Future Climate Change in the
Pacific Northwest
Cliff Mass, Atmospheric Sciences
University of Washington
March 11, 2015
Global warming is one of the
central issues of this century
But what
will
happen
here?
We need answers asap
• Global warming is going to happen: mankind
is doing very little to stop it.
• We are putting in infrastructure now (e.g.,
drainage systems, roads) that will be in place
50-100 years.
• Are new or altered reservoirs/dams needed?
• For land use planning and potentially moving
people/businesses to safety.
There has been a great deal of
contradictory information about
global warming and its influence
on the Northwest
Some environment
groups have
proposed that
global warming has
already caused our
precipitation to
become more
extreme
Seattle’s mayor and others suggested
our snowpack had declined by 50%
Local media have aired stories saying
storms are getting more intense
In contrast, others hold that
there is no strong evidence for
current or future changes …or
that the earth is cooling
ill
Some suggest that increasing CO2
is acidifying our local waters killing
billions of oysters
While others suggest very little
impact on oysters or other shellfish
Some suggest that the recent “pause”
means global warming is not occurring
…while thousands of scientists
from around the world have
written a series of reports
indicating the imminent threat of
global warming due to mankind’s
influence
Intergovernmental Panel on
Climate Change (IPCC) Reports
The global warming debate has
degraded into tribal warfare
“Alarmist”
“Luke Warmer”
“Denier”
That is certainly true in WA State
What can climate prediction
technology tell us? What do we
know for sure? What are the
uncertainties? What will happen
here?
That is the topic of this talk
Human-forced (anthropogenic)
climate change has already hit our
region
Even without any effects from
increasing greenhouse gases
Massive Irrigation in Eastern WA
The result: cooling of 1-4 °F
and higher humidity
Plowed fields: Eastern WA dust
storms
Urban heat islands have developed in
our major cities (more concrete, drier
surfaces, etc.)
Seattle’s urban core is often 2-10F
warmer than it would have been
without concrete and buildings
Regional dams have radically changed
flows in NW Rivers
Spring flooding on the Columbia no
longer occurs
Vanport, Oregon
June 1948
Particles from combustion have
changed our clouds
Ship tracks
caused by
particles
emitted by
commercial
shipping
Contrails reduce solar radiation
There are many more examples of
human impacts on weather, climate,
and water resources
Bottom Line
• Humans have already changed the climate
over our region
• Most of these changes have been largest near
the surface.
Natural Variability
• Even if there were no humans around,
weather and climate in our region would
vary in time.
• To understand the importance of
anthropogenic global warming, one must
start with a knowledge of natural variations.
Why is there natural variability?
• Complex interactions
between the atmosphere
and oceans.
• Volcanic eruptions
• Non-linear complex
processes in the
atmosphere or ocean.
• Variability in solar
radiation.
El Nino
El Nino and La Nina
El Nino
La Nina
The Pacific Decadal Oscillation (PDO)
Temperature
40 – 60 year cycle
Warm
Cold
Warm
Cold
Seattle Snow
Warm PDO
Phase
Cold PDO
Phase
48
70
95
The Northwest and much of the U.S.
warmed in the late 19th century and
first half of the 20th century
Most of the change resulted from
natural variability
NOAA observations over the NW
Mainly Natural
Natural & Anthropogenic
Northwest glaciers: started
melting before human’s had a
significant effect
South Cascade Glacier
Nisqually Glacier
1997
1976
1956
1941
1910
1825
Climate Change in the Northwest
• Past climate change in the NW was mainly the
result of natural variability
• Human impacts have been substantial where
we greatly modified the surface.
• But there is now a new player, one that will
increase in time and influence the full
atmosphere.
Increasing
Greenhouse
Gases
Greenhouse gases warm the
planet
•
•
•
•
•
Carbon Dioxide
Water Vapor
Methane
Nitrous Oxide
… and others
Greenhouse Gas
Emissions
The basic physics has been known for
a long time
Svante Arrhenius, 1896
We understand the greenhouse
effect
Graphic courtesy of the National Park Service
Greenhouse gases act like a blanket
Thicker blankets (or more of them)
make you warmer
Concentrations are increasing
rapidly
We can predict the impacts of
increasing greenhouse gases using
global climate models
• Sophisticated computer simulations based on the
physics of the atmosphere and ocean.
• Atmospheric parts are nearly identical to weather
prediction models, which are tested every day, but
with atmospheric gases vary in time.
Can we predict climate decades
ahead when we can’t forecast
next week’s weather?
In weather prediction we forecast
the exact state of the atmosphere
at some time in the future
• Tomorrow’s high in Spokane will be 67F
• It will rain tomorrow afternoon after 3 PM
In Climate Prediction We DON’T
Do This
• We predict average quantities over extended
periods.
• Example: the mean winter temperatures will
be 3F higher over the Pacific Northwest.
• The average conditions are closely controlled
by the amount of radiation reaching and
leaving the planet
• We have a good handle in changes in
radiation, IF WE KNOW THE ATMOSPHERIC
COMPOSITION.
Climate Prediction Technology
• We run coupled global atmosphere-ocean
models for decades or centuries.
• Use the most powerful supercomputers.
• Have to make assumptions about greenhouse
gas emissions. How will they change in time?
• There about two-dozen international groups
doing such simulations.
Climate Model Output for 2100
Global Warming is NOT Uniform
• Arctic warms quickly for a number of reasons,
including the melting of sea ice.
• Continents warm up more than oceans.
• Eastern oceans up less than western oceans.
• In general, the dry areas (e.g., the SW U.S.) get
drier and wet areas (e.g., British Columbia) get
wetter.
But there are issues with global
climate models …
They don’t necessarily agree
Surface Temperature Change from
1970-2000 compared to 2070-2100
Some climate models can’t simulate
the current climate well: some appear
too sensitive to greenhouse gases
Global climate models are too
coarse to simulate the effects of
critical Northwest terrain
Climate Model Terrain
A new technology to solve the
resolution issue:
Regional Climate Modeling
Regional climate modeling: Run
high-resolution simulations for
decades or a century for a limited
domain. Surface air temperature change
Global versus regional climate
models
Regional climate model
Global model
Regional Climate Modeling
• A handful of such simulations have been
completed. Demands large computational
resources
• Needs to be done many times using different
global climate model outputs.
• Needs sophisticated statistical processing of
the output to provide reliable information
• UW is now trying to find the resources to
build such an effort.
Uncertainty: Get Used to It
• Considerable uncertainty regarding
global temperature changes (roughly
1.5 to 4 C for doubling CO2)
• Even more uncertainty for local
changes
• Uncertainty in emissions of greenhouse
gases
What can we say about the future
climate of our region?
• There are some common features in many of
the future simulations.
• The trends of the past decades provide further
hints.
• What do they tell us?
Temperature
Northwest warming delayed and
slowed by the Pacific Ocean
Observed Winter Surface Temperature Change (1975-2014)
Consistently, NW Snowpack has NOT
declined during the past 30 years
Initial forecasts from a highresolution regional climate
simulation
• Assuming mankind continues business as
usual in burning carbon-based fuels.
Change in Winter Surface Air Temperatures (F)
What about water, our most
precious resource?
Good news for average
precipitation
Unlike some areas, we will still
have plenty of precipitation, just
more rain and less snow
Wetter
Winter
CMIP5 17-member
multimodel, multirun ensemblemean precipitation
change (mm
day−1) for RCP8.5
for 2070–99
relative to 1961–90
base period for
(top) DJF and
(bottom) JJA
Slightly
Drier
Summer
NCAR Global Model (Winter
Precipitation Trend, 2005-2060)
But warming will result in more precipitation
falling as rain rather than snow
Change in
Snowpack
from 1990
to 2090
-40%
0%
+40%
Welcome to the future. This year
is a lot like 2050-2070
• Warm, near normal precipitation, very low
snowpack
But there is a dark side to the our
future warmth: more extreme
precipitation and flooding
Super Atmospheric Rivers
A.K.A.: Pineapple Express
When atmospheric rivers hit our
terrain, intense precipitation falls
Global warming will intensify
atmospheric rivers
• Warmer air holds more water vapor.
• Examined a large collection of climate models
simulation for changes from 1970-2000 to
2070-2100 based on “business as usual”
greenhouse gas emissions.
• Winter-mean precipitation along the West
Coast increases by 11-18% while precipitation
on extreme atmospheric river days increases
by 15-39% .
Flooding Potential Increases
• Snow absorbs and helps to buffer heavy rain
events.
• With less snow, there will be less “protection.”
• Thus, heavier rainfall could lead to greater
flooding on major rivers.
Northwest Windstorms
• Will there be more of them?
• Will they become more intense?
The Inauguration Day Storm
1993
Northwest Windstorms
• The answer appears to be no. No increasing
trend.
• UW investigated this issue for Seattle City
Light
Number of times per year winds
exceed a high-wind threshold (DJF)
at Seattle for several simulations
The source of energy of NW storms,
the jet stream, hardly changes
• Horizontal temperature gradients drive the jet
stream
• Most global climate models suggest that the
temperature gradients will weaken at low
levels as the Arctic heats up more than the
poles.
• But the temperature gradient increases in
upper troposphere as the tropics warm aloft.
• Together, there is little change in the jet
stream.
Winter (N-F) east-west wind at
18,000 ft: climate model average
(1970-1999)
Meters
per
sec
Future (2070-2099)
Tropical cyclones (hurricanes)
hitting the Northwest?
Forget it, even a warmed eastern Pacific will be
far too cold (need 80F water!).
We are better off than most folks
Why are we fortunate?
• We will still have as much, if not more, water.
• The Columbia River drains off high terrain, so
flow should be maintained for many years.
• We will warm, but the increases will be
lessened and slowed by the Pacific Ocean.
• There is no reason to expect stronger
windstorms or thunderstorms.
• Flooding will increase, but that will be mainly
limited to areas adjacent to rivers.
Major Take Home Messages
• Global warming from greenhouse gases has had
only a small influence on our region so far.
Natural variability has dominated over human
forcing.
• That will change, particularly by the end of the
century. Less warming near the coast, more in
eastern Washington. Think 3-8F during the
winter.
• Annual precipitation will remain the same or
increase slightly
Take Home
• Significant (30-70%) drops in mountain
snowpack by the end of the century
• Atmospheric rivers will be stronger, with
heavier rainfall and more flooding.
• No increase in windstorms
• Beware those that hype current weather
events as indications of global warming.
• Those who claim that GW is not an issue are
equally wrong.
The End