Human warming hobbles planet
2008-04-27 18:21
Washington - Before humans began
burning fossil fuels, there was an eons-long balance between
carbon dioxide emissions and Earth's ability to absorb them,
but now the planet can't keep up, scientists said on Sunday.
The finding, reported in the journal Nature Geoscience,
relies on ancient Antarctic ice bubbles that contain air
samples going back 610 000 years.
Climate scientists for the last 25 years or so have
suggested that some kind of natural mechanism regulates our
planet's temperature and the level of carbon dioxide in the
atmosphere. Those sceptical about human influence on global
warming point to this as the cause for recent climate change.
This research is likely the first observable evidence for
this natural mechanism.
This mechanism, known as "feedback," has been thrown out of
whack by a steep rise in carbon dioxide emissions from the
burning of coal and petroleum for the last 200 years or so,
said Richard Zeebe, a co-author of the report.
"These feedbacks operate so slowly that they will not help
us in terms of climate change ... that we're going to see in
the next several hundred years," Zeebe said by telephone from
the University of Hawaii. "Right now we have put the system
entirely out of equilibrium."
In the ancient past, excess carbon dioxide came mostly from
volcanoes, which spewed very little of the chemical compared to
what humans activities do now, but it still had to be
addressed.
This antique excess carbon dioxide - a powerful greenhouse
gas - was removed from the atmosphere through the weathering
of mountains, which take in the chemical. In the end, it was
washed downhill into oceans and buried in deep sea sediments,
Zeebe said.
Faster than nature
Zeebe analysed carbon dioxide that had been captured in
Antarctic ice, and by figuring out how much carbon dioxide was
in the atmosphere at various points in time, he and his
co-author determined that it waxed and waned along with the
world's temperature.
"When the carbon dioxide was low, the temperature was low,
and we had an ice age," he said. And while Earth's temperature
fell during ice ages and rose during so-called interglacial
periods between them, the planet's mean temperature has been
going slowly down for about 600 000 years.
The average change in the amount of atmospheric carbon
dioxide over the last 600 000 years has been just 22 parts per
million by volume, Zeebe said, which means that 22 molecules of
carbon dioxide were added to, or removed from, every million
molecules of air.
Since the Industrial Revolution began in the 18th century,
ushering in the widespread human use of fossil fuels, the
amount of carbon dioxide in the atmosphere has risen by 100
parts per million.
That means human activities are putting carbon dioxide into
the atmosphere about 14 000 times as fast as natural processes
do, Zeebe said.
And it appears to be speeding up: the US government
reported last week that in 2007 alone, atmospheric carbon
dioxide increased by 2.4 parts per million.
The natural mechanism will eventually absorb the excess
carbon dioxide, Zeebe said, but not for hundreds of thousands
of years.
"This is a time period that we can hardly imagine," he
said. "They are way too slow to help us to restore the balance
that we have now basically distorted in a very short period of
time."