Around half of all carbon dioxide produced by humans
since the industrial revolution has dissolved into the world's
oceans-with adverse effects for marine life-according to two new
Scientists who undertook the first comprehensive look at ocean
storage of carbon dioxide found that the world's oceans serve as a
massive sink that traps the greenhouse gas.
"The oceans are
performing a great service to humankind by removing this carbon
dioxide from the atmosphere," said Christopher Sabine, a
geophysicist with the National Oceanic and Atmospheric
Administration in Seattle, Washington. "The problem is that this
service has potential consequences for the biology and ecosystem
structure of the oceans."
Of all the carbon dioxide (CO2) emitted into the atmosphere, one
quarter is taken up by land plants, another quarter by the oceans.
Understanding these natural mechanisms is important in forecasting
the rise of atmospheric CO2 because even though plants and bodies of
water now absorb surplus greenhouse gas, they could become new
trouble spots. The ocean absorbs CO2 from the atmosphere in an
attempt to reach equilibrium by direct air-to-sea exchange. This
process takes place at an extremely low rate, measured in hundreds
to thousands of years. However, once dissolved in the ocean, a
carbon atom will stay there, on average, more than 500 years,
estimates Michael McElroy, Butler professor of environmental
Another process, called "the biological pump,"
transfers CO2 from the ocean's surface to its depths. Warm waters at
the surface can hold much less CO2 than can cold waters in the deep.
"This is the 'soda bottle on a warm day' effect," says Agassiz
professor of biological oceanography James McCarthy, "and is not
unique to carbon dioxide; it applies to all gases dissolved in
water. There is a higher capacity to hold a gas with a lower
temperature than with a higher temperature." This means that when
deep ocean waters rise to the surface as part of normal
ocean-circulation patterns, the water heats up and actually releases
A greenhouse gas, carbon dioxide traps solar heat in
Earth's atmosphere. The gas is known as the biggest contributor to
global warming of the planet.
Since mass consumption of fossil fuels began with the industrial
revolution around 1800, the concentration of carbon dioxide in the
atmosphere has grown from an estimated 280 parts per million to
around 380 parts per million.
Today's current level of atmospheric carbon dioxide is only
around half of what scientists have predicted atmospheric levels
should be, based on estimates that humans have contributed 244
billion metric tons of carbon dioxide to Earth's atmosphere.
According to the study by Sabine and his colleagues, the
amount of carbon dioxide the oceans have currently taken up is about
a third of what they can hold. After that, the researchers warn, the
rate of global warming could accelerate.
In the second,
related study, scientists found that while the oceans are helping to
mitigate global warming, the dissolved carbon dioxide is already
having a detrimental effect on marine life.
Based on these
and other studies, we need to be careful about using oceans as a
carbon dioxide sequestion vehicle. We may do much more harm