http://news.bbc.co.uk/2/hi/science/nature/925273.stm
Thursday, 14 September,
2000, 21:52 GMT 22:52 UK
Himalayan ice tells warming story
QUOTE:
"There is no question in my mind that the warming was,
in part, if not totally, driven by human activity"
Prof Lonnie Thompson
CAPTION:
"Xixabangma rises just over 8,000 metres"
Ice cores recovered from high in the Himalayas suggest the
1990s was the warmest decade for at least 1,000 years.
The cores were drilled
in a glacier flanking Xixabangma,
a 8,014-metre (26,293-foot) peak on the southern rim of
the Tibetan Plateau.
US and Chinese scientists
analysed the composition of the
different layers in the ice to build up a picture of the
regional climate year by year stretching back over the past
millennium.
The lead researcher,
Professor Lonnie Thompson, from Ohio
State University, said: "This is the highest climate record
ever retrieved, and it clearly shows a serious warming during
the late 20th Century."
The cores are also
said to show a clear record of at least
eight major droughts caused by a failure of the South Asian
Monsoon, the worst being a catastrophic seven-year-long dry
spell that cost the lives of more than 600,000 people at the
end of the 18th Century.
Volcanic activity
The international team,
which also included Peruvian, Russian
and Nepalese members, drilled a total of three cores in the
Dasuopu Glacier over a 10-week period.
The seasonal layers
in the ice were analysed for dust concentrations
and trace chemicals, and for the ratios of the different isotopes,
or types, of oxygen and hydrogen atoms.
The isotope ratios
were used to extrapolate the air temperatures
present when the ice was formed.
Dust concentrations
were used as an indication of dryness
or wetness in the region.
The presence of different
chemicals such as chlorides,
sulphates and nitrates were taken to be suggestive of
volcanic activity, fossil fuel burning and desertification.
Human activity
The researchers write
in the journal Science that their
analysis shows that both the last decade and the last
50 years were the warmest in 1,000 years.
They say the layers
covering the last century reveal
a four-fold increase in dust and a doubling of chloride
concentrations, suggesting an increase in dryness and
desertification.
Professor Thompson
said he was sure there was a clear
signature of human activity in the ice layers.
"There is no question
in my mind that the warming was,
in part, if not totally, driven by human activity,"
he said.
Proxy data
Some researchers still
doubt human activities are inducing
global warming.
They question not only
the accuracy of so-called proxy data
like ice cores but some of the conclusions drawn from them
- which they argue are based on debatable science.
They also point to
the inconsistencies in the various
temperature records.
Although surface data
gathered at weather stations show
a rapid warming over the last century, the atmospheric
data produced in the last few decades by satellite and
balloon studies show little or no warming.
The researchers believe
these inconsistencies must be
adequately explained before humans are blamed for climate
change.
For the last 25 years,
Professor Thompson and his colleagues
have drilled cores from glaciers and ice caps in some of the
most remote parts of the planet in an effort to recover records
of ancient climate.
Most current predictions
of global climate change suggest
that early signs of warming will be seen at high elevations
where these ice caps exist. So far, Professor Thompson's
work has borne this out.
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