Oceans Passing Critical CO2 Threshold, Acidifying

Published on Tuesday, November 25, 2008 by Inter Press Service

Oceans Passing Critical CO2 Threshold
by Stephen Leahy

UXBRIDGE, Canada. An apparent rapid upswing in ocean acidity in recent years is wiping out coastal species like mussels, a new study has found.

Rising carbon dioxide levels in the world’s oceans due to climate change, combined with rising sea temperatures, could accelerate coral bleaching, destroying some reefs before 2050, said an Australian study in January 2002.

“We’re seeing dramatic changes,” said Timothy Wootton of the Department of Ecology and Evolution at the University of Chicago, lead author of the study published Monday in the Proceedings of the National Academy of Sciences. The study shows increases in ocean acidity that are more than 10 times faster than any prediction.

“It appears that we’ve crossed a threshold where the ocean can no longer buffer the effects of CO2 in the atmosphere,” Wootton told IPS.

For millions of years, the levels of carbon dioxide in the atmosphere and the ocean were in balance, but the burning of fossil fuels and deforestation has put more CO2 into the atmosphere over the last 150 years. The oceans have absorbed one-third–about 130 billion tonnes — of those human emissions and have become 30 percent more acidic as the extra CO2 combines with carbonate ions in seawater, forming carbonic acid.

Each day, the oceans absorb 30 million tonnes of CO2, gradually and inevitably increasing their acidity. There is no controversy about this basic chemistry; however, there is disagreement about the rate at which the oceans are becoming acidic and the potential impact.

The ocean’s pH–the measure of acidity or alkalinity–has been declining, or becoming more acidic, at a rate of about 0.02 per decade since 1980, said Ulf Riebesell, a biological oceanographer at the Leibniz Institute of Marine Sciences in Kiel, Germany.

“We’re just starting to realise the far-reaching impacts of ocean acidification,” Riebesell told IPS, noting that the term ocean acidification was coined just four years ago.

Wootton and colleagues measured a massive pH decline of 0.4 units in just eight years off the northwest tip of Washington State in the U.S. And that abrupt increase has had a major impact on marine species in the tide pool on Tatoosh Island where the study was conducted.

“Large shell species like mussels and goose barnacles were dying at a faster rate and being replaced by other species,” he said.

Increased seawater acidity means there is less calcium carbonate in the water for corals and shell-forming species like mussels and phytoplankton to grow or maintain their skeletons. The once verdant mussel beds in the study area were being replaced by algae, Wootton said.

“We are not exactly certain why the mussels declined but preliminary evidence has shown some thinning of shells on snails in the area,” he told IPS.

Wootton also cautions that the results are just from one area, but said there have been other regions where large increases in the rate of ocean acidity have been measured along the entire west coast of North America. However, none have been as large or consistent as those at Tatoosh Island.

“We measured even greater increases in acidity this summer,” he said. “I’m really getting worried now.”

Riebesell and other ocean acidification experts contacted by IPS say atmospheric CO2 could not be responsible for the large increase Wootton measured. Either their methodology is flawed or there is some local anomaly that is skewing the results, they said.

“If the pH change is real…a likely explanation would be that also other factors related to seawater pH have changed over the eight-year period in the tidal pool,” said Riebesell.

Wootton told IPS they looked for other causes of both the declines in mussels and other species and the high acidity levels. They could find no other explanation.

Ocean acidification is a very new field of science and the best ways to do research are still being investigated. In fact, the Leibniz Institute of Marine Sciences was host to an international workshop on that very topic last week, said Riebesell. A draft outline of a guide for Best Practices in Ocean Acidification Research and Data Reporting will be forthcoming.

This dispute aside, marine scientists are very worried about ocean acidification and the potential to decimate corals and a large number other species. Some have suggested that little will be left in the oceans except bacteria, jellyfish and algae without major reductions in emissions of fossil fuels and an end to deforestation.

“CO2 is making the oceans very sick,” said Jackie Savitz, senior campaign director for Oceana’s Pollution Campaigns. Oceana is an international ocean conservation group.

“There is a strong likelihood of a massive extinction of corals by mid-century,” Savitz said in an interview.

To prevent this, atmospheric CO2 concentrations need to return to 350 parts per million, the pre-industrial level, she said. Currently CO2 is 385 ppm and growing at 2 to 3 ppm annually. The Intergovernmental Panel on Climate Change, European Union and others have called for a climate stabilisation of 450 ppm to ward off the worst affects of climate change.

“Four hundred and fifty ppm is not going to save corals,” she said, because the acidification of the ocean would kill and weaken corals and other species that make up the reef ecosystems. “We need to stop using fossil fuels period. Carbon that’s in the ground now should stay there.”

Some leading climates scientists agree.

In study published last week, 10 prominent scientists said that the level of globe-warming carbon dioxide in the air has probably already reached a point where world climate will change disastrously unless the level can be reduced to 350 ppm. The study is a departure from recent estimates that truly dangerous levels would be reached only later in this century.

Climate feedbacks have already begun, particularly at the poles, accelerating the warming of the planet, said lead author James E. Hansen, director of the Goddard Institute for Space Studies, part of Columbia University’s Earth Institute.

Ocean acidification is scary, acknowledges Riebesell. Acidification cannot be fixed quickly. It might take a thousand years for the oceans to regain their buffering capacity to prevent continuing acidification. Many species will not be able to adapt and there will be no place to hide, he said.

“The oceans will be very different in 20 years,” he warned.

© 2008 Inter Press Service


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