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http://www.washingtonpost.com/wp-dyn/content/article/2006/01/28/AR2006012801021_pf.html

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


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."