Stabilising current CO2 emission levels not enough to save coral reefs

September 23rd, 2008 - 4:26 pm ICT by IANS  

Washington, Sep 23 (IANS) Even if greenhouse gas emission is stabilised at current levels, it would still be enough to cause acidification of oceans and sound the death knell of coral reefs.Ocean acidification could devastate coral reefs and other marine ecosystems even if atmospheric carbon dioxide (CO2) stabilizes at 450 parts per million (PPM), a level well below that of many climate change forecasts.

Chemical oceanographers Long Cao and Ken Caldeira of the Carnegie Institution’s Department of Global Ecology, based these findings on computer simulations of ocean chemistry stabilised at atmospheric CO2 levels ranging from 280 PPM (pre-industrial levels) to 2,000 PPM.

Present levels are 380 PPM and rapidly rising due to accelerating emissions from human activities, primarily the burning of fossil fuels, reports Eurekalert.

This study was initiated as a result of Caldeira’s testimony before a Congressional subcommittee on Fisheries, Wildlife and Oceans in April of 2007.

At that time he was asked what stabilisation level would be needed to preserve the marine environment, but had to answer that no such study had yet addressed that question. Cao and Caldeira’s study helps fill the gap.

Atmospheric CO2 absorbed by the oceans’ surface water produces carbonic acid, the same acid that gives soft drinks their fizz, making certain carbonate minerals dissolve more readily in seawater.

This is especially true for aragonite, the mineral used by corals and many other marine organisms to grow their skeletons. For corals to be able to build reefs, which requires rapid growth and strong skeletons, the surrounding water needs to be highly supersaturated with aragonite.

“Before the industrial revolution, over 98 percent of warm water coral reefs were surrounded by open ocean waters at least 3.5 times supersaturated with aragonite,” said Cao.

“But even if atmospheric CO2 stabilises at the current level of 380 ppm, fewer than half of existing coral reef will remain in such an environment. If the levels stabilize at 450 ppm, fewer than 10 percent of reefs would be in waters with the kind of chemistry that has sustained coral reefs in the past.”

“If current trends in CO2 emissions continue unabated,” says Caldeira, “in the next few decades, we will produce chemical conditions in the oceans that have not been seen for tens of millions of years. We are doing something very profound to our oceans.”

These findings were published in Geophysical Research Letters.

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