The Greenhouse Effect
Global Warming 101
Huge Amount in the Media and the
Political Realm 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
In contrast,
others hold that
the lack of
warming of the
planet over the
past ten years
indicates that
global warming
is no real threat
George Will
..and that scientific consensus is
a myth
…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
Some ask:
How can scientists predict
climate when they can’t get the
next week’s weather forecast
right?
What is the truth? What is
biased and wrong? What do we
know for sure? What are the
uncertainties? What will happen
here?
“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
The Problem:
greenhouse
gases have
increased but
will continue to
increase
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.
• The amount of water vapor air can contains
increases rapidly 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.
• Use some of the largest supercomputers
in the world
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
Precipitation Subtropics Drier,
Midlatitudes/Polar Regions/Tropics
Moisten
Winter
Summer
Global Warming is NOT Uniform
• Arctic warms up the most 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) will
get drier and wet areas (e.g., British
Columbia) will get wetter.
Uncertainty: Get Used to It!
• Considerable uncertainty regarding
global temperature changes (roughly
1.5 to 4 C)
• Even more uncertainty for local
changes
• Uncertainty has not lessened much
even with past decades of
research.
Temperature Change in the NW
Figure 1. Average annual temperature change for the Pacific Northwest (in °F, relative to the 1901–1960 average). The dashed line is the
fitted trend.ii
Climate Change in NW
• Temperatures have warmed by about 1 F
over the past 120 years.
• This warming appears to have been
occurring over the entire period, with
short-term excursions due to natural
variability (e.g., the Pacific Decadal
Oscillation, PDO)
• There is no discernable trend in
precipitation.
Warming in the Northwest
• It appears that there has been little
human-caused warming in most of the
Northwest so far.
• This makes a lot of sense--our weather
has controlled by the Pacific and the
eastern Pacific is one of the last places
that will warm significantly.
• Global warming will be weaker and
delayed here…but it will happen in force
by the end of the century.
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
Cascade snowpack hasn’t changed in
the last 30 years
Future of 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?
Advice: Don’t buy this after 2050!
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 reason
to expect stronger storms 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 move northward.
• It is possible that storms here might
WEAKEN under global warming.
Extreme Claims
• Greenhouse warming “advocacy” groups
and some activist scientists have been
making unfounded claims that individual
extreme weather events are undoubtedly
the effects of global warming.
• The media highlight such reports as if they
were true.
• Many are not.
New Study by Professor
Elizabeth Barnes of Colorado
State
“Using the Coupled Model Intercomparison Project, phase 5 multimodel
ensemble, we demonstrate that climate models consistently project a decrease
in the frequency and persistence of the westward flow that led to Sandy’s
unprecedented track, implying that future atmospheric conditions are less likely
than at present to propel storms westward into the coast.”
Claims That Extreme Events
are the Result of Global
Warming are Often
Unsupported by the Facts
Texas Temperatures
No Real Trend
IPCC Report on Extremes:
Quite Moderate
Finally, does the lack of
warming during the last ten
year’s mean anything?
No, one should expect this.
• 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 expect some short period when
natural cooling balances out global
warming.
• Eventually, global warming wins.
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
Milankovitch Cycles
Eccentricity of Earth’s Orbit
• Varies over 10s of thousands of years
Obliquity and Precession
Fig. 14-12, p. 396
Periodic Ice Ages
Can We Stop the Next Ice Age
The End