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SCIENCE-FOR-THE-PEOPLE  November 2005

SCIENCE-FOR-THE-PEOPLE November 2005

Subject:

Core Evidence That Humans Affect Climate Change

From:

"S. E. Anderson" <[log in to unmask]>

Reply-To:

Science for the People Discussion List <[log in to unmask]>

Date:

Sat, 26 Nov 2005 05:00:32 -0800

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (139 lines)

Core Evidence That Humans Affect Climate Change:
Ice drilled in Antarctica offers the fullest record of
glacial cycles and greenhouse gas levels.

By Usha Lee McFarling, Times Staff Writer
Los Angeles Times - November 25, 2005

http://www.latimes.com/news/nationworld/nation/la-na-ice25nov25,0,2141135.story?coll=la-home-headlines

An ice core about two miles long - the oldest frozen
sample ever drilled from the underbelly of Antarctica -
shows that at no time in the last 650,000 years have
levels of the greenhouse gases carbon dioxide and
methane been as high as they are today.

The research, published in today's issue of the journal
Science, describes the content of the greenhouse gases
within the core and shows that carbon dioxide levels
today are 27% higher than they have been in the last
650,000 years and levels of methane, an even more
powerful greenhouse gas, are 130% higher, said Thomas
Stocker, a climate researcher at the University of Bern
and senior member of the European team that wrote two
papers based on the core.

ADVERTISEMENT The work provides more evidence that
human activity since the Industrial Revolution has
significantly altered the planet's climate system,
scientists said. "This is saying, 'Yeah, we had it
right.' We can pound on the table harder and say, 'This
is real,' " said Richard Alley, a Penn State University
geophysicist and expert on ice cores who was not
involved with the analysis.

Previous records, from an ice core drilled at the
Russian Antarctic station Vostok, extended back 440,000
years. Extracting and analyzing that core was a major
achievement, but the core stopped short of a time
period scientists are anxious to study because it was
like today's.

Climate scientists called the analysis of the older
records spectacular because they were so clear and said
they would become "canonical" additions to the climate
record. "It's really important," Ed Brook, an ice core
expert at Oregon State University said of the new
research. "Those 200,000 years were a lot harder to get
than the previous 400,000 - and those were hard
enough."

Ice cores are plugs drilled from glaciers and ice
sheets. They are composed of tens of thousands of
layers of fallen snow and air bubbles compressed over
time. Ice cores are among the most powerful tools
available to climate scientists. The chemistry of the
ice reveals temperatures from the distant past, while
bubbles within the ice are minuscule time capsules that
capture air and greenhouse gases as they existed
hundreds of thousands of years ago.

The ice core was drilled by the European Project for
Ice Coring in Antarctica from a high plateau in East
Antarctica called Dome C that rises about two miles
above sea level. It is one of the driest, coldest parts
of the continent, where summer temperatures can fall to
50 degrees below zero. Temperature records from the
core were published in 2004, and scientists have been
waiting for an analysis of the core's gases.

The last time carbon dioxide levels were as high or
higher than today was probably tens of millions of
years ago, Alley said. Over millions of years, carbon
dioxide levels shift because of slow geological
processes, such as weathering of rocks, swallowing of
crust into subduction zones and the release of gases
from volcanoes. But these processes are much slower and
more gradual than the current rapid increase of carbon
dioxide into the atmosphere from the burning of fossil
fuels, Alley said.

Scientists are enthusiastic about the ice core because
it includes about eight full glacial cycles. The Vostok
sample had four. Glacial cycles occur roughly every
100,000 years and include long periods of cold, when
ice ages occur, and brief, warm interglacial periods,
such as the current one. The cycles are controlled by
shakes, wobbles and tilts in the Earth's orbit around
the sun that determine the amount of sunlight falling
on and warming the planet.

The Vostok core showed that warm interglacial periods
lasted about 10,000 years. Because the current
temperate interglacial period has lasted about 12,000
years, many scientists had speculated that the planet
was overdue for an ice age.

But the new core shows that the interglacial period of
440,000 years ago, when the Earth's position relative
to the sun was similar to what it is today, lasted
nearly 30,000 years and was not ended by natural
decreases in carbon dioxide, Stocker said. The work
suggests that the next ice age is about 15,000 years
away.

"Anyone counting on an ice age to head off global
warming, or hoping to justify human greenhouse-gas
emissions as a useful attempt to head off the next ice
age, will find no comfort in the ice-core record,"
Alley said.

The latest findings also run counter to a theory
presented two years ago by William Ruddiman, a
professor emeritus of environmental sciences at the
University of Virginia, that humans who lived five
thousand or more years ago are responsible for delaying
the next ice age because their activities - forest
clearing and rice growing - started to raise greenhouse
gas levels when they should have been naturally
declining.

"This claim can no longer be upheld," said Stocker,
because the ice core shows greenhouse gases do not
naturally decline after 10,000 years in the longer
interglacial periods like today's.

Scientists are eager to look further back into earth's
climatic past. About a million years ago, the earth
shifted from ice age cycles that were 40,000 years long
into cycles that were 100,000 years long. This shift
from a "40K world to a 100K world" is a major mystery,
said Oregon State's Brook, and will require a core that
reaches deeper into the ice and much further back in
time.

Brook is co-chairman of a joint European and American
group that hopes to start drilling in coming years a
core that could produce ice and bubbles that are 1.2
million to 1.5 million years old.

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