the first treaty addressing global warming, 193 countries,
including the United States, pledged to avoid "dangerous"
human interference with the climate.
There was one small problem with that treaty, enacted 11
years ago. No one defined dangerous. With no clear goal,
smokestack and tailpipe emissions of gases linked to rising
temperatures relentlessly climbed.
On Feb. 16, a stricter addendum to that treaty, the Kyoto
Protocol, enters into force, requiring participating
industrialized countries to cut such emissions.
But its targets and timetable were negotiated with no
agreement on what amount of cuts would lead the world toward
climatic stability. The arbitrary terms were cited by
President Bush when he rejected the Kyoto pact in 2001,
leaving the world's biggest source of such gases on the
After a decade of cautious circling, some scientists and
policy makers are now trying to agree on how much warming is
One possible step toward clarity comes today, as 200
experts from around the world meet at the invitation of Prime
Minister Tony Blair in Exeter for three days of talks on
defining "dangerous climate change" and how to avoid it.
The researcher running the meeting, Dennis A. Tirpak,
formerly of the Environmental Protection Agency, said that
experts always realized it would take a long time for
science's projections to be absorbed by society, but few
thought it would take this long.
"I've always been a believer that science and truth will
win out in the end," he said. "But I have a sense we might be
running out of time."
It has taken this long not just because the "dangerous"
question is complicated, but because it holds dangers in and
of itself. If scientists offer answers, as some have in recent
days, they can be criticized for playing down uncertainties
and intruding into the policy arena. If a politician answers,
that creates a yardstick for measuring later progress or
It is much easier for everyone simply to call for more
But some experts now say that by the time clear evidence is
at hand, calamity later in the century will be unavoidable.
They say fresh findings show that potentially enormous
environmental changes lie ahead.
"I think that the scientific evidence now warrants a new
sense of urgency," said Dr. James E. Hansen, a climate
scientist and director of NASA's Goddard Institute for Space
A particular concern is the Arctic. An eight-nation,
four-year study concluded in November that accumulating carbon
dioxide and other emissions from human activities were
contributing to the thawing of tundra and the retreat of sea
ice. Recent studies of accelerating flows of ice to the sea in
some parts of Antarctica also point to the prospect of a
quickening rise in sea levels in a warming world. Other
scientists point to the prospect of intensified droughts and
With pressure building for resolution and fresh action,
some countries and groups of experts have tried to define a
specific rise in earth's average temperature that presents
The European Union has set this threshold at 2.5 degrees of
additional warming from current conditions. That was also the
danger level chosen last week by an international task force
of scientists, policy experts, business leaders and elected
officials led by Senator Olympia J. Snowe, Republican of
Maine, and Stephen Byers, a Labor Party member of the British
Some scientists have criticized this approach, saying
understanding of the impact of greenhouse gases on the
atmosphere remains far too primitive to manage emissions and
thus avoid a particular temperature target.
Others say the most logical response to the problem is to
make societies more resilient to inherent extremes of climate.
"If we just significantly minimize our vulnerabilities to the
extremes which occurred during the last 250 years, we'll be
O.K. for the next 100," said Dr. John Christy, a climate
scientist at the University of Alabama who has long opposed
cuts in emissions. As for rising seas, he said, "You've got
100 years to move inland."
Dr. Michael Schlesinger, who directs climate research at
the University of Illinois, will contend at the meeting that
the persistent uncertainty itself about big climate perils is
precisely the reason to invest now in modest mandatory curbs
on greenhouse-gas emissions.
Only with such a prod will societies move toward
less-polluting choices, even as research continues on energy
options that could in a few decades sharply reduce the human
contribution to the greenhouse effect.
Without global participation in such emission curbs,
though, the shared atmosphere will essentially remain a dump
with no gate or tipping fee for countries rejecting action.
Any consensus on climate risks will likely intensify
pressure on the Bush administration to shift from its current
opposition to any cuts in the gases.
In a speech Wednesday at the World Economic Forum, Mr.
Blair pressed the United States to join Britain and other
industrialized countries that have agreed to curbs on the
While the risks remained uncertain, Mr. Blair said, "It
would be wrong to say that the evidence of danger is not
clearly and persuasively advocated by a very large number of
entirely independent and compelling voices."
The Exeter meeting will probably set the tone for the next
review of climate trends and causes. In 2007, the
Intergovernmental Panel on Climate Change, a United Nations
body, will issue a report that is expected to be the most
comprehensive summation so far of human understanding of
In three reports to date, that panel has fastidiously
avoided defining unacceptable danger, though it has confirmed
that humans have contributed to recent warming.
Its current chairman, Dr. Rajendra K. Pachauri, an
economist and engineer from India, is to address the
In an interview, he said it was clear that emissions
contributing to warming had to be reduced, but defining what
is dangerous remained a "value judgment" that was
fundamentally the responsibility of society and its elected
He and several other experts said that everyone in the
climate debate, scientists and policy makers, had to get used
to the idea that whatever decisions were made, they would be
made without scientific clarity.
Efforts to imply a false sense of certainty will backfire,
and efforts to use uncertainty as an excuse for doing nothing
will simply raise the stakes as more years slide by, and more
long-lived emissions accumulate in the air.