Abrupt Climate Shifts May Come Sooner, Not Later

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“Many scientists are now raising the possibility
that abrupt, catastrophic switches in natural
systems may punctuate the steady rise in global
temperatures now underway.”

“In the interior United States, a widespread
drought that began in the Southwest about 6 years
ago could be the leading edge of a new climate
regime for a wider region.”

“[There is an] urgent need for committed and
sustained monitoring of those components [that]
are particularly vulnerable.”
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Earth Institute News
Jeffrey Sachs, Director
2008-12-19

Abrupt Climate Shifts May Come Sooner, Not Later
Rising Seas, Severe Drought, Could Come in Decades, Says U.S. Report

To get the full report, go here:
http://www.climatescience.gov/Library/sap/sap3-4/final-report/default.htm.

San Francisco– The United States could suffer
the effects of abrupt climate changes within
decades-sooner than some previously thought–says
a new government report. It contends that seas
could rise rapidly if melting of polar ice
continues to outrun recent projections, and that
an ongoing drought in the U.S. west could be the
start of permanent drying for the region.
Commissioned by the U.S. Climate Change Science
Program, the report was authored by experts from
the U.S. Geological Survey, Columbia University’s
Lamont-Doherty Earth Observatory and other
leading institutions. It was released at this
week’s meeting of the American Geophysical Union.


Many scientists are now raising the possibility
that abrupt, catastrophic switches in natural
systems may punctuate the steady rise in global
temperatures now underway. However, the
likelihood and timing of such “tipping points,”
where large systems move into radically new
states, has been controversial.  The new report
synthesizes the latest published evidence on four
specific threats for the 21st century. It uses
studies not available to the Intergovernmental
Panel on Climate Change (IPCC), whose widely
cited 2007 report explored similar questions.
“This is the most up to date, as it includes
research that came out after IPCC assembled its
data,” said Edward Cook, a climatologist at
Lamont-Doherty and a lead author of the new study.

The researchers say the IPCC’s maximum estimate
of two feet of sea level rise by 2100 may be
exceeded, because new data shows that melting of
polar ice sheets is accelerating. Among other
things, there is now good evidence that the
Antarctic ice cap is losing overall mass. At the
time of the IPCC report, scientists were
uncertain whether collapses of ice shelves into
the ocean off the western Antarctica were being
offset by snow accumulation in the continent’s
interior. But one coauthor, remote-sensing
specialist Eric Rignot of the Jet Propulsion
Laboratory, told a press conference at the
meeting:  “There is a new consensus that
Antarctica is losing mass.” Seaward flow of ice
from Greenland is also accelerating. However,
projections of how far sea levels might rise are
“highly uncertain,” says the report, as
researchers cannot say whether such losses will
continue at the same rates.

In the interior United States, a widespread
drought that began in the Southwest about 6 years
ago could be the leading edge of a new climate
regime for a wider region. Cook, who heads
Lamont’s Tree Ring Lab, says that periodic
droughts over the past 1,000 years have been
driven by natural cycles in air circulation, and
that these cycles appear to be made more intense
and persistent by warming. Among the new research
cited is a 2007 Science paper by Lamont climate
modeler Richard Seager, showing how changes in
temperature over the Pacific have driven
large-scale droughts across western North
America. “We have no smoking gun saying that
humans are causing the current changes. But the
past is a cautionary tale,” Cook told the press
conference. “What this tells us is that the
system has the ability to lock into periods of
profound, long-lasting aridity. And there is the
suggestion that these changes are related to
warmer climate.” Cook added: “If the system tips
over, that would have catastrophic effects no
human activities and populations over wide areas.”

The panel said two other systemic changes seem
less imminent, but are still of concern. Vast
quantities of methane, a potent greenhouse gas,
have long been locked up in ocean sediments,
wetlands and permafrost. These could be
destabilized by climate change, leading to
blowouts of gas, and thus even more abrupt
temperature shifts. The panel said blowouts
appear unlikely in the next 100 years-but that
steady emissions could double, especially in the
north, as land and water warm up. The panel also
looked at the continuous circulation of the
Atlantic Ocean, which sends warm water northward
and cold water southward, controlling the climate
of western Europe and beyond. Some scientists say
this circulation could collapse if enough
northern ice melts and dilutes the salty water.
The panel found this scenario unlikely in the
short term, but warned that the circulation’s
strength might decline 25% to 30% by 2100.

“Abrupt climate change presents potential risks
for society that are poorly understood,” the
researchers write. [There is an] urgent need for
committed and sustained monitoring of those
components [that] are particularly vulnerable.”

The report, Synthesis and Assessment Product 3.4:
Abrupt Climate Change, is at:
http://www.climatescience.gov/Library/sap/sap3-4/final-report/default.htm.

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