Global warming's evil twin threatens West Coast fishing grounds

Within the next few decades, ocean acidification ? an effect of global warming ? could leave sea creatures along the West Coast unable to maintain their protective shells, according to a new study.

By Pete Spotts,?Staff writer / June 14, 2012

A couple sits on a park bench and watches the setting sun on the Pacific Ocean in Encinitas, Calif., June 5.

Mike Blake/Reuters

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Over the next few decades, coastal waters off of California, Oregon, and Washington are in danger of becoming acidic enough to harm the rich fisheries and diverse marine ecosystems there, according to a new study. Blame it on global warming's evil twin.

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The process changing the seas' chemistry has been dubbed "ocean acidification." It refers to the impact that rising carbon dioxide levels in the atmosphere are having on seawater. CO2 levels are increasing as humans burn fossil fuel and change land-use patterns. The oceans absorb up to 26 percent of those emissions ? a number that is expected to go up as the Arctic Ocean loses more of its summer sea-ice cover.

By 2050, the team conducting the study estimates, more than half the near-shore waters governed by the California Current system are likely to become so acidic throughout the year that many shell-building organisms will be unable to maintain their armor?. That point could come within the next 20 to 30 years for some sea-floor habitats on the continental shelf, the researchers estimate.

While the team anticipated it would see marine conditions deteriorate with rising atmospheric CO2 levels, "I was really surprised to see how quickly some of these changes will be occurring," says Nicolas Gruber, a biogeochemist at the Swiss Institute of Technology in Zurich who led the team.

The team "points out fairly clearly that if it wasn't for anthropogenic carbon, we wouldn't be passing that tipping point" from encroaching, acidic water, says Richard Feely, a senior scientist at the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory in in Seattle. "That's a very important part of that paper."

Although the study doesn't directly address the question of which creatures get hit hardest first, the team does suggest that other studies indicate oysters could be vulnerable, especially as juveniles. Still, the team acknowledges that some organisms are hurt by even small changes in acidity, while others can tolerate larger changes, at least for relatively short periods of time.

The results were posted Thursday on ScienceExpress, the online outlet for research journal Science. Science will publish the results in paper form later.

A delicate environment

To some, the phrase "ocean acidification" may trigger visions of house keys melting in the surf. While the changes are more subtle than that, at least on a human scale, they can harmful to many forms of marine life.

As CO2 dissolves in the ocean, seawater gradually acidifies. Shell-building marine creatures ? ranging from tiny plankton to headliners for bouillabaisse and bisque ? have a far more difficult time building and maintaining their protective shells. The tiny creatures that build coral reefs also have a harder time drawing on the chemical construction materials once available to them.

In this new research, Dr. Gruber's team conducted modeling studies of the effect that rising CO2 levels are likely to have on ocean chemistry along a stretch of coastline influenced by the California Current system, which runs from that runs long the West Coast from British Columbia through the southern end of Baja California. The area the team focused on stretches from Point Conception, near Santa Barbara, northward to the California-Oregon border.

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