Environmental Science & Engineering - www.esemag.com - September 2005
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Greenhouse gases causing ocean
to turn more acidic – UK Royal Society
Increasing emissions of carbon
dioxide into the atmosphere are
making the global ocean more
acidic, with potentially catastrophic
and irreversible consequences for
marine life, according to a new report
from Britain’s prestigious Royal
Society.
Over the past 200 years, oceans
have absorbed approximately fifty per
cent of the carbon dioxide that has been
emitted into the atmosphere as a result
of the burning of fossil fuels. When
CO2 enters the ocean, it forms a weak
acid, carbonic acid; calculations by the
Royal Society indicate that this uptake
has led to a reduction in the pH of the
ocean by 0.1 points.
If global emissions of CO2 from
human activities continue to rise on
current trends, says the report, then the
average pH of the oceans could fall by
0.5 units by the year 2100. This pH is
probably lower than has been experienced
for hundreds of millennia and,
critically, this rate of change is probably
one hundred times greater than at
any time over this period. Furthermore,
the report notes, ocean acidification is
essentially irreversible during our lifetimes.
It will take tens of thousands of
years for ocean chemistry to return to a
condition similar to that occurring at
pre-industrial times (about 200 years
ago).
Although predicting and quantifying
the magnitude and impact of such
changes is difficult, the
Royal Society is able to
make some predictions
with a reasonable degree of
certainty. In particular, it
notes that there is convincing
evidence to suggest that
acidification will affect the
process of calcification, by
which animals such as
corals and mollusks make
shells and plates from calcium
carbonate.
The tropical and subtropical
corals are expected
to be among the worst
affected, with implications
for the stability and
longevity of the reefs that they build
and the organisms that depend on them.
Cold-water coral reefs are also likely to
be adversely affected, before they have
been fully explored.
Other calcifying organisms that may
be affected are components of the phytoplankton
and the zooplankton, and
are a major food source for fish and
other animals. Regional variations in
pH will mean that by 2100 the process
of calcification may have become
extremely difficult for these groups of
organisms, particularly in the Southern
Ocean.
There is little evidence that mitigation
techniques such as adding chemicals
is the answer. Such efforts are likely
to be effective only on local levels,
and may anyway cause additional harm
to marine environments.
Reducing CO2 emissions to the
atmosphere appears to be the only practical
way to minimize the risk of largescale
and long-term changes to the
oceans. Action needs to be taken now
to reduce global emissions of CO2 to
the atmosphere to avoid the risk of irreversible
damage to the oceans.
Source: Royal Society. 2005. Ocean
acidification due to increasing
atmospheric carbon dioxide.
The Royal Society, London www.royalsoc.ac.uk
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