http://news.xinhuanet.com/english/2005-11/25/content_3834995.htm
Xinhua - English
Carbon dioxide levels highest in 650,000 years: studies
www.chinaview.cn 2005-11-25 16:44:24
LOS ANGELES, Nov. 25 (Xinhuanet) -- With the first in-depth
analysis of the air bubbles trapped in the ice core of east
Antarctica, scientists have discovered that today's atmospheric
carbon dioxide levels are the highest in 650,000 years.
The analysis highlights the fact that today's rising atmospheric
carbon dioxide concentration, at 380 parts per million by volume, is
already 27 percent higher than its highest recorded level during the
last 650,000 years, reported scientists in two papers in the Nov. 25
issue of the journal Science.
One study chronicles the stable relationship between climate and
the carbon cycle during the Pleistocene (650,000 to 390,000 years
ago). The second paper documents atmospheric methane and nitrous
oxide levels over the same period.
Carbon dioxide and methane, known as greenhouse gases, are blamed
for global warming. Scientists believe that humans have been
accelerating the global warming trend by emitting more greenhouse gas
through industrialization.
The ice core from Antarctica, containing hundreds of thousands of
years-worth of atmospheric air samples within tiny bubbles trapped in
the ice, adds to this argument by extending Earth's greenhouse gas
record by 210,000 years.
The new records should help scientists better understand climate
change and the nature of the current warm period on Earth, and may
also aid researchers in reducing uncertainty in predictions of future
climate change, said the researchers.
"We have added another piece of information showing that the
timescales on which humans have changed the composition of the
atmosphere are extremely short compared to the natural time cycles of
the climate system," Thomas Stocker, senior author for both studies,
said in a statement.
The new studies confirm the stable relationship between the
Antarctic climate and greenhouse gases carbon dioxide and methane
during the last four glacial cycles.
The ice core analysis also extends this relationship back another
two glacial cycles, to a time when the warm "interglacial" periods
were milder and longer than more recent warm periods, according to
the researchers.
The new atmospheric and climate records from the ice core also
indicate that the response of the natural carbon cycle to climate
warming remains the same over time, explained the researchers.
The new ice core analysis provides insights on our present
interglacial warm period through a glimpse into Antarctic climate and
greenhouse gas concentrations during the most recent warm period that
is relatively similar to our current warm period. Known as Marine
Isotope Stage 11 or MIS 11, this analog warm period occurred between
420,000 and 400,000 years ago.
The similarities between our current warm period and MIS 11 are
primarily due to a similar configuration of the orbits of the Earth
around the Sun: the relative positions of the Earth and Sun are
thought to be the key driver of ice age cycles.
"MIS 11 shows us that the climate system can indeed reside in a
warm period for 20,000 or 30,000 years, something that we can't say
based on the last three warm phases which are no longer than about
10,000 years each," said Stocker.
The greenhouse gas record also provides indirect evidence for
abrupt climate change in the past, the researchers found. This
suggests that abrupt climatic events on time scales relevant to
societies may be common features of the last climatic cycles.
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