Global Warming: The Basics and
Implications for the Northwest
Cliff Mass, University of Washington
There is a great deal of
contradictory information about
global warming
A variety of local environment groups have
proposed that global warming has caused our
weather to become more extreme
In contrast, others
hold that the lack
of warming of the
planet during the
past ten years
indicates that
global warming is
no real threat
George Will
..and that scientific consensus is a
myth
Some ask:
How can scientists predict climate when they
can’t get the next week’s weather forecast right?
…but 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
IPCC Reports
What is the truth? What is biased
and wrong? What do we know for
sure? What are the uncertainties?
What will happen here?
The Problem:
greenhouse
gases are
increasing
Greenhouse Gases Act as
Atmospheric “Blankets” and Warm
the Earth
•
•
•
•
•
Carbon Dioxide
Water Vapor
Methane
Nitrous Oxide
… and others
We understand the greenhouse
effect
Graphic courtesy of the National Park Service
We Can Predict the Future Effects of More
Greenhouse Gases Using “Climate Models”
• Sophisticated computer simulations based on
the physics of the atmosphere.
• Nearly identical to weather prediction models,
which are tested every day.
• These models are very good, but not perfect.
A Major Question Is How Greenhouse Gas
Emissions Will Change in Time
Substantial Uncertainties of the Magnitude of the Forcing Exist
Warming Is Clear But Substantial
Uncertainties Exist
Climate Model Output for 2100: Global Warming
Will Not Be Uniform
Global Models Do Not Have the Resolution to
Describe the Local Implications of Global
Warming—Regional Downscaling is Needed
Bottom Line
• It is clear that the earth as a whole will warm
and that the rate of warming will increase
later in the century.
• There is substantial uncertainty in the
magnitude of the global warming during this
century (roughly 1-4°C globally).
• Even more uncertainty exists regarding the
local implications of global climate change,
both natural and man-induced.
Global Warming Implications in the
Northwest
• It appears that there has been very little
warming here during the past 30 years.
• This makes a lot of sense--our weather is
controlled by the Pacific and the eastern
Pacific is one of the last places that will warm
significantly.
• Although global warming will be weaker and
delayed here…it will happen in force by the
end of the century.
Cascade snowpack hasn’t changed in the
last 30 years
Change in Winter Surface Air Temperature (°C)
for 1979-2008
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
+0.2
+0.4
Air Temperature Trend (1979-2005)
+0.6
+0.8
+1.0
+1.2
+1.4
Can We Predict Climate 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.
• MUCH easier to do.
• Furthermore, the average conditions are
closely controlled by the amount of radiation
reaching and leaving the planet--and we can
figure that out fairly well.
Should we expect stronger storms
and more floods under global
warming?
We don’t know. And there is no certainty
that stronger storms will occur here.
• The number of windstorms and floods have
increased during the past decade or so in
Washington, but DECREASED in Oregon.
• Storms follow the jet stream --a current of
strong winds in the upper atmosphere--and
most climate models predict the jet stream
will weaken and move northward.
• Thus, it is possible that storms here might
WEAKEN or move away from us under global
warming.
Finally, does the lack of warming
during the last ten years mean
anything?
No, one should expect such level
periods
• Atmospheric temperature trends are a
combination of man-caused global warming
and natural variations, which are quite
significant.
• The global warming signal will increase rapidly
this century, but natural variations will not.
• So one expects some short periods when
natural cooling balances out global warming.
• Eventually, man-induced global warming wins.
Regional Simulations of the Local
Impacts of Global Warming
Change in Winter Surface Air Temperatures (F)
Change in Snowpack from 1990 to 2090
-40%
0%
+40%
Advice: Don’t buy this after 2050!
Bottom Line
• The earth will warm substantially during this
century, but there are considerable
uncertainties.
• Global warming will be delayed here, but
substantial changes will occur by the end of
the century
The End
PDO