Determining the Local
Implications of Global Warming
Clifford Mass
University of Washington
Global Warming 101
The Earth With No Atmosphere
(infrared)
Earth’s surface would be 60F cooler than today…no life.
But the Earth has an
atmosphere!
• Includes gases
such as nitrogen
and oxygen
• Also includes
greenhouse
gases.
What is a Greenhouse Gas?
• Greenhouse gas is a gas that that is
relatively transparent to solar radiation, but
absorbs and emits in the infrared…the type
of radiation the earth emits.
• Some examples:
– Water vapor
– Carbon dioxide
– Nitrous oxide
– Methane
Earth With An Atmosphere That
Includes Greenhouse Gases
Partly
(infrared)
Greenhouse Gases Make the Earth Warmer by Slowing the Loss of Infrared Radiation
Greenhouse Gases Warm the
Earth in a Similar Way That
Blankets Warm Us at Night
The Problem:
Rapidly Rising Greenhouse
Gases Due to Mankind
Gases Trapped in Ice Gives Us a History of the
Gases in the Atmosphere
But it is worse than that…
• There are a number of natural “amplifiers”
of mankind’s emission of greenhouse
gases.
• The warming due to increased carbon
dioxide, methane, and other greenhouse
gases will cause more water to be
evaporated from the earth’s oceans.
Amplifier
• The amount of evaporation increases with
temperature.
• Water vapor is the most potent greenhouse
gas and thus causes even MORE warming.
• This produces a positive feedback.
But it gets
even worse…
• Warming temperatures melt snow and ice.
• Snow and ice help cool the planet because they
reflect much of the sun’s radiation….that is why
you need sun glasses while skiing.
• As the snow melts less radiation is reflected to
space and more is absorbed.
• Thus, the earth gets warmer, which melts more
snow.
• Another positive feedback!
Is Global Warming Already
Happening?
• Finding the global warming signal is made more
difficult because the earth’s climate has a certain
amount of natural variability.
• Also the warming due to man was relatively
small before the middle of last century before the
large increase in fossil fuel usage.
• The consensus of most atmospheric scientists is
that some global warming signal due to man is
now evident.
Eleven of the twelve warmest years
in the past 150 years have
occurred in the past twelve years
(1995-2006)
But Not All “Signs” of Global
Warming Are Due to Mankind
These photographs, taken in 1928 and 2000, show
how South Cascade Glacier in the Washington
Cascade Mountains has retreated over time.
BUT…this melting began prior to the period when
mankind could have had much of an impact.
Represents the end of the Little Ice Age.
But what about the future?
The Technology of Prediction
• Atmospheric scientists use complex climate
prediction models…called General Circulation
Models…GCMS…to predict the future climate.
• These models are similar to weather forecast
models, but allow the gases in the atmosphere
to change.
• They also simulate the evolution of the oceans.
• Have to assume the future emission of
greenhouse gases by mankind…call
scenarios..a major uncertainty.
• These models are not perfect and cannot exactly
replicate the current climate….but they are close
and getting better each year.
Details on Current Study: GCM
• Which Scenario Will Mankind Follow?
IPCC Report, 2001
IPCC Report, 2001
IPCC.AR4.2007
Sample Climate Model Output for 2100
What about the Northwest?
• Several of us are applying very high
resolution simulations forced by the global
climate model predictions
• Gives a view of the local implications of
global warming.
• Could our mountains and other local
features make it worse or better?
•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, we must
consider our local
terrain and land use.
Running High Resolution
Climate Models
135, 45, 15Regional
km MM5 domains
•
• Need 15 km grid spacing to model local weather features.
Snow and Ice Reflect Much of
The Incoming Solar Radiation
Solar Radiation
Now
Global Warming Causes Snow level to Rise
Resulting In Absorption of Solar Energy on
Melted Slopes
Solar Radiation
Future
=WARMING
Why Relative 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!
Large Drop in Snowpack in the Mountains
Key Facts
• The overwhelming majority of atmospheric
scientists believe global warming forced by
mankind’s changes to the atmosphere has
occurred and will became MUCH larger during
the next decade.
• This is based on the best technology and
observations available.
• There are substantial uncertainties, so we can’t
give a specific number, but a range.
• Even if increases in the emission of greenhouse
gases stop today, a certain amount of global
warming is inevitable.
Range of Global Warming
Global Warming Goes Political
and Reaches the Public Arena
Inconvenient
Truth: Basically
Accurate But
Contains Some
Errors
Downplays
Global
Warming:
Full of Major
Errors
Mayor Nickels and Global
Warming
• Claims of a 50% reduction in Cascade
snowpack due to global warming are
simply not true.
• Perhaps 10-15%
Little Change In Snowpack Over
the Last 30 Years
• More flooding
and heavy rains
under global
warming?
• Not necessarily
if the jet stream
moves
northward.
Bottom Line
• Global warming and its local implications
are very serious.
• There are significant uncertainties, but
they are NOT in whether global warming
will occur, but rather the magnitude and its
local effects.
The End