Download Human-forced climate change has already hit our region

Future Climate Change in the
Pacific Northwest
Cliff Mass, Atmospheric Sciences
University of Washington
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
And 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
ill
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
What can climate prediction
technology tell us? What do we
know for sure? What are the
uncertainties? What will happen
here?
Human-forced (anthropogenic)
climate change has already hit our
region
Even without any effects from
increasing greenhouse gases
like CO2
Massive Irrigation in Eastern WA
The result: cooling of 1-4 °F
and higher humidity
Plowed fields: Eastern WA dust
storms
Seattle’s urban core is often 2-10F
warmer than it would have been
without concrete and buildings
Bottom Line
Humans have already changed the climate
Increasing
Greenhouse
Gases
Greenhouse gases warm the
planet
•
•
•
•
•
Carbon Dioxide
Water Vapor
Methane
Nitrous Oxide
… and others
Greenhouse Gas
Emissions
Greenhouse gases act like a blanket
Thicker blankets (or more of them)
make you warmer
CO2 oncentrations are increasing
rapidly
We predict the impacts of increasing
greenhouse gases using global climate
models (GCMs)
• 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.
Climate Prediction Technology
• We run coupled global atmosphereocean 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.
Temperature
Northwest warming delayed and
slowed by the Pacific Ocean
Observed Winter Surface Temperature Change (1975-2014)
Without Pacific warming, our
mountain snowpack has not
changed much over 30 yr
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
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
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%
But there is a dark side to the our
future warmth: more extreme
precipitation and flooding
Super Atmospheric Rivers
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.
• Precipitation on extreme atmospheric river
days increases by 15-39% .
Flooding Potential Increases
• Snow absorbs rain.
• 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
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.
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