Measuring the meltdown By Jane Qiu [NATURE NEWS, 10 November 2010]

More than a billion people rely on drinking water fed by Himalayan glaciers such as Khumbu in Nepal. This supply could be at risk unless glacial retreat is stopped. J. BENDIKSEN/MAGNUM PHOTOS

Cold,
remote and threatened by global warming: the description applies not
only to the North and South Poles, but also to a region of more than
five million square kilometres, centred on the Tibetan plateau and the
Himalayas, that researchers call the third pole (see Nature 454, 393–396, 2008).
After the Arctic and the Antarctic, the region has Earth’s largest
store of ice, in more than 46,000 glaciers and vast expanses of
permafrost. Yet it is much less studied than its high-latitude
counterparts, even though many more lives depend on it. The
third pole is also known as Asia’s water tower, because its glaciers
feed the continent’s largest rivers, which sustain 1.5 billion people
across ten countries. Those glaciers are melting fast, filling lakes
that can overflow and flood valleys. Yet little is known about how
climate change is unfolding there. To attempt to rectify this, Third
Pole Environment (TPE), an international programme led by the Chinese
Academy of Sciences’ Institute of Tibetan Plateau Research (ITP) in
Beijing, held its second workshop last month in Kathmandu. Researchers
in the region laid plans to fill the knowledge gap, and discussed
findings that add to the urgency. “Everyone is doing important
work across the region, but it is unclear how they fit together,” says
Yao Tandong, director of the ITP and chairman of the TPE science
committee, which helped to organize the workshop. “The only way forward
is for the international community to work together to assess the risks
associated with climate change,” he says. As the region’s
population booms, the top priority of researchers is to understand the
status and fate of glaciers that are a vital source of drinking water.
Last year, a claim in the 2007 report of the Intergovernmental Panel on
Climate Change (IPCC) that Himalayan glaciers could disappear by 2035
turned out to be an error (see Nature 463, 276-277; 2010). But
participants at the workshop argued that the IPCC’s broader concern
about the rapid loss of Himalayan glacier ice was correct. “There is no
doubt that many of the glaciers in the region are retreating fast,”
says Baldev Raj Arora, former director of the Wadia Institute of
Himalayan Geology in Dehradun, India. But it is not clear
exactly how fast, or how this will affect water resources, because
there is no glacier inventory for the entire region. Taken alone,
satellite studies offer only a rough estimate of glaciated area, and
remoteness, high altitudes and harsh weather conditions hamper
measurement from the ground. The evidence that is available is
telling. Using a combination of satellite and ground measurements, a
team led by Liu Shiyin, a glaciologist at the Chinese Academy of
Sciences’ Cold and Arid Regions Environmental and Engineering Research
Institute in Lanzhou, has just completed the second Chinese national
glacier inventory, documenting some 24,300 glaciers and recording
characteristics such as their locations, lengths and surface areas. It
shows that the total surface area of glaciers has decreased by 17% and
that many have disappeared since the last inventory began, roughly 30
years ago. To get a better estimate of such changes,
researchers have also measured the ice volume and mass balance of
representative glaciers in various parts of the Himalayas. Such arduous
studies, often at altitudes above 5,000 metres, show that “the impact
of climate change on some Himalayan glaciers is much worse than
previously thought”, says Tian Lide, a glaciologist at the ITP. The
expansive Kangwure glacier on the northern slope of Mount Xixiabangma
in southern Tibet, for instance, has lost nearly half of its ice since
the 1970s, and its average thickness has decreased by 7.5 metres. Most
of the glaciers in the Indian Himalayas that have been studied in
detail are also losing mass, says Arora. Across the third pole,
“regional anomalies exist, but the balance of evidence certainly points
towards a trend of fast retreat”, agrees Lonnie Thompson, a
glaciologist at Ohio State University in Columbus and a co-chairman of
the TPE science committee. Carbon toll One
cause of the retreat is the growing amount of sooty ‘black carbon’ made
by fossil-fuel and biomass burning. Xu Baiqing, an environment
scientist at the ITP, measured 50 years’ worth of black-carbon levels
in ice cores from five glaciers in various parts of the Himalayas, and
found increased emissions since the 1990s, coinciding with rapid
industrial growth in the region. Angela Marinoni, a climate scientist
at the Institute of Atmospheric Sciences and Climate in Bologna, Italy,
and her colleagues found high concentrations of aerosols, including
black carbon, above 5,000 metres in the Nepalese Himalayas, which
caused significant atmospheric warming. They calculate that deposition
of black carbon could increase snow and ice melting of a typical
Himalayan glacier by 12–34%, by reducing its ability to reflect light. As
a consequence, glacial lakes are getting larger and more numerous,
causing more floods. A study led by Yongwei Sheng, an ecologist at the
University of California, Los Angeles, shows that the area of such
lakes on the plateau has increased by 26% since the 1970s, with a
devastating effect on surrounding pastures. Outbursts of glacial lakes
have caused more than 40 floods in the Himalayas since the 1950s, and
more are likely in the coming decades, says Pradeep Mool, a
remote-sensing specialist at the International Centre for Integrated
Mountain Development (ICIMOD) in Kathmandu. An ICIMOD survey listed
more than 20,200 glacial lakes in the region; two hundred are
“potentially dangerous” and need close monitoring and an early warning
system, says Mool. So far, scientists trying to forecast the
glaciers’ future have had little to go on. For one thing, says
Thompson, “glaciers respond to climate differently depending on their
size, altitude distribution, surface area, debris cover and valley
characteristics”. And little is known about how climate is changing
across the third pole. Yang Kun, a climate scientist at the
ITP, found that many satellite-based measurements of Earth’s radiation
budget — the balance of incoming solar radiation and outgoing heat —
did not work well at the third pole’s high elevations, because
instruments are typically calibrated and verified against ground-truth
data from the lowlands. They can be corrected using field measurements,
but across the region, only 16 weather stations lie above 5,000 metres.
Investigators can’t rely on climate models, either. Using data
from the only weather station at 8,000 metres, on the South Col pass
between mounts Everest and Lhotse, Kenichi Ueno, a climate scientist at
the University of Tsukuba, Japan, showed that global climate models do
not predict moisture and radiation flux well at such high altitude,
especially in hot weather or monsoon season. “If you want to know how
climate affects glaciers, such details are crucial,” he says. “It’s
extremely important to have more high-altitude observations across the
region.” A joint endeavour The TPE science
committee will soon draft a research programme to document the effects
of climate change on glaciers, permafrost, water resources,
biodiversity and people. The plan, to be finalized by autumn 2011, will
call for joint expeditions to the Himalayas and the Tibetan plateau,
and for multidisciplinary research stations across the region, to cover
key geological areas and climate regimes as well as important river and
lake basins. Once costs have been defined, the committee will seek
support from national and international funding agencies. The
most important part of the plan is a common data repository, says
Volker Mosbrugger, director of Senckenberg World of Biodiversity, a
coalition of research institutes and museums in Frankfurt, Germany, and
another co-chairman of the TPE science committee. But national
rivalries may stand in the way, especially when the shared data concern
water resources. “Whether there can be a central database up and
running will determine whether the programme can move beyond its
rhetoric,” says Gregory Greenwood, director of the Mountain Research
Initiative at the University of Bern. “This will be a great challenge.”
The committee will draft a policy to be negotiated between
countries interested in the programme, letting scientists share
information but leave out data deemed politically sensitive. “Without
working together and pooling data from across the third pole,” says
Yao, “comprehensive understanding of climate impact and feedback
mechanisms would be impossible.”