Thursday, July 3, 2008

Ocean acidification requires action; the science is clear

The science showing the increasing acidification of the oceans is clear and concise—and does not require reliance on complex computer models, a University of Hawai'i researcher reports.

(Image: Coastal Hawaiian coral reef at Nu'alolo, Kaua'i.)

The effects of that acidification on living things is less clear and requires more research, but is sufficient to require humans to limit carbon dioxide emissions, said Richard E. Zeebe, an oceanographer with the UH School of Ocean and Earth Science and Technology.

Zeebe published a paper, “Carbon Emissions and Acidification,” in the journal Science, with co-authors James Zachos of the Earth and Planetary Sciences Department at the University of California at Santa Cruz, Ken Caldeira of the Carnegie Institution's Department of Global Ecology and Toby Tyrell of Southampton University's National Oceanographic Centre in the United Kingdom.

A key message of the paper, is that no matter what happens with climate change, there will be powerful disruptions in the oceans as a result of increasing carbon dioxide in the atmosphere—and carbon dioxide reduction in the atmosphere needs to be an international priority, the authors say.

The subhead to their article said that if the planet expects to avoid environmental damage from acidification of the oceans, it will require “reductions in carbon dioxide emissions regardless of climate change.”

Forty percent of the carbon dioxide produced by humans over the past two centuries has ended up in the oceans. The result is that the oceans become more acid, as carbon dioxide combines with water to form carbonic acid. A more acid ocean is one in which many organisms will have a much more difficult time producing calcite and aragonite, the compounds that make up oyster shells and coral reefs.

The measurement of acidity is the pH scale. Lower means more acid, and higher means more alkaline.

“From experiments we know that small changes in the pH of seawater (0.2-0.3 units) can affect the ability of key marine organisms such as corals and some plankton to build their skeletons and shells. Large areas of the ocean are in danger of exceeding these levels of pH change by the mid 21st century, including reef habitats such as the Hawaiian Islands Coral Reef Reserve,” Zeebe said in an email.

That is a frightening prospect for Hawai'i, where many shorelines are protected by coral reefs and some are even made of old coral reef.

“If we continue with business as usual and don't cut carbon dioxide emissions, carbonate reefs will ultimately start to dissolve. This is basic chemistry,” he said.

There are lots of slings and arrows thrown at climate researchers for the accuracy and dependability of the computerized models they use to predict the impacts of changes in atmospheric chemistry, but the calculation for what happens to ocean chemistry is much simpler, he said.

“Future ocean chemistry projections are largely model-independent on a time scale of a few centuries, mainly because the chemistry of carbon dioxide in seawater is well known and changes in surface ocean carbonate chemistry closely track changes in atmospheric carbon dioxide,” he wrote.

That leaves the issue of how life forms react to the changes.

“The biology is a bit more tricky,” Zeebe wrote.

“Most lab and field experiments show that calcifying organisms struggle under high carbon dioxide conditions but it's very difficult to predict their long-term reaction, let alone responses of entire marine ecosystems.

“Reduced calcification will surely hurt shellfish such as oysters and mussels, with big effects on commercial aquaculture. Other organisms may flourish in the new conditions, but this may include undesirable 'weedy' species or disease organisms,” he wrote.

© 2008 Jan W. TenBruggencate