By ScienceDaily, August 1, 2012
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| As carbon emissions by human activities have increased (purple), some carbon has stayed in the atmosphere (red) and some has been absorbed by natural “sinks” on land and in the oceans (blue). Natural sinks, including land ecosystems and the oceans, remove about half of the carbon emitted by human activities back out of the atmosphere. Note: The graph depicts carbon accumulation, which is proportional to carbon dioxide |
Earth's oceans,
forests and other ecosystems continue to soak up about half the carbon dioxide
emitted into the atmosphere by human activities, even as those emissions have
increased, according to a study by University of Colorado and NOAA scientists
published August 1 in the journal Nature.
The scientists
analyzed 50 years of global carbon dioxide (CO2) measurements and
found that the processes by which the planet's oceans and ecosystems absorb the
greenhouse gas are not yet at capacity.
"Globally,
these carbon dioxide 'sinks' have roughly kept pace with emissions from human
activities, continuing to draw about half of the emitted CO2 back
out of the atmosphere. However, we do not expect this to continue
indefinitely," said NOAA's Pieter Tans, a climate researcher with NOAA's
Earth System Research Laboratory in Boulder, Colo., and co-author of the study.
The University of Colorado's Ashley Ballantyne is lead author.
Carbon dioxide is
emitted into the atmosphere mainly by fossil fuel combustion but also by forest
fires and some natural processes. The gas can also be pulled out of the
atmosphere into the tissues of growing plants or absorbed by the waters of
Earth's oceans. A series of recent studies suggested that natural sinks of carbon
dioxide might no longer be keeping up with the increasing rate of emissions. If
that were to happen, it would cause a faster-than-expected rise in atmospheric
carbon dioxide and projected climate change impacts.
Ballantyne, Tans
and their colleagues saw no faster-than-expected rise, however. Their estimate
showed that overall, oceans and natural ecosystems continue to pull about half
of people's carbon dioxide emissions out of the atmosphere. Since emissions of
CO2 have increased substantially since 1960, Ballantyne said,
"Earth is taking up twice as much CO2 today as it was 50 years
ago."
The rest continues
to accumulate in the atmosphere, where it is likely to accelerate global
warming.
This new global
analysis makes it clear that scientists do not yet understand well enough the
processes by which ecosystems of the world are removing CO2 from the
atmosphere, or the relative importance of possible sinks: regrowing forests on
different continents, for example, or changing absorption of carbon dioxide by
various ocean regions.
"Since we
don't know why or where this process is happening, we cannot count on it,"
Tans said. "We need to identify what's going on here, so that we can
improve our projections of future CO2 levels and how climate change
will progress in the future."
Tans, Ballantyne
and colleagues at the University of Colorado, including the Cooperative
Institute for Research in Environmental Sciences, dissected the long-term
records of CO2 levels measured by NOAA and the Scripps Institution
of Oceanography at remote sites around the world, including the top of a
mountain in Hawaii and the South Pole. Those CO2 levels reflect
global averages of the greenhouse gas, which are affected by natural cycles as
well as people's activities.
The researchers
also scrutinized national and international inventories or bookkeeping
estimates of CO2 emissions by people and compared those to the
increasing atmospheric levels of the gas.
"The
uptake of carbon dioxide by the oceans and by ecosystems is expected to slow
down gradually," Tans said. Oceans, for example, are already becoming more
acidic as they absorb about a quarter of the carbon dioxide pumped into the air
by human activities. "As the oceans acidify, we know it becomes harder to
stuff even more CO2 into the oceans," Tans said. "We just
don't see a letup, globally, yet."
Story Source:
The above story is reprinted from materials provided by National Oceanic and Atmospheric Administration.Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
- A. P. Ballantyne, C. B. Alden, J. B. Miller, P. P. Tans, J. W. C. White. Increase in observed net carbon dioxide uptake by land and oceans during the past 50 years.Nature, 2012; 488 (7409): 70 DOI: 10.1038/nature11299
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