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Determining the Local Implications of Global Warming

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Determining the Local Implications of Global Warming Professor Clifford Mass, Eric Salathe, Patrick Zahn, Richard Steed University of Washington – PowerPoint PPT presentation

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Title: Determining the Local Implications of Global Warming


1
Determining the Local Implications of Global
Warming
Professor Clifford Mass, Eric Salathe, Patrick
Zahn, Richard Steed University of Washington
2
Project Support
  • King County
  • Seattle City Light
  • EPA STAR Program
  • NOAA
  • Climate Impacts Group

3
Questions
  • What are the implications of global warming for
    the Northwest?
  • How will our mountains and land-water contrasts
    alter the story?
  • Are there some potential surprises?

4
Regional Climate Prediction
  • To understand the impact of global warming, one
    starts with global circulation models (GCMs) that
    provide a view of the large-scale flow of the
    atmosphere.
  • GCMs are essentially the same as global weather
    prediction models but are run with much coarser
    resolution and allow the composition of the
    atmosphere to vary in time (e.g., more CO2)
  • Even leading GCMs only describe features roughly
    500 km or larger in scale.

5
  • Northwest weather is dominated by terrain and
    land-water contrasts of much smaller scale.
  • In order to understand the implications of global
    changes on our weather, downscaling of the GCM
    predictions considering our local terrain and
    land use is required.

6
Annual Precipitation
7
Downscaling
8
Downscaling
  • The traditional approach to use GCM output is
    through statistical downscaling, which finds the
    statistical relationship between large-scale
    atmospheric structures and local weather.
  • Statistical downscaling either assumes current
    relationships will hold or makes simplifying
    assumptions on how local weather works.

9
Downscaling
  • Such statistical approaches may be a reasonable
    start, but may give deceptive or wrong answers
    since the relationships between the large scale
    atmospheric flow and local weather might change
    in the future.

10
Downscaling
  • There is only one way to do this right running
    full weather forecasting models at high
    resolution over extended periods, with the large
    scale conditions being provided by the GCMs.this
    is called dynamical downscaling.
  • Such weather prediction models have very complete
    physics and high resolution, so they are capable
    of handling any surprises

11
Example of Potential Surprises
  • Might western Washington be colder during the
    summer under global warming?
  • Reason interior heats up, pressure falls,
    marine air pushes in from the ocean
  • Might the summers be wetter?
  • Why? More thunderstorms due to greater surface
    heating.

12
Downscaling
  • Computer power and modeling approaches are now
    powerful enough to make dynamical downscaling
    realistic.
  • Takes advantage of the decade-long work at the UW
    to optimize weather prediction for our region.

13
UW Regional Climate Simulations
  • Makes use of the same weather prediction model
    that we have optimized for local weather
    prediction the MM5.
  • 10-year MM5 model runs nested in the German GCM
    (ECHAM).
  • MM5 nests at 135km, 45km, and 15 km model grid
    spacing.

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MM5 Model Nesting
  • 135, 45, 15 km MM5 domains
  • Need 15 km grid spacing to model local weather
    features.

16
Regional Modeling
  • Ran this configuration over several ten-year
    periods
  • 1990-2000-to see how well the system is working
  • 2020-2030, 2045-2055, 2090-2100

17
Details on Current Study GCM
  • European ECHAM model with resolution roughly
    equivalent to having grid points spaced 210 km
    apart. Can resolve features of roughly 850 km
    size or more.
  • IPCC climate change scenario A2 -- aggressive CO2
    increase (doubling by 2050)


IPCC Report, 2001
IPCC Report, 2001
18
ECHAM Global Climate System Model
19
Global Forcing Surface Temperature
20
First things first
  • But to make this project a reality we needed to
    conquer some significant technical hurtles.
  • Example diagnosing and predicting future deep
    soil temperatures
  • Example requirements for acquiring GCM output
    every 6 h and storing massive amounts of output.
  • Evaluating the 1990-2000 simulations

21
Evaluating of Model Fidelity
  • We have carefully evaluated how well the GCM and
    the MM5 duplicated the 1990-2000 period.
  • We previously had run the system using another
    GCMthe Parallel Climate Modelwith
    unsatisfactory results.crazy cold waves during
    the winter.
  • ECHAM Model appears far betterbut not perfect.

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Too Cold
  • Cold episodes occurred 1-2 times per winter with
    temperature getting unrealistically cold (below
    10F) in Puget Sound
  • Also a general cold bias to minima
  • Better than previous attempts.

24
Why Cold Outbreaks?
  • Widespread surges of arctic air originate in
    ECHAM5, likely owing to poorly-resolved terrain
    (Cascades and Rockies).
  • Extreme cold air inherited by MM5.
  • Results from previous experiments with
    lower-resolution (T42) GCM indicate that higher
    resolution reduces frequency and severity of
    unrealistic cold events.

25
Evaluation of Future Runs
  • Because there are some biases in the GCM runs,
    results for future decades (2020s, 2040s, and
    2090s) will be evaluated against the ECHAM5-MM5
    1990-2000 baseline

26
Now, The Future
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36
Why Such Strong Warming on Mountain
Slopes..Particularly in Spring?
  • Probable Answer Snow melt resulting in more
    solar heating.

37
Change in Water Of Snowpack ()
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40
Snow and Ice Reflect Much of The Incoming Solar
Radiation
Solar Radiation
Now
41
Global Warming Causes Snow level to Rise
Resulting In Absorption of Solar Energy on Melted
Slopes
Solar Radiation
Future
WARMING
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43
Why Cooling West of Cascades in Spring?
  • Low clouds due to more onshore flow from off the
    cool, cloud Pacific.
  • The Montereyization of the western lowlands!

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51
Precipitation
  • Bottom Line No Large Regional Trends

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Summary
  • The viability of the approachusing high
    resolution numerical prediction models forced by
    large-scale general circulation climate models
    (GCMs) has been demonstrated.
  • Careful evaluation of the GCM output is
    requiredthere are deficiencies.
  • Although there is general warming over the region
    for all seasons, the terrain and land water
    contrasts of the region enhance or weaken the
    warming in certain areas.

59
Summary
  • Warming is enhanced on the upper windward slopes
    due to snow melt.
  • Springtime warming is lessened west of the
    Cascade crest due to more low clouds.
  • Many more hot days during the summer.
  • Precipitation changes are more modest then
    temperature changes.
  • There will be a substantial loss of snowpack,
    reaching catastrophic decreases by 2090.

60
Future Work
  • We are just in the beginning of this work.
  • Need to find and remove causes of biases and cold
    outbreaks
  • Need to test other global warming scenarios
  • Will try to find higher resolution GCMs
  • Try more sophisticated MM5 physics
  • More analysis.

61
The END
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