Global Warming and Its
Implications for the Pacific
Northwest
Cliff Mass
University of Washington
Presented at the WPC Climate Conference, July 15, 2008
Three Key Points
• Global warming forced by increased
greenhouse gases is inevitable and will
be highly significant in its effects on
mankind.
– The science is well understood and based
on fundamental physics and sophisticated
models.
– Uncertainties exists, but will not change the
essential results.
Three Key Points
• Outside of the Arctic, the global warming signal
during the past several decades has generally been
subtle and masked by the normal variability of the
climate system.
– In some cases, global warming “supporters’ have hyped
its current and past effects (e.g., Katrina, Cascade
snowpack reduction)
– In other cases, global warming “skeptics” have wrongly
dismissed global warming’s future influence based on
incorrect interpretations of the past and current climate
record (this spring’s cold spell) or brought up “red herring”
factors (solar variability).
Three Key Points
• Remember the global in global warming.
– Although the globe as a whole will warm, the
changes will NOT be uniform.
– Some areas (e.g., the polar regions) will
experience huge changes while in others the
effects will be far less.
– The Pacific Northwest may well be one of
those regions of delayed or lesser effects.
– The variability in local impact of GW is a key
research topic today… and an issue of great
societal importance.
Have Large Impacts of Global
Warming Already Occurred in
the Pacific Northwest?
Some claims:
• 30-50% loss of Cascade snowpack
• Maximum streamflow occurring 20-30
days earlier
• Heavier rain and more floods.
The truth is that there is no evidence that human
induced global warming has caused such
significant impacts. But that is not saying that they
won’t occur in the future.
Loss of Northwest Snowpack
Due to Global Warming
•Some local scientists and politicians
have claimed a loss up to 50% since
1950 and have either implied,
suggested, or explicitly stated that this
is due to global warming.
•Is this really true?
Scientific Consensus Statement Signed
by Several Dozen Prominent NW
Scientists for the Governor of Oregon
From Mote et al
2006
Washington-wide snowpack since 1950,
Relative to 1971-2000 normal
Snowpack in usual maximum month
Washington-wide snowpack period of record,
Relative to 1971-2000 normal
Snowpack in usual maximum month
New Research: Stoelinga, Mass, and Albright 2008
Proxy Oregon/Washington Snowpack (April 1 Snow Water Equ)
1 Apr SWE (percent of normal)
200
150
100
50
0
1930
1940
1950
1960
1970
1980
Water Year
1990
Trends Depend on When You Start
2000
2010
Cascade Snowpack has INCREASED during the past 30 years
1600
1976-2007 Trends in
1 Apr SWE for
Elevation Quartiles (EQs):
1400
EQ4: +7.1%
EQ3: +9.4%
EQ2: +7.8%
EQ1: +6.4%
1 Apr SWE (mm)
1200
EQ4
1000
EQ3
800
EQ2
600
EQ1
400
High
Low
200
0
1980
1985
1990
1995
Water Year
2000
2005
2010
Stoelinga et al 2008. Time series of elevation quartile (EQ)-averaged 1 April SWE (in mm) measured at
snow course during the period 1976-2007. Elevation ranges for the four quartiles are: (1) 792-1119 m; (2)
1119-1288 m; (3) 1288-1542 m; and (4) 1542-1981 m. Dashed lines show best-fit lines for each EQ. Also
listed are the 1976-2007 trends for each EQ (as percent of the 1961-1990 mean).
Pacific Decadal Oscillation
(PDO)
PDO is thought to be a natural mode of atmospheric variability
Negative phase of PDO associated with greater snowpack in NW.
Why has the Northwest
snowpack remained the same
or increased during the last
several decades while global
observations suggest we are
in the midst of a 30 year
warm-up period, one that
models suggest is due to
greenhouse gas emission?
IPCC
Report
Observations has shown that
the eastern Pacific has not
warmed up much during the
last thirty years.
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
+0.2 +0.4 +0.6 +0.8 +1.0 +1.2 +1.4
Air Temperature Trend (1979-2005)
Change in Surface Air Temperature (°C) from 1979-2008
General Circulation Model
Simulations for the Next
Century Also Suggest that the
Eastern Pacific Will Warm Up
Less Than Most of the Globe
Climate Model Output for 2100
Averaging a collection of the best GCMs over the Pacific
Suggests the Same Thing for the Future
(a) SST
SST
(b) Tsfc
0.0
+0.2
+0.4
(c) T850
+0.6
+0.8
Air Temp
+1.0
+2.0
+3.0
°C
850 mb
Stoelinga, Albright and Mass 2008
Predicted linear trend of November-March mean temperature
for 2000 to 2025 (°C), as predicted by the ensemble of climate
models used in the IPCC AR4 report. Shown are the ensemble
means of (a) sea-surface temperature, (b) surface air
temperature, and (c) 850-hPa temperature.
Delayed Warming in the
Pacific Northwest
• It appears that global warming’s effects will
be delayed in the Northwest due to its
proximity to the Pacific Ocean.
• But eventually, GW will have a profound
impact.
• The best technology to determining local
effects is downscaling general circulation
model simulations using high resolution
regional prediction models.
• Such work is ongoing at the University of
Washington
Large Drop in Snowpack in the Mountains Later in the Century
Precipitation
Bottom Line: No Real Trend in
Amounts or Extremes
The Precipitation Argument
You Often Hear
As temperature increases, so will
the amount of moisture in the
atmosphere, and thus there will be
more rain and heavy precipitation
events
Oct-Mar Precipitation (percent of normal)
October to March Precipitation Over the Cascades
From Stoelinga, Albright, Mass 2008
200
150
100
50
0
1930
1940
1950
1960
1970
1980
Water Year
1990
2000
2010
High
Resolution
Climate
Simulation
Why Simple
Arguments
Could Fail
• A number of theoretical, modeling, and
observational studies have suggested that
the jet stream will move northward under
global warming.
• Strong storms and heavy rainfall (pineapple
express situations) tend to follow the jet
stream.
• It is possible that the “action” could move
north of us under GW, with less major storms.
Is this already happening?
• Several studies have found a decline in
heavy precipitation over Oregon
• The number of major windstorms has
dropped over Oregon.
Summary
• The evidence that the world will warm up
profoundly due to greenhouse gas emissions is
compelling.
• The effects will not be uniform.
• The Northwest is located downstream of the Pacific
and thus will see lesser and delayed impacts.
• So far, the impacts over the NW have been
minimal.
• By the end of the century even the NW will
experience substantial warming and loss of
snowpack, unless actions are taken now to stabilize
and reduce greenhouse gas emissions.
Summary
• The climate system is complex, so
beware of simple arguments.