Global Warming 101
Huge Amount in the Media on this
Issue
Inconvenient
Truth: Basically
Accurate But
Contains Some
Errors
Downplays
Global
Warming
The Day After Tomorrow: Global
Warming Causes Ice Age:
Complete Nonsense
“Greenhouse Warming” Makes
Earth Liveable
The Earth With No Atmosphere
(infrared)
Earth’s surface would be 60F cooler than today…no life.
But the Earth has an
atmosphere!
• Dominated by
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 absorbers and emits in
the infrared…the type of radiation the earth and clouds
emits.
• Some examples:
– Water vapor
– Carbon dioxide
– Nitrous oxide
– Methane
– Chlorofluoromethanes
Earth With An Atmosphere That
Includes Greenhouse Gases
Partly
(infrared)
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.
Why?
• The amount of evaporation increases with
temperature.
• Water vapor is the most potent greenhouse
gas and thus causes even MORE warming.
• This is caused 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!
The Technology of Climate
Prediction
• Atmospheric scientists use complex climate
prediction models…called General Circulation
Models…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…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
How good are are climate models?
• The technology is constantly being tested
and improved in our weather prediction
models.
• But even more important, how well can we
duplicate the climate of the past hundred
years?
IPCC.AR4.2007
Range of Global Warming
Sample Climate Model Output for 2100
Projections of Future Changes in Climate
Projected warming
in 21st century
expected to be
greatest over land
and at most high
northern latitudes
Subtropics Dry, Midlatitudes/Polar
Regions/Tropics Moisten
WInter
Summer
What about the Northwest
• Several groups are using 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?
Large Drop in Snowpack in the Mountains
The END
Bottom Line
• Global warming and its local implications are
serious.
• There are significant uncertainties, but they are
NOT in whether global warming will occur, but
rather the magnitude and its local effects.
But even without human-caused
greenhouse warming the earth’s
climate would change
Eccentricity
Obliquity and Precession
Periodic Ice Age
Axis in
approximately
11,000 years
Axis now
January
(b) Conditions now
23 1/2°
July
(a)
July
January
(c) Conditions in about 11,000 years
Editable Text
Fig. 14-11, p. 395
Fig. 14-12, p. 396