Focus on responding to climate change: ocean acidification

This focus sheet defines ocean acidification and explains the impacts it has on marine organisms, particularly those that form shells.

What is ocean acidification?

The world’s oceans absorb carbon dioxide (CO2) from the atmosphere. As the oceans soak up excess carbon emissions, the chemistry of the seawater changes — both locally and globally. This absorption process alters the ocean’s natural state and forces the acid-base balance of ocean waters toward acidity. This move toward the lower end of the pH scale is called ocean acidification.

Over the past 250 years, surface oceans have absorbed about 550 billion tons of CO2 emissions from the atmosphere, or about one third of total carbon emissions created by human activity. The absorption of carbon dioxide in the ocean directly impacts the chemistry and biology of the oceans. If carbon emissions increase as forecasted for the next forty years, the resulting ocean acidity levels will exceed any experienced in millions of years.