Greenhouse Gases Highest For 800,000 Years-Study
NORWAY: May 15, 2008
OSLO - Greenhouse gases are at higher levels in the atmosphere than at any
time in at least 800,000 years, according to a study of Antarctic ice on
Wednesday that extends evidence that mankind is disrupting the climate.
Carbon dioxide and methane trapped in tiny bubbles of air in ancient ice
down to 3,200 metres (10,500 ft) below the surface of Antarctica add 150,000
years of data to climate records stretching back 650,000 years from
shallower ice drilling.
"We can firmly say that today's concentrations of carbon dioxide and methane
are 28 and 124 percent higher respectively than at any time during the last
800,000 years," said Thomas Stocker, an author of the report at the
University of Berne.
Before the Industrial Revolution, levels of greenhouse gases were guided
mainly by long-term shifts in the earth's orbit around the sun that have
plunged the planet into ice ages and back again eight times in the past
800,000 years.
The UN Climate Panel last year blamed human activities, led by burning of
fossil fuels that release heat-trapping gases, for modern global warming
that may disrupt water and food supplies with ever more droughts, floods and
heatwaves.
"The driving forces now are very much different from the driving forces in
the past when there was only natural variation," Stocker told Reuters of the
study in the journal Nature by scientists in Switzerland, France and
Germany.
The experts, working on the European Project for Ice Coring in Antarctica,
drilled down almost to bedrock in Antarctica. They recovered layers of ice
formed by compressed snow, which can be counted much like the rings on
trees.
DEEPER ICE
Stocker said Chinese and Australian scientists were examining possibilities
for drilling in parts of Antarctica with even deeper ice, in some places
4,500 metres thick, that could yield atmospheric records dating back 1.5
million years.
The study also found big natural shifts in carbon dioxide levels. "We find
very conspicuous natural oscillations of carbon dioxide 770,000 years ago
that bear the fingerprint of abrupt climate change during ice ages," Stocker
said.
And the Nature report also set a new record low for carbon dioxide at 172
parts per million (ppm) in the atmosphere about 667,000 years ago, about 10
ppm below the previous known low and giving an ancient natural range of 172
to about 300 ppm.
The study suggested that the low might be a sign that the oceans once soaked
up more carbon dioxide. Carbon dioxide levels are now at about 380 ppm.
Taken together, the data "allow us to learn more eventually about the carbon
cycle and its responses to climate change."
Temperatures in an ice age are about 5-6 Celsius (9 to 11 Fahrenheit) colder
than now, already a mild period in earth's history. Climate change could add
a "best guess" of 1.8 to 4.0 Celsius this century, according to the UN
panel.
The study also linked variations in methane to monsoons.
"The variations of methane concentration point to a strengthening of the
monsoon system in the tropics in the most recent 400,000 years. These
monsoon cycles have become stronger in the second half of this long time
period," Stocker said.
Story by Alister Doyle
REUTERS NEWS SERVICE
|