What is Ocean Acidification?
Since the beginning of the industrial revolution the release of carbon dioxide (CO2
from human activities has resulted in atmospheric CO2
concentrations that have increased
from approximately 280 to 385 parts per million (ppm). The atmospheric concentration of
is now higher than experienced on Earth for at least the last 800,000 years and
probably over 20 million years, and is expected to continue to rise at an increasing rate,
leading to significant temperature increases in the atmosphere and oceans in the coming decades.
The oceans have absorbed approximately 525 billion tons of carbon dioxide from the atmosphere,
or about one third of the anthropogenic carbon emissions released. This absorption has benefited
humankind by significantly reducing the greenhouse gas levels in the atmosphere and minimizing
some of the impacts of global warming. However, the ocean's uptake of carbon dioxide is having
negative impacts on the chemistry and biology of the oceans. Hydrographic surveys and modeling
studies have revealed that the chemical changes in seawater resulting from the absorption of
carbon dioxide are lowering seawater pH. The pH of ocean surface waters has already decreased
by about 0.1 units from an average of about 8.21 to 8.10 since the beginning of the industrial
revolution. Estimates of future atmospheric and oceanic carbon dioxide concentrations,
based on the Intergovernmental Panel on Climate Change (IPCC) CO2
emission scenarios and coupled ocean-atmosphere models, suggest that by the middle of this
century atmospheric carbon dioxide levels could reach more than 500 ppm, and near the end
of the century they could be over 800 ppm. This would result in an additional surface
water pH decrease of approximately 0.3 pH units by 2100.
reacts with seawater, the reduction in seawater pH also reduces the availability of carbonate
ions, which play an important role in shell formation for a number of marine organisms such
as corals, marine plankton, and shellfish. This phenomenon, which is commonly called "ocean acidification,"
could have profound impacts on some of the most fundamental biological and geochemical
processes of the sea in coming decades. Some of the smaller calcifying organisms are
important food sources for higher marine organisms. Declining coral reefs due to
increases in temperature and decreases in carbonate ion would have negative impacts
on tourism and fisheries. Abundance of commercially important shellfish species may
also decline and negative impacts on finfish may occur. This rapidly emerging scientific
issue and possible ecological impacts have raised serious concerns across the scientific
and fisheries resource management communities.
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