Carbon dioxide is the catch of the day for an international team
of scientists, whose new study on the oceanic storage of man-made
CO2 may have a profound impact on future studies about global
warming.
Their research, which was published last month in the journal
Science, is the first comprehensive study to measure precisely how
much man-made carbon dioxide has been absorbed by the world’s
oceans over the last 200 years, said Nicolas Gruber a UCLA
assistant professor of atmospheric sciences and a member of
UCLA’s Institute of Geophysics and Planetary Physics.
“What really drives this issue is the concern that
increasing concentration of CO2 in the atmosphere will lead to a
warming of the globe,” Gruber said. He explained how
atmospheric CO2 keeps heat from leaving Earth’s atmosphere,
leading to global warming and climate changes.
Humans have released about 244 billion metric tons of carbon
dioxide into the atmosphere since the industrial age began through
industrial processes such as burning fossil fuels and manufacturing
cement, said Christopher Sabine, an oceanographer at the National
Oceanic and Atmospheric Administration’s Pacific Marine
Environmental Laboratory in Seattle, and lead author of the
study.
The international, decade-long study, which was conducted in the
1990s, shows that approximately 118 billion metric tons of that
atmospheric CO2 has been absorbed by the oceans between 1800 and
1994″”mdash;an amount which represents nearly half of the total
amount of man-made CO2 released over this period, Sabine said.
“We’ve known for a while that the oceans were
absorbing a lot of CO2, but it’s all been based on indirect
methods … This was the first time we’ve been able to
quantify this number using direct measurements (of) inorganic
carbon in the oceans.” Sabine said.
By looking at the fluctuating levels of oceanic CO2, scientists
revealed trends in the way CO2 has been absorbed that were not
apparent in previous, narrower studies, especially relating to the
rate at which carbon dioxide has been taken up by the other major
CO2 absorber””mdash;land plants.
“This is the first time we’ve really tried to put
together a budget including the oceans that looks at the whole
200-year time frame,” Sabine added.
By looking at the carbon dioxide that has been absorbed by the
oceans scientists were surprised to find that land plants must have
released carbon dioxide to bring the total CO2 emissions to 244
billion.
Over the past few decades, scientists have determined that land
plants help to absorb atmospheric CO2, which acts as a fertilizer
for plants under certain conditions, Gruber said.
“What we infer from that is that the land plants were
actually a source of CO2 ““ they’ve been releasing more
CO2 ““ over this 200-year time scale,” Sabine said,
adding that deforestation releases CO2 into the atmosphere as
well.
Determining whether trees release more CO2 than they absorb over
longer periods of time is vital to understanding the rate at which
global warming is taking place on the planet.
But if the recent uptake of carbon dioxide by land plants is a
temporary response to recent efforts to reforest agricultural land,
Sabine continued, the trees may not be able to help us to reduce
the increasing amounts of carbon dioxide in the atmosphere that are
contributing to global warming.
There is no limit to the amount of CO2 the oceans can absorb,
Sabine said. But increasing CO2 concentration in the oceans could
have a profound effect on marine life, said Richard Feely, a
National Oceanic and Atmospheric Administration/Pacific Marine
Environmental Laboratory marine chemist.
Feely is the lead author of the companion paper to the study
which describes how these increases in CO2 concentration make it
difficult for organisms such as coral, swimming snails, and some
sea plants to produce their calcium carbonate shells.
“Many of these species””mdash;for example, the tetrapods,
or swimming snails, are primary food sources for many
fishes,” Feely said.
“These guys form the base of the food web,” Sabine
added, “so how that will propagate up through the food web is
not completely clear, but it could potentially have profound
consequences for a great variety of different organisms.”