Greenhouse Gas Is Changing Ocean Ecosystems

 

This article originally appeared in Real Change in 2005.  I wrote it about one of my main concerns regarding climate change.   

 

The oceans have buffered the effects of man-made carbon dioxide in the atmosphere, but at a potential cost to the organisms living in the oceans’ upper layers. Scientists at the Pacific Marine Environmental Laboratory on Sand Point Way are part of an international team who discovered that half of the carbon dioxide produced by human industry has ended up in the oceans instead of remaining in the air. They reported their findings last year in the journal Science.

Their research represents the culmination of a 15-year effort to measure and interpret the role of the ocean in the global carbon cycle.

Over the past two centuries, although the amount of man-made carbon dioxide in the atmosphere has steadily increased, only about half of the expected increase was seen. Where the other half went was unknown.

These studies represent “the first time we’ve taken direct measurements to show that the oceans take up man-made carbon dioxide,” says Dr. Chris Sabine, one of the primary authors on the reports. Dr. Richard Feely, another of the lead authors, adds: “These numbers are used to constrain the global carbon cycle models. We need to have these constraints to know if the models are working properly.”

Building accurate models for the movement of carbon dioxide is of particular importance because carbon dioxide acts as a greenhouse gas. As the amount of carbon dioxide in the atmosphere increases, more of the heat from the sun is trapped near the earth’s surface, potentially leading to an increase in average temperatures around the world.

This research also demonstrated the effects of carbon dioxide uptake on the oceans themselves. “People seem to have very strong feelings about global warming,” says Sabine. “But whether you believe in global warming or not, we are adding huge amounts of carbon dioxide to the atmosphere, and that is measurably changing the chemistry of the oceans.”

Carbon dioxide’s potential to affect the environment was recognized over a century ago by the Swedish chemist Svante Arrhenius in 1896. Since then, scientists have struggled to accurately measure and model the global carbon cycle—the movement of carbon dioxide into and out of the many components of the environment such as the forests and the oceans, as well as the man-made inputs from burning fossil fuels, cutting down forests, and producing cement.

Carbon dioxide also deserves particular attention because it has an extremely long retention time in the atmosphere. Once it is released through a process like deforestation, it takes thousands of years for an ecosystem to re-absorb it.

The international team, a coalition between two consortia—the World Ocean Circulation Experiment (WOCE) and the Joint Global Ocean Flux Study (JGOFS)—measured carbon dioxide levels in ocean waters across the globe and at several depths. They compiled measurements demonstrated that the surface waters of the oceans show a net uptake of about 118 billion metric tons of carbon from the air over the past 200 years.

“The surprise was not that the carbon dioxide was there, but how much,” says Feely.

At the same time, the absorbed carbon dioxide is changing the chemistry of ocean waters and jeopardizing some inhabitants’ survival.

As carbon dioxide is absorbed by the upper layers of the ocean, it causes a drop in ocean pH. As this happens, “all organisms that form calcium carbonate shells and skeletons, from [some types of plankton] to the coral reefs—all of these species will have a harder time producing calcium carbonate,” says Feely.

Several studies under controlled laboratory conditions have demonstrated how, when ocean conditions change due to carbon dioxide uptake, marine organisms produce less shell or skeleton material. These experiments suggest the potential for large effects on marine ecosystems.

The actual pH changes are small; according to Sabine, the ocean surface pH has dropped about 0.1 pH unit.

“If anyone’s ever had a fish tank, you know pH is very important to control,” says Sabine. “If you let pH get out of control, all the fish will die.”

While the changes in the oceans’ chemistry should not be that extreme, many of the species that may be affected by reduced pH are at the bottom of the food chain. Changes in these populations could therefore have far-reaching effects.

Feely sees greater problems in the future, given predictions that the amount of carbon dioxide in the atmosphere will likely more than double to 700 to 800 parts per million by the end of the century if changes are not made.

“You would see very significant changes to surface ocean chemistry,” he says.

Some policy makers appear to have noticed. Senator John McCain invited Feely to testify before the Senate Committee on Commerce, Science and Transportation in September of 2004. Sabine described the senators as “very interested” but was unsure about the policy impact the testimony would have.

Feely believes there is a need to decide what to do about man-made carbon dioxide emissions as soon as possible. Carbon dioxide will remain in the atmosphere for millennia, even with a decrease in man-made emissions. “What we do over the next hundred years will affect man over the next several thousand.”

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