 Scientists report no clear evidence that human-induced climate change has caused a drop in 20th century snow levels
Maybe the snow in the Washington state's Cascade mountains isn't in such immediate peril from global warming after all.
Despite
previous studies suggesting a warmer climate is already taking a bite
out of Washington's snowpack, there's no clear evidence that
human-induced climate change has caused a drop in 20th century snow
levels, according to a new study by University of Washington scientists.
In
fact, the newest study also predicts the Cascade snows - vital to water
supplies, crop irrigation and salmon - could enjoy a delay in the
effects of global warming.
But the findings have already become
part of a scientific debate with an unusually political tone. It's an
ongoing disagreement that has UW researchers taking sides against each
other and has attracted the attention of political groups.
And a
leading scientist on the other side of the debate said the latest
analysis speculates about the future and offers little new about the
past.
"They're trying to forecast the next 20 years or so, and I
don't think they can do it," said Alan Hamlet, a UW hydrologist who has
written papers about historic Cascade snowpack.
Past studies have
frequently focused on steep declines in Cascade snowpack in the second
half of the 20th century, with drops measuring 30% or more.
But
Cliff Mass, a well-known UW meteorologist, said the new study, which he
co-authored, shows it all depends on which years are examined. He and
his co-authors argue snow levels were unusually high in the 1950s,
creating a distorted picture of historic patterns.
Measurement of
mountain snow levels were spotty before the 1950s, making it harder to
get a complete picture. But Mass and his colleagues tried to estimate
snowpack for earlier years based on measurement that did exist: the
amount of water that flowed down streams as snow melted.
Using
that method, they found a smaller drop in snowpack between the 1930s
and today – 23%. That still may sound like a big drop, but the
scientists argue that it could be statistically insignificant, so it's
hard to say whether it's meaningful. They also say that many of the
changes appear to be attributable to shifting weather patterns driven
by the Pacific ocean.
"We can't see the global-warming signature
in terms of a decline in snowpack," said Mark Stoelinga, the study's
lead author, and a professor in the UW's atmospheric sciences
department.
But, Mass doesn't say there's nothing to worry about.
The north-west US is still on course for a big drop in snowpack - and
the accompanying water-supply problems - by the end of the 21st century.
"We're
in a place that is not going to warm up as quickly," Mass said at a
recent conference by free-market think tank, the Washington Policy
Centre. But "eventually global warming will have a profound effect".
The study has not yet been peer-reviewed.
Hamlet
counters that the bigger historical picture - gradually declining
snowpack over the 20th century - has already been put forward, most
recently in a study published this year.
In fact, he wrote it,
along with state climatologist Philip Mote, another UW scientist who
has been a primary player in the ongoing dispute. Mote couldn't be
reached to review the latest study.
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