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Pollution slowly turning
oceans to acid: report
July 2, 2005
Courtesy the Carnegie Institution
and World Science staff
Pollution could be turning the world’s ocean into acid, a new report says. The reason is that carbon dioxide, a byproduct of human burning of fossil fuels such as coal and
petroleum, turns water acidic.
If carbon dioxide emissions continue to rise, researchers said ocean acidity could increase by the end of
this century to a point at which oceans would be considered mildly acidic. The process has already begun, they added.
“The oceans will become so acidic by 2100 it could threaten marine life in ways we can’t anticipate,” said Ken Caldeira, co-author of the report and scientist at the Carnegie Institution’s Department of Global Ecology in Stanford, California.
The report was released on June 30 by the Royal Society, a
scientific academy in the United Kingdom. (See http://www.royalsoc.ac.uk)
Many scientists view the world’s oceans as an important “sink” for absorbing the human-produced carbon dioxide, a so-called greenhouse gas also considered responsible for global warming. The oceans could thus help slow down global warming, according to this view.
Carbon dioxide also has some benefits for sea creatures.
Marine plants soak up the gas as they breathe it in and convert it to food. Other organisms use it to make their skeletons and
shells.
With the explosion of fossil-fuel burning over the past 200 years, researchers
have estimated that oceans have absorbed more than a third of the human-originated greenhouse gas.
Although sea creatures need some carbon dioxide, Caldeira and colleagues presented research showing too much of it in the ocean could lead to ecological disruption and extinctions.
When the gas dissolves into the ocean it produces carbonic acid. This corrodes shells and can interfere with oxygen
supply, the report said. If current trends continue, the scientists added, acidic water could
disrupt shell and coral formation and hurt organisms dependent on corals and shellfish.
The acidity could also harm organisms that are the most important players at the base of the planet’s food
chain, such as phytoplankton and zooplankton, the researchers said.
“We can predict the magnitude of the acidification based on the evidence that has been collected from the ocean’s surface, the geological and historical record, ocean circulation models, and what’s known about ocean chemistry,” continued Caldeira.
“What we can’t predict is just what acidic oceans mean to ocean ecology and to Earth’s climate. International and governmental bodies must focus on this area before it’s too late.”
Acidity is measured on a scale of 1 to 14, with 7 being neutral and anything lower being acidic.
This means a lower reading on the scale corresponds to more, not less acidity.
The scientists calculated that over the past two centuries, surface seawater acidity has
risen by an amount corresponding to an 0.1 drop on the scale.
There will be another drop by five times that amount by the end of this century, if widely accepted predictions about future carbon dioxide levels hold up, the researchers said. This would bring ocean acidity to a level not seen for millions of years, they added. This acidity level, about 6.5, is generally considered mildly acidic.
The changes in the oceans’ chemistry will also compromise their ability to absorb carbon dioxide from the atmosphere, the researchers said, accelerating global warming.
“This report should sound the alarm bells around the world,” said Chris Field, director of the Carnegie Department of Global Ecology. “It provides compelling evidence for the need for a thorough understanding of the implications of ocean acidification. It also strengthens the case for rapid progress on reducing”
carbon dioxide emissions.
The United States has faced international criticism for its opposition to the Kyoto Protocol, an international
pact to curb such emissions.
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