❍ LexisNexis(TM)
Academic - Document Home | Sources
| How
Do I? | Site
Map | What's
New | Help
Search Terms: tipping point
Copyright
2006 The
'Tipping Point' When It Is Too Late to
Act BYLINE: Juliet
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
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."
While both the
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
Many scientists are also worried about a
possible collapse of the Atlantic thermohaline circulation, a current that
brings warm surface water to northern
Some scientists, including President Bush's
chief science adviser, John H. Marburger III, emphasize there is still much
uncertainty about when abrupt global warming
"There's no agreement on what it is that
constitutes a dangerous climate change," said Marburger, adding that the
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
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
"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.
David Warrilow, who heads science policy on
climate change for
"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
"For
LOAD-DATE:
Terms and
Conditions | Privacy
Copyright
© 2006 LexisNexis, a
division of Reed Elsevier Inc. All Rights Reserved.