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Long debate ended over cause, demise of ice ages (Forwarded)



 
 
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Old August 18th 09, 06:51 PM posted to sci.space.news
Andrew Yee[_1_]
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Default Long debate ended over cause, demise of ice ages (Forwarded)

News and Communications
Oregon State University

Media Contact:
David Stauth, 541-737-0787

Source:
Peter Clark, 541-737-1247

Media Release: 8-6-09

Long debate ended over cause, demise of ice ages -- may also help predict
future

CORVALLIS, Ore. -- A team of researchers says it has largely put to rest a
long debate on the underlying mechanism that has caused periodic ice ages on
Earth for the past 2.5 million years -- they are ultimately linked to slight
shifts in solar radiation caused by predictable changes in Earth's rotation
and axis.

In a publication to be released Friday in the journal Science, researchers
from Oregon State University and other institutions conclude that the known
wobbles in Earth's rotation caused global ice levels to reach their peak
about 26,000 years ago, stabilize for 7,000 years and then begin melting
19,000 years ago, eventually bringing to an end the last ice age.

The melting was first caused by more solar radiation, not changes in carbon
dioxide levels or ocean temperatures, as some scientists have suggested in
recent years.

"Solar radiation was the trigger that started the ice melting, that's now
pretty certain," said Peter Clark, a professor of geosciences at OSU. "There
were also changes in atmospheric carbon dioxide levels and ocean
circulation, but those happened later and amplified a process that had
already begun."

The findings are important, the scientists said, because they will give
researchers a more precise understanding of how ice sheets melt in response
to radiative forcing mechanisms. And even though the changes that occurred
19,000 years ago were due to increased solar radiation, that amount of
heating can be translated into what is expected from current increases in
greenhouse gas levels, and help scientists more accurately project how
Earth's existing ice sheets will react in the future.

"We now know with much more certainty how ancient ice sheets responded to
solar radiation, and that will be very useful in better understanding what
the future holds," Clark said. "It's good to get this pinned down."

The researchers used an analysis of 6,000 dates and locations of ice sheets
to define, with a high level of accuracy, when they started to melt. In
doing this, they confirmed a theory that was first developed more than 50
years ago that pointed to small but definable changes in Earth's rotation as
the trigger for ice ages.

"We can calculate changes in the Earth's axis and rotation that go back 50
million years," Clark said. "These are caused primarily by the gravitational
influences of the larger planets, such as Jupiter and Saturn, which pull and
tug on the Earth in slightly different ways over periods of thousands of
years."

That, in turn, can change the Earth's axis the way it tilts towards the sun
about two degrees over long periods of time, which changes the way sunlight
strikes the planet. And those small shifts in solar radiation were all it
took to cause multiple ice ages during about the past 2.5 million years on
Earth, which reach their extremes every 100,000 years or so.

Sometime around now, scientists say, the Earth should be changing from a
long interglacial period that has lasted the past 10,000 years and shifting
back towards conditions that will ultimately lead to another ice age unless
some other forces stop or slow it. But these are processes that literally
move with glacial slowness, and due to greenhouse gas emissions the Earth
has already warmed as much in about the past 200 years as it ordinarily
might in several thousand years, Clark said.

"One of the biggest concerns right now is how the Greenland and Antarctic
ice sheets will respond to global warming and contribute to sea level rise,"
Clark said. "This study will help us better understand that process, and
improve the validity of our models."

The research was done in collaboration with scientists from the Geological
Survey of Canada, University of Wisconsin, Stockholm University, Harvard
University, the U.S. Geological Survey and University of Ulster. It was
supported by the National Science Foundation and other agencies.

About the OSU College of Science: As one of the largest academic units at
OSU, the College of Science has 14 departments and programs, 13
pre-professional programs, and provides the basic science courses essential
to the education of every OSU student. Its faculty are international leaders
in scientific research.
 




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