioxide as they have in the past, decreasing their ability to buffer against climate change.2,3 By absorbing massive amounts of carbon dioxide, the pH (a measure of acidity) in ocean surface waters has dropped approximately 30%. As CO2 dissolves in the ocean, the water becomes more acidic and the amount of dissolved carbonate available for calcium carbonate shell and skeleton formation – important to corals, plankton and shellfish – decreases.
Naturally, the oceans are alkaline, meaning they are above 7 on the pH scale (7 is neutral, below 7 is acidic, and above 7 is alkaline). Prior to industrialization, the pH of the oceans was on average about 8.2; however, since then, the average pH has dropped about 0.1 units. While this may seem like a small change, it actually represents a 26 percent increase in acidity.
The IPCC determined that according to mid-range projections (522 ppm CO2 in 2050) for future emissions of CO2, the pH of the oceans will decline an additional 0.3-0.4 units by 2100, becoming 2 to 2.5 times more acidic than pre-industrial levels.4 Marine life as we know it, is not adapted to these conditions.
Scientists are working to determine the full extent of the problems associated with acidification. However, they know that many marine plants and animals are at risk from rapid acidification. Without effective and efficient action, it will take the oceans thousands of years to reestablish chemical conditions that resemble those found today.