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<div class="">May 10, 2013</div>
<h1>Heat-Trapping Gas Passes Milestone, Raising Fears </h1>
<h6 class="">By
<span>
<a href="http://topics.nytimes.com/top/reference/timestopics/people/g/justin_gillis/index.html" rel="author" title="More Articles by JUSTIN GILLIS"><span>JUSTIN GILLIS</span></a></span></h6>
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<p>
The level of the most important heat-trapping gas in the atmosphere,
carbon dioxide, has passed a long-feared milestone, scientists reported
Friday, reaching a concentration not seen on the earth for millions of
years. </p>
<p>
Scientific instruments showed that the gas had reached an average daily
level above 400 parts per million — just an odometer moment in one
sense, but also a sobering reminder that decades of efforts to bring
human-produced emissions under control are faltering. </p>
<p>
The best available evidence suggests the amount of the gas in the air
has not been this high for at least three million years, before humans
evolved, and scientists believe the rise portends large changes in the
climate and the level of the sea. </p>
<p>
“It symbolizes that so far we have failed miserably in tackling this
problem,” said Pieter P. Tans, who runs the monitoring program at the
National Oceanic and Atmospheric Administration that reported the new
reading. </p>
<p>
Ralph Keeling, who runs another monitoring program at the <a href="http://scrippsco2.ucsd.edu/">Scripps Institution of Oceanography</a>
in San Diego, said a continuing rise could be catastrophic. “It means
we are quickly losing the possibility of keeping the climate below what
people thought were possibly tolerable thresholds,” he said. </p>
<p>
Virtually every automobile ride, every plane trip and, in most places,
every flip of a light switch adds carbon dioxide to the air, and
relatively little money is being spent to find and deploy alternative
technologies. </p>
<p>
China is now the largest emitter, but Americans have been consuming
fossil fuels extensively for far longer, and experts say the United
States is more responsible than any other nation for the high level.
</p>
<p>
The new measurement came from <a title="Times article" href="http://www.nytimes.com/2010/12/22/science/earth/22carbon.html?pagewanted=all&_r=0">analyzers atop Mauna Loa</a>,
the volcano on the big island of Hawaii that has long been ground zero
for monitoring the worldwide trend on carbon dioxide, or CO2. <a href="http://www.esrl.noaa.gov/gmd/ccgg/trends/weekly.html">Devices there sample</a>
clean, crisp air that has blown thousands of miles across the Pacific
Ocean, producing a record of rising carbon dioxide levels that has been
closely tracked for half a century. </p>
<p>
Carbon dioxide above 400 parts per million was first seen in the Arctic
last year, and had also spiked above that level in hourly readings at
Mauna Loa. </p>
<p>
But the average reading for an entire day surpassed that level at Mauna
Loa for the first time in the 24 hours that ended at 8 p.m. Eastern
Daylight Time on Thursday. The two monitoring programs use slightly
different protocols; NOAA reported an average for the period of 400.03
parts per million, while Scripps reported 400.08. </p>
<p>
Carbon dioxide rises and falls on a seasonal cycle, and the level will
dip below 400 this summer as leaf growth in the Northern Hemisphere
pulls about 10 billion tons of carbon out of the air. But experts say
that will be a brief reprieve — the moment is approaching when no
measurement of the ambient air anywhere on earth, in any season, will
produce a reading below 400. </p>
<p>
“It feels like the inevitable march toward disaster,” said Maureen E.
Raymo, a scientist at the Lamont-Doherty Earth Observatory, a unit of
Columbia University. </p>
<p>
>From studying air bubbles trapped in Antarctic ice, scientists know that
going back 800,000 years, the carbon dioxide level oscillated in a
tight band, from about 180 parts per million in the depths of ice ages
to about 280 during the warm periods between. The evidence shows that
global temperatures and CO<sub>2</sub> levels are tightly linked. </p>
<p>
For the entire period of human civilization, roughly 8,000 years, the
carbon dioxide level was relatively stable near that upper bound. But
the burning of fossil fuels has caused a 41 percent increase in the
heat-trapping gas since the Industrial Revolution, a mere geological
instant, and scientists say the climate is beginning to react, though
they expect far larger changes in the future. </p>
<p>
Indirect measurements suggest that the last time the carbon dioxide
level was this high was at least three million years ago, during an
epoch called the Pliocene. Geological research shows that the climate
then was far warmer than today, the world’s ice caps were smaller, and
the sea level might have been as much as 60 or 80 feet higher. </p>
<p>
Experts fear that humanity may be precipitating a return to such
conditions — except this time, billions of people are in harm’s way.
</p>
<p>
“It takes a long time to melt ice, but we’re doing it,” Dr. Keeling said. “It’s scary.” </p>
<p>
Dr. Keeling’s father, Charles David Keeling, began carbon dioxide
measurements on Mauna Loa and at other locations in the late 1950s. The
elder Dr. Keeling found a level in the air then of about 315 parts per
million — meaning that if a person had filled a million quart jars with
air, about 315 quart jars of carbon dioxide would have been mixed in.
</p>
<p>
His analysis revealed a relentless, long-term increase superimposed on the seasonal cycle, a trend that was dubbed the <a title="Background on the Keeling Curve" href="http://scrippsco2.ucsd.edu/">Keeling Curve</a>. </p>
<p>
Countries have adopted an official target to limit the damage from
global warming, with 450 parts per million seen as the maximum level
compatible with that goal. “Unless things slow down, we’ll probably get
there in well under 25 years,” Ralph Keeling said. </p>
<p>
Yet many countries, including China and the United States, have refused
to adopt binding national targets. Scientists say that unless far
greater efforts are made soon, the goal of limiting the warming will
become impossible without severe economic disruption. </p>
<p>
“If you start turning the Titanic long before you hit the iceberg, you
can go clear without even spilling a drink of a passenger on deck,” said
Richard B. Alley, a climate scientist at Pennsylvania State University.
“If you wait until you’re really close, spilling a lot of drinks is the
best you can hope for.” </p>
<p>
Climate-change contrarians, who have little scientific credibility but
are politically influential in Washington, point out that carbon dioxide
represents only a tiny fraction of the air — as of Thursday’s reading,
exactly 0.04 percent. “The CO<sub>2</sub> levels in the atmosphere are
rather undramatic,” a Republican congressman from California, Dana
Rohrabacher, said in a Congressional hearing several years ago. </p>
<p>
But climate scientists reject that argument, saying it is like claiming
that a tiny bit of arsenic or cobra venom cannot have much effect.
Research shows that even at such low levels, carbon dioxide is potent at
trapping heat near the surface of the earth. </p>
<p>
“If you’re looking to stave off climate perturbations that I don’t
believe our culture is ready to adapt to, then significant reductions in
CO<sub>2</sub> emissions have to occur right away,” said Mark Pagani, a
Yale geochemist who studies climates of the past. “I feel like the time
to do something was yesterday.” </p></div>
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