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CO2 Threatens to Acidify Oceans

Oceans' acidity worries experts

Report: Carbon dioxide on rise, marine life at risk

The Atlanta Journal-Constitution, Sept. 25, 2003

Rising carbon dioxide levels are increasing the acidity of the world's oceans more rapidly than any time since the age of dinosaurs -- adding a worrisome new element to the debate over global environmental change.

Acid rain has long been recognized as a threat to forests, lakes and streams, but a new report, published Wednesday in the British Journal Nature, is the first to raise a flag over the prospect of a more acidic ocean.

The change could threaten the health of everything from microscopic plankton to coral reefs and reach from the surface to the ocean depths.

"If we continue down the path we are going, we will produce changes greater than any experienced in the past 300 million years -- with the possible exception of rare, extreme events such as comet impacts," oceanographer Ken Caldeira, of the Lawrence Livermore National Laboratory, warned Wednesday.

While scientists differ over the effect carbon dioxide and other "greenhouse gases" will have on future climates -- and governments argue over who is to blame -- the trend in carbon dioxide levels is unchallenged.

Continuous measurements of carbon dioxide -- an inevitable byproduct of burning coal, oil and natural gas -- have recorded steadily increasing levels of the gas in the atmosphere every year since 1958, a total rise of 17 percent during that period.

Barring major cuts in automotive and industrial emissions of carbon dioxide, scientists expect the current levels to more than double by the end of the century.

The world's population currently emits about 2 billion tons of carbon dioxide into the air every year, and about one-third of it eventually winds up in the ocean.

Until now, climate experts have taken some comfort in the realization that the oceans can buffer the atmospheric effects of rising carbon dioxide -- such as global warming -- by "scrubbing" carbon from the atmosphere for use by marine plants and animals.

But Caldeira and his colleague Michael Wickett say carbon dioxide removed from the atmosphere enters the oceans in the form of carbonic acid -- the same substance that imparts the fizz to seltzer water and soda pop.

The oceans are now slightly alkaline -- the opposite of acidic. Researchers are not suggesting the seas will become as acidic as soft drinks, but they say the shift toward the acid end of the scale is accelerating.

The change over the last century already matches the magnitude of the change that occurred in the entire 10,000 years preceding the industrial age.

As atmospheric carbon dioxide increases further during the next century -- and more carbonic acid enters the ocean -- Caldeira said the shift will occur more swiftly than any time in the human experience.

Increasingly acid rain from industrial emissions on land has already had devastating consequences for forests, lakes, streams and the fish and other creatures in them.

In the absence of any research on ocean life, the potential impacts are speculative.

"Most ocean life resides near the surface, where the greatest change would be expected to come, but deep ocean life may prove to be even more sensitive to changes," Caldeira said.

Marine plankton and other organisms whose skeletons or shells contain calcium carbonate, which is dissolved by acid solutions, may be particularly vulnerable. Coral reefs -- already suffering from pollution, rising ocean temperatures and other stresses -- are almost entirely calcium carbonate.

"It's difficult to predict what will happen because we haven't really studied the range of impacts," Caldeira said. "But we can say that if we continue business as usual, we are going to see some significant changes in the acidity of the world's oceans."

Alarm over acidifying oceans

New Scientist, Sept. 25, 2003

Climate change may be veering out of control before we understand the consequences, say scientists studying the world's oceans.

If carbon dioxide emissions keep rising, surface waters could become more acidic than they have been for 300 million years - except perhaps during global catastrophes. And this warning follows a report that the biological productivity of the oceans has fallen by six per cent since the 1980s.

"We are changing the chemistry of the ocean and we don't know what it's going to do," says Ken Caldeira, a climate specialist at Lawrence Livermore National Laboratory in California.

As the amount of CO2 in the atmosphere rises, more of the gas reacts with seawater to produce bicarbonate and hydrogen ions, increasing the acidity of the surface layer of water. Ocean pH was 8.3 after the last ice age and 8.2 before CO2 emissions took off in the industrial era. It is now 8.1.

To work out what might happen in the future, Caldeira and his colleague Michael Wickett assumed the "business as usual" scenario, in which CO2 emissions rise with population and economic growth throughout this century, then decline as fossil fuels are exhausted.

In this scenario, atmospheric CO2 levels peak around the year 2300 at 1900 parts per million (ppm), five times as high as today. The researchers calculate that because the ocean will soak up some of this CO2, its surface pH will drop to 7.4 by 2300 and stay that low for hundreds of years (Nature, vol 425, p 365).

Vulnerable creatures

Atmospheric CO2 has risen well above 2000 ppm several times in the past 300 million years. Caldeira says this never pushed ocean pH below 7.5 because carbonate rocks on the seafloor act as a natural buffer, limiting seawater's acidity. But that process takes 10,000 years or so - enough time to neutralise acid deposited by geological processes, but not to deal with the more rapid changes caused by human activity or natural catastrophes such as asteroid impacts.

It is not clear what such a dramatic change in acidity would do to ocean life. But acidity tends to dissolve carbonate, so the most vulnerable creatures will be those with calcium carbonate shells or exoskeletons, such as corals and some algae.

Experiments with double the present CO2 level in the giant, self-contained greenhouse Biosphere 2 showed that the rate of calcium carbonate formation in such animals fell by 40 per cent.

Meanwhile, satellite measurements of chlorophyll levels in the open ocean show that primary productivity - the amount of new biomass being produced from carbon dioxide by photosynthesis - has dropped sharply in the past couple of decades (Geophysical Research Letters, DOI: 10.1029/ 2003GL016889).

Dust clouds

A team led by Watson Gregg of the NASA Goddard Space Flight Center in Greenbelt, Maryland, compared data from two instruments: the Coastal Zone Color Scanner, which worked from 1979 to 1986, and the Sea-viewing Wide Field of View Sensor (SeaWiFS), which has been running since 1997.

Across the globe, the researchers found ocean productivity has dropped by an average of six per cent since the 1980s. There were regional variations, however, and Gregg says there is probably a range of causes.

In northern waters, sea surface temperatures have risen, reducing mixing between layers and decreasing the supply of nutrients to the surface. This may have cut productivity. Meanwhile, extra nutrients deposited from dust clouds may have contributed to higher productivity in equatorial waters.

The drop could just be part of a natural cycle, but Gregg says we know so little about the factors controlling ocean productivity that it is impossible to be sure. He and others warn that by failing to control CO2 levels, we are making a huge leap in the dark.

"We are taking the reins of the geochemical cycles of the Earth," says David Archer, an expert in global carbon cycles from the University of Chicago. "It's really frightening."

Carbon dioxide poisoning the oceans

Study suggests rising acidity in seawater could be irreversible

The San Francisco Chronicle, Sept. 25, 2003

Long-term emissions of carbon dioxide by the world's automobiles, power plants and industries could sharply increase the acidity of the oceans and devastate much of their marine life, scientists at Lawrence Livermore National Laboratory warn.

In a study based on computer models and limited experiments, the Livermore researchers contend that if emissions are not curbed, the acidity of the seas will increase more rapidly over the next 1,000 years than it has over the past 300 million years, and efforts to stave off the damage areunlikely to succeed.

Carbon dioxide emissions are already known as the biggest offenders in global warming, but the new findings by the scientists at one of the Department of Energy's major laboratories point to a wholly different problem - - the increasing acidity of the world's oceans -- that has received scarcely any public attention.

Ken Caldeira, a Livermore climatologist and ocean chemist, and Michael Wickett, a colleague who specializes in computer modeling, are publishing the results of their study today in the journal Nature.

Burning fossil fuels like coal, oil and natural gas are the major culprits in emitting carbon dioxide to the atmosphere. The oceans absorb much of the carbon dioxide, but the chemical reaction with seawater also increases the water's acidity. At current rates, carbon dioxide is entering the atmosphere 50 times more rapidly than it does from natural sources, according to Caldeira, and thus the oceans are rapidly becoming more acidic too.

One computer model that Caldeira and Wickett developed calculated the increase in ocean acidity that would occur over the next 1,000 years if industrial carbon dioxide emissions continued at their present rate. The scientists then used another model based on geological and historical records to estimate the natural rate of past increases in ocean acidity.

The result: It must have taken at least 300 million years for the world's oceans to reach today's natural levels of acidity.

Acid in seawater is particularly harmful to all the marine organisms that contain calcium carbonate in their bodies or in their shells. Particularly endangered would be coral reefs, many types of calcium-containing plankton, and all the shelled marine animals.

In experiments based on the effects of acidic seawater on marine organisms near coastal power plants, Caldeira said that repairing the damage would be unlikely. It might be possible to remediate some of the damage by spreading crushed limestone in a few threatened areas such as Australia's Great Barrier Reef, he said, but reducing acidity in all the world's oceans would probably be impossible.