Carbon Dioxide Extends Its Harmful Reach to Oceans
By ANDREW C. REVKIN
Published: July 20, 2004
Emissions of carbon dioxide, the main culprit linked to a warming
climate, also pose potential risks to the oceans, new research suggests.
The oceans have absorbed vast amounts of carbon dioxide released
in the industrial age and have measurably changed, chemically and
ecologically, as a result.
In water, carbon dioxide forms carbonic acid. The buildup of the
gas, mainly in the shallow layers of the oceans so far, is reducing
the natural alkalinity of seawater, new studies show. In tank tests,
such conditions can interfere with the reef-building ability of
corals and shell production in some mollusks and tiny plankton.
The most important new research on the marine impact of carbon
dioxide is described in two papers in the current issue of Science.
One study, analyzing 72,000 seawater measurements, found that the
oceans absorbed about 476 billion tons of carbon dioxide from 1800
to 1994, or nearly half the total amount released in that span by
worldwide burning of coal, oil and other fossil fuels, and cement
production.
The second paper concluded that the gas is causing changes in water
chemistry that could expose corals, mollusks and drifting plankton
to conditions that dissolve calcium carbonate, the building block
of reefs and shells.
This paper said that if concentrations of carbon dioxide in the
atmosphere and shallow ocean layers rise as projected over the century,
"the delicate balance of marine planktonic species could undergo
significant shifts" with unknown repercussions.
The authors said they have already measured a substantial expansion
of layers in the seas in which conditions have shifted from those
that foster shell and coral growth to those that cause such materials
to dissolve.
The studies are the culmination of five years of analysis of data
collected through the 1990's by several world-spanning oceanographic
surveys. The lead authors on both papers were Dr. Christopher L.
Sabine and Dr. Richard A. Feely, oceanographers at the National
Oceanic and Atmospheric Administration's Pacific Marine Environmental
Laboratory in Seattle.
Dr. Sabine said the carbon dioxide measurements confirmed that
the oceans have been "performing a tremendous service for humankind"
by sopping up so much of the gas and thus slowing its accumulation
in the atmosphere. But he and Dr. Feely said this service appeared
to be coming with an unanticipated cost: potentially profound impacts
on ocean chemistry and biology.
Several experts not involved with the new studies said they showed
the remarkably broad influence of carbon dioxide emissions.
"These chemical changes and potential impacts on ocean biology
are not something I feel comfortable contemplating," said Dr.
Jorge L. Sarmiento, a professor of atmospheric and oceanic sciences
at Princeton.
The recent shifts in the ocean's carbon dioxide content and chemistry
have come after hundreds of thousands of years of relative stability,
researchers say.
The top layers of the oceans, like the atmosphere, contained fairly
unwavering concentrations of carbon dioxide for more than 400,000
years. During that span concentrations never rose above 280 parts
per million.
But now concentrations are approaching 380 parts per million, and
experts say it will be difficult to avoid a doubling of the pre-industrial
levels by the end of the century.
Over many centuries, as slowly circulating ocean waters mix, the
seas will easily be able to absorb 90 percent or more of the carbon
dioxide liberated by human activities, but the impacts in the short
term could still disrupt marine ecology, Dr. Feely said.
The possible marine effects of carbon dioxide emissions have become
evident only in the last few years, experts said. More than 100
oceanographers and other scientists assessed the issue at a meeting
in May in Paris and, in a statement last week, concluded that "effects
are already occurring."
The participants said the increased absorption of acidic carbon
dioxide by the seas "could have a significant negative effect
on corals and other calcifying organisms, such as shellfish and
some phytoplankton, disrupting marine food webs."
The changes being measured also appeared to be happening at rates
far faster than natural fluctuations, they said.
"By the middle of this century, the accumulating burden of
CO2 entering the ocean will lead to changes in pH or acidity of
the upper layers that are three times greater in magnitude and 100
times faster than those experienced between ice ages," the
participants said in the new concluding report.
The meeting was organized by a branch of the International Council
for Science, a consortium of more than 100 scientific academies
and unions, and the United Nations' International Oceanographic
Commission.
Findings of the meeting are summarized on the Web at http://ioc.unesco.org/iocweb/co2panel/HighOceanCO2.htm.
Credit: NY Times
By ANDREW C. REVKIN
Published: July 20, 2004
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