Uncovering the Problem

Scleractinian coral exposed for one year to (a) seawater pH 8.2 and (b) acidified seawater pH 7.4. Credit: Fine & Tchernov (2007).

A software developer turned climate scientist helped coin the term “ocean acidification.” Ken Caldeira, then a consultant for the Department of Energy, was studying the potential for burying carbon emissions in the deep sea and how that might affect ocean pH (Kolbert, 2006). He compared his results to the current changes happening at the ocean surface from normal carbon emissions. He submitted his work to Nature, but his editors were so intrigued by his surface ocean calculations they asked him to scrap the deep-sea research. The subtitle of Caldeira’s subsequent paper was alarming: “The coming centuries may see more ocean acidification than the past 300 million years.” In the 2003 paper, Caldeira’s model predicted a drop of .4 pH units by 2100 and .7 units by 2250.

Since then, Caldeira has become an outspoken advocate for the oceans. He likes to compare what’s happening today to the time 65 million years ago when an asteroid struck the earth and carbon dioxide levels rose dramatically, causing ocean acidification and mass extinctions.

“Nearly everything with a calcium carbonate shell or skeleton disappeared,” he told a US House of Representatives committee last year. “Coral reefs weren’t seen again for two million years. You have to go back to events like this, many tens of millions of years ago, to find anything comparable to what we are doing to ocean chemistry today with our carbon dioxide emissions.”

Much of what’s known about corals in an acidifying ocean was discovered in the Arizona desert in the 1990s, in a sealed environment designed to mimic conditions on Earth, called Biosphere 2. Here, in a world with a fake ocean and atmosphere, eight people lived for two years. Over time, carbon dioxide levels soared and the pH of the “ocean,” simulated inside a stainless-steel tank, dropped.

A then-Columbia University scientist, Chris Langdon, tried to correct the ocean’s pH by adding baking soda and baking powder. Boosting the alkalinity not only restored pH but also restored coral growth. To test his hypothesis, that coral reef-building depended on the saturation state of water, he spent three years measuring coral growth in varied states of saturation. His paper, published in 2000, generated such a stir that he spent another two years replicating the results. In a 2003 paper published in the journal Global Biogeochemical Cycles, he found that calcification declined 800 percent in response to an elevated atmospheric carbon dioxide level of 658 ppm.

A German marine biologist, Ulf Riebesell, documented a similar effect on coccolithophores, a species of phytoplankton covered in plate-like armor made of calcite (Kolbert, 2006).

The urgency of the problem became apparent. In 2004, scientists from around the world gathered for the first-ever symposium on ocean acidification to compare notes and discuss research priorities for the future. The journal Nature called it, “a turning point in expanding awareness among scientists about acidification.”

At the second symposium, held last year in Monaco, more than 150 top researchers signed a declaration that received wide media attention: “We scientists who met in Monaco to review what is known about ocean acidification declare that we are deeply concerned by recent, rapid changes in ocean chemistry and their potential, within decades, to severely affect marine organisms, food webs, biodiversity and fisheries.”

“The chemistry is so fundamental and changes so rapid and severe that impacts on organisms appear unavoidable,” James Orr, chairman of the symposium, told the BBC.  “The questions are now how bad will it be and how soon will it happen.”


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