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Will Global Warming Melt the Permafrost Supporting the China-Tibet Railway?

July 22, 2009

This crucial line of transportation crosses the Tibetan Plateau, parts
of which are barely below freezing. Will any added warmth--either from
climate change or the railway itself--destabilize the track's frozen
foundation?
By Abrahm Lustgarten
Scientific American, July 22, 2009


Building a railway across the unstable soil of the Tibetan Plateau was
an improbable endeavor from the start, but an army of Chinese government
engineers did it anyway.

Now, with the frozen soil disturbed by the process of laying down the
rail and a warming climate on the plateau, some scientists question
whether the $4-billion rail line will survive as is or require major
reconstruction.

Three years after the railway opened in 2006, international research
shows that the Tibetan territories are among the fastest warming, and
fastest melting, on the planet. The research into the fate of glaciers
and the permafrost soils?done by the United Nations, China's scientific
agencies, and several independent scientists?is not focused on the
railway. But the work raises concerns that the warming ground could lead
to a buckling of the railway.

(Im)permafrost
According to a 2007 global outlook from the U.N. Environment Programme
(UNEP), the frozen soil of the Tibetan plateau has warmed about 0.3
degree Celsius over the past 30 years?after the poles, faster than
anywhere else on the planet. Where human activity has disturbed the
soil, such as during the construction of the railway, the rate is
double, 0.6 degree C.

That might not seem like much, but it is enough to outpace the rate
predicted by railway construction engineers for the landmark rail line,
which has carried some six million passengers and five million tons of
cargo since opening day. And the news would seem to get worse: UNEP says
the permafrost area surrounding the nearby Qinghai?Tibet Highway
decreased some 36 percent in size in the 20 years leading up to 1995,
the period for which data were recorded. By the end of this century, the
report says, China's permafrost (which is almost entirely on the Tibetan
plateau) could decrease by half again. By 2050, another U.N. report
predicts, the glaciers on the plateau will have shrunk by one third.

Perhaps that outlook can explain the warning offered by the China
Meteorological Administration at a meeting in the Tibetan capital of
Lhasa in early May that Tibet was warming faster than anywhere else in
China. According to an account published by the Xinhua News Agency,
China's state media service, the administration's chief, Zheng Guoguang,
said that the railway may be in jeopardy and that the region must
"tackle" the effects of climate change. Zheng warned that, where the
railway crosses plateau regions, the thickness of the permafrost had
been decreasing by as much as 25 centimeters each decade.

Melting point
Other research points to the railway itself as a contributing factor. A
2007 paper published by the University of Colorado at Boulder's
Institute of Arctic and Alpine Research indicated that the more
delicate, warm permafrost areas are more affected by the climate warming
because their natural balance has been upset by the construction's
disturbance of the land. Whereas it would take about 20 years for the
warm permafrost regions to thaw under present climate change conditions,
the paper says it could take just five years for that permafrost
underneath the disturbed land to reach the melting point. The study,
published in Arctic, Antarctic, and Alpine Research, was written in part
by Chinese scientists close to the railway project.

That research, however, is general to the region and does not examine
the railway itself. Nor does it account for effectiveness of the methods
that engineers used to cool the soil while they built the tracks.
Methods included using pipes called thermosiphons along the sides of the
tracks to refrigerate vulnerable parts of the soil along the highest
parts of the plateau, an area that comprises the largest continuous
sub-Arctic permafrost region on the planet. These cooling sticks are
7.6-meter-long steel tubes drilled into the soil; they contain ammonia,
which draws latent heat out of the soil as it evaporates. The technique
has been used along the Trans-Alaska Pipeline and in Siberia, although
those projects relied on the cooling sticks to a far lesser extent than
the Tibet project and were built in colder climes.

The skeptic
The railway, which connects Lhasa to the China's national railway
network, the largest in the world, traverses the Tibetan Plateau 5,182
meters above sea level and crosses about 550 kilometers of some of the
most delicate and treacherous frozen soil regions on Earth. Half of the
permafrost beneath the rails is within ?1 degree C, meaning that it
could melt with just a degree of climate change.

Some question whether the engineers who planned the railway made the
proper calculations to account for long-term climate change. The
project's chief engineers counted on cooling sticks and other tricks to
help the rails withstand soil warming of 0.2 degree C and air warming of
2 degrees C on the plateau over the next 50 years. The figures?decided
on in early 2003?were the least conservative, and thus the least
expensive, to accommodate.

In early 2006, as the five-year construction project finally neared
completion, a Chinese Academy of Sciences (CAS) engineer named Wu Ziwang
predicted that the rate of change was more serious, concluding that the
frozen ground supporting the railway could be soaked with puddles within
a decade. A lone voice at the time, the researcher was admonished for
his candor, rebuked by his department, and later declined to be
interviewed for this story when I visited his CAS office in Lanzhou,
located deep in central China.

Out of danger?
Clearly, not everyone believes the railway is in imminent danger.
According to Cheng Guodong, one of the project's master scientists, the
permafrost directly under the rail bed may be thinning, but it is
holding firm, and that bodes well for its ability to withstand further
warming. In his 2006 paper published in the journal Cold Regions Science
and Technology, he wrote, "The temperature of the permafrost under the
duct?decreased remarkably." As a result of this, according to the paper,
the frozen layers have spread upward in some places, freezing the dirt
infill of the rail bed itself.

Guodong explains that the construction impact posed a greater threat to
the plateau permafrost than global warming. "The first two to three
years might be the most dangerous period," he wrote in a translated
e-mail in May. "If we had not considered the influencing factors well
enough, thermal and stress adjustments would tell us."

If the railway has done well this far, as he says it has, then it will
likely withstand whatever stresses the climate throws at it next?at
least for awhile.

Abrahm Lustgarten is a reporter at ProPublica and is the author of
China's Great Train, Beijing's Drive West and the Campaign to Remake
Tibet, which was released in paperback in May.
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