The Seattle Times
Wednesday, August 6, 2008 – Page updated at 12:00 AM
UW study examines decline of snowpack
By Warren Cornwall
Seattle Times environment reporter
Maybe the snow in the Cascade Mountains isn’t in
such immediate peril from global warming after
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 Mountain snowpacks.
Past studies have frequently focused on steep
declines in Cascade snowpack in the second half
of the 20th century, with drops measuring 30
percent 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
percent. 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
“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
Mass and his colleagues also predict the oceans
could help buffer Washington’s snows from
immediate impacts of climate change. A number of
computer models show the northeast Pacific
warming more slowly than most of the world’s
oceans, Mass said.
That could help keep temperatures in higher
altitudes, which would mean the difference
between rain and snow in the Cascades, from
rising quickly over the next few decades, Mass
But, Mass doesn’t say there’s nothing to worry
about. The Northwest is still on course for a big
drop in snowpack – and the accompanying
water-supply problems – by the end of the 21st
“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
Center. 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 in 2008. 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 was on vacation this week and couldn’t be
reached to review the latest study.
But Hamlet disagrees with Mass that the snowpack
drop could be explained mostly by fluctuating
ocean conditions. The Cascade snowpack trends in
the second half of the century are consistent
with rising temperatures in the western United
States, which have been tied to global warming,
Hamlet also criticizes some of the statistical
analysis in the new study, saying it could
exaggerate the role of decade-to-decade changes
in ocean conditions while understating other
potential influences, including global warming.
“I just don’t think the science is there,” Hamlet said.
Ocean conditions are hard to predict, Hamlet
argues, making it impossible to predict snowpack
levels over the next few decades. But in the long
term it’s safe to bet that rising temperatures
are going to mean less snowpack.