[Mb-civic] Tipping Point

[ean at sbcglobal.net]

Debate on Climate Shifts to Issue of Irreparable Change
Some Experts on Global Warming Foresee 'Tipping Point'
When It Is Too Late to Act

By Juliet Eilperin
Washington Post Staff Writer
Sunday, January 29, 2006; A01
http://www.washingtonpost.com/wp-
dyn/content/article/2006/01/28/AR20060128
01021_pf.html

Now that most scientists agree human activity is
causing Earth to warm, the central debate has shifted
to whether climate change is progressing so rapidly
that, within decades, humans may be helpless to slow or
reverse the trend.

This "tipping point" scenario has begun to consume many
prominent researchers in the United States and abroad,
because the answer could determine how drastically
countries need to reduce their greenhouse gas emissions
in the coming years. While scientists remain uncertain
when such a point might occur, many say it is urgent
that policymakers cut global carbon dioxide emissions
in half over the next 50 years or risk the triggering
of changes that would be irreversible.

There are three specific events that these scientists
describe as especially worrisome and potentially
imminent, although the time frames are a matter of
dispute: widespread coral bleaching that could damage
the world's fisheries within three decades; dramatic
sea level rise by the end of the century that would
take tens of thousands of years to reverse; and, within
200 years, a shutdown of the ocean current that
moderates temperatures in northern Europe.

The debate has been intensifying because Earth is
warming much faster than some researchers had
predicted. James E. Hansen, who directs NASA's Goddard
Institute of Space Studies, last week confirmed that
2005 was the warmest year on record, surpassing 1998.
Earth's average temperature has risen nearly 1 degree
Fahrenheit over the past 30 years, he noted, and
another increase of about 4 degrees over the next
century would "imply changes that constitute
practically a different planet."

"It's not something you can adapt to," Hansen said in
an interview. "We can't let it go on another 10 years
like this. We've got to do something."

Princeton University geosciences and international
affairs professor Michael Oppenheimer, who also advises
the advocacy group Environmental Defense, said one of
the greatest dangers lies in the disintegration of the
Greenland or West Antarctic ice sheets, which together
hold about 20 percent of the fresh water on the planet.
If either of the two sheets disintegrates, sea level
could rise nearly 20 feet in the course of a couple of
centuries, swamping the southern third of Florida and
Manhattan up to the middle of Greenwich Village.

While both the Greenland and the Antarctic ice sheets
as a whole are gaining some mass in their cold
interiors because of increasing snowfall, they are
losing ice along their peripheries. That indicates that
scientists may have underestimated the rate of
disintegration they face in the future, Oppenheimer
said. Greenland's current net ice loss is equivalent to
an annual 0.008 inch sea level rise.

The effects of the collapse of either ice sheet would
be "huge," Oppenheimer said. "Once you lost one of
these ice sheets, there's really no putting it back for
thousands of years, if ever."

Last year, the British government sponsored a
scientific symposium on "Avoiding Dangerous Climate
Change," which examined a number of possible tipping
points. A book based on that conference, due to be
published Tuesday, suggests that disintegration of the
two ice sheets becomes more likely if average
temperatures rise by more than 5 degrees Fahrenheit, a
prospect "well within the range of climate change
projections for this century."

The report concludes that a temperature rise of just
1.8 degrees Fahrenheit "is likely to lead to extensive
coral bleaching," destroying critical fish nurseries in
the Caribbean and Southeast Asia. Too-warm sea
temperatures stress corals, causing them to expel
symbiotic micro-algae that live in their tissues and
provide them with food, and thus making the reefs
appear bleached. Bleaching that lasts longer than a
week can kill corals. This fall there was widespread
bleaching from Texas to Trinidad that killed broad
swaths of corals, in part because ocean temperatures
were 2 degrees Fahrenheit above average monthly
maximums.

Many scientists are also worried about a possible
collapse of the Atlantic thermohaline circulation, a
current that brings warm surface water to northern
Europe and returns cold, deep-ocean water south. Hans
Joachim Schellnhuber, who directs Germany's Potsdam
Institute for Climate Impact Research, has run multiple
computer models to determine when climate change could
disrupt this "conveyor belt," which, according to one
study, is already slower than it was 30 years ago.
According to these simulations, there is a 50 percent
chance the current will collapse within 200 years.

Some scientists, including President Bush's chief
science adviser, John H. Marburger III, emphasize there
is still much uncertainty about when abrupt global
warming might occur.

"There's no agreement on what it is that constitutes a
dangerous climate change," said Marburger, adding that
the U.S. government spends $2 billion a year on
researching this and other climate change questions.
"We know things like this are possible, but we don't
have enough information to quantify the level of risk."

This tipping point debate has stirred controversy
within the administration; Hansen said senior political
appointees are trying to block him from sharing his
views publicly.

When Hansen posted data on the Internet in the fall
suggesting that 2005 could be the warmest year on
record, NASA officials ordered Hansen to withdraw the
information because he had not had it screened by the
administration in advance, according to a Goddard
scientist who spoke on the condition of anonymity. More
recently, NASA officials tried to discourage a reporter
from interviewing Hansen for this article and later
insisted he could speak on the record only if an agency
spokeswoman listened in on the conversation.

"They're trying to control what's getting out to the
public," Hansen said, adding that many of his
colleagues are afraid to talk about the issue. "They're
not willing to say much, because they've been pressured
and they're afraid they'll get into trouble."

But Mary L. Cleave, deputy associate administrator for
NASA's Office of Earth Science, said the agency insists
on monitoring interviews with scientists to ensure they
are not misquoted.

"People could see it as a constraint," Cleave said. "As
a manager, I might see it as protection."

John R. Christy, director of the Earth Science System
Center at the University of Alabama in Huntsville, said
it is possible increased warming will be offset by
other factors, such as increased cloudiness that would
reflect more sunlight. "Whatever happens, we will adapt
to it," Christy said.

Scientists who read the history of Earth's climate in
ancient sediments, ice cores and fossils find clear
signs that it has shifted abruptly in the past on a
scale that could prove disastrous for modern society.
Peter B. deMenocal, an associate professor at the
Lamont-Doherty Earth Observatory of Columbia
University, said that about 8,200 years ago, a very
sudden cooling shut down the Atlantic conveyor belt. As
a result, the land temperature in Greenland dropped
more than 9 degrees Fahrenheit within a decade or two.

"It's not this abstract notion that happens over
millions of years," deMenocal said. "The magnitude of
what we're talking about greatly, greatly exceeds
anything we've withstood in human history."

These kinds of concerns have spurred some governments
to make major cuts in the carbon dioxide emissions
linked to global warming. Britain has slashed its
emissions by 14 percent, compared with 1990 levels, and
aims to reduce them by 60 percent by 2050. Some
European countries, however, are lagging well behind
their targets under the international Kyoto climate
treaty.

David Warrilow, who heads science policy on climate
change for Britain's Department of Environment, Food
and Rural Affairs, said that while the science remains
unsettled, his government has decided to take a
precautionary approach. He compared consuming massive
amounts of fossil fuels to the strategy of the
Titanic's crew, who were unable to avoid an iceberg
because they were speeding across the Atlantic in hopes
of breaking a record.

"We know there are icebergs out there, but at the
moment we're accelerating toward the tipping point,"
Warrilow said in an interview. "This is silly. We
should be doing the opposite, slowing down whilst we
build up our knowledge base."

The Bush administration espouses a different approach.
Marburger said that though everyone agrees carbon
dioxide emissions should decline, the United States
prefers to promote cleaner technology rather than
impose mandatory greenhouse gas limits. "The U.S. is
the world leader in doing something on climate change
because of its actions on changing technology," he
said.

Stanford University climatologist Stephen H. Schneider,
who is helping oversee a major international assessment
of how climate change could expose humans and the
environment to new vulnerabilities, said countries
respond differently to the global warming issue in part
because they are affected differently by it. The small
island nation of Kiribati is made up of 33 small
atolls, none of which is more than 6.5 feet above the
South Pacific, and it is only a matter of time before
the entire country is submerged by the rising sea.

"For Kiribati, the tipping point has already occurred,"
Schneider said. "As far as they're concerned, it's
tipped, but they have no economic clout in the world."

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"A war of aggression is the supreme international crime." -- Robert Jackson,
 former U.S. Supreme Court Chief Justice and Nuremberg prosecutor

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