http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/7363600.stm
2008/04/28 Nature’s carbon balance confirmed
Scientists have found new evidence that the Earth’s
natural feedback mechanism regulated carbon dioxide
levels for hundreds of thousands of years. But they say
humans are now emitting CO2 so fast thatthe planet’s
natural balancing mechanism cannot keep up.
The researchers, writing in the journal Nature
Geoscience, say their findings confirm a long-believed
theory.
Carbon spewed out by volcanoes is removed from the air
by rock weathering and transported to the ocean floor.
Using evidence from an Antarctic ice core, the team
calculated that over a period of 610,000 years the
long-term change in atmospheric CO2 concentration was
just 22 parts per million (ppm), although there were
larger fluctuations associated with the transitions
between glacial and interglacial conditions.
By comparison, two centuries of human industry have
raised levels by about 100 ppm – a speed of rise about
14,000 times faster.
“These long term cycles are way too slow to protect us
from the effect of (anthropogenic) greenhouse gases,”
said Richard Zeebe from the University of Hawaii in
Honolulu.
“They will not help us with our current CO2 problem.
Right now, we have put the system entirely out of
equilibrium.”
Deep level
Scientists have long believed that the Earth’s climate
was stabilised by a natural carbon thermostat.
In their model, carbon released into the atmosphere,
primarily by volcanoes, is slowly removed through the
weathering of mountains, washed downhill into oceans,
and finally buried in deep sea sediments.
“A lot of people had tried to refute this hypothesis,
but our study provides the first direct evidence (that
it is correct),” said Dr Zeebe.
He studied levels of CO2 recorded in air bubbles
trapped in a 3km ice core drilled from an Antarctic
region called Dome Concordia (Dome C).Data from the
ice core, drilled by the EuropeanProject for Ice
Coring in Antarctica (Epica), wasfirst published in 2005.
But rather than focusing on the peaks and troughs of
CO2 – as other researchers have done – this group
looked at the long term trend, and compared the ice
core data with records of carbonate saturation in the
deep sea for the last six glacial cycles.
“It is remarkable how exact the balance is between the
carbon input from volcanoes and the output from rock
weathering,” said Dr Zeebe. “This suggests a natural
thermostat which helps maintain climate stability.”
The delicately balanced carbon thermostat has been a
key factor in allowing liquid water, and life, to
remain on Earth, he said.
“If it weren’t for these feedbacks, the Earth would
look very different today.”
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