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

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
Summer Winter

Global Warming in Northwest
• It appears that there has been very little warming here in 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
+0.6
+0.8
+1.0
+1.2
+1.4
Air Temperature Trend (1979-2005)

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!

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 of Earth’s Orbit
• Varies over 10s of thousands of years

Obliquity and Precession

Axis now
Axis in approximately
11,000 years
January
23 1/2 °
(b) Conditions now
July
(a)
July
January
(c) Conditions in about 11,000 years
Editable Text
Fig. 14-11, p. 395

Fig. 14-12, p. 396

Variations in Solar Radiation

Periodic Ice Age

Can We Stop the Next Ice Age

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
• 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 s tream --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.

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 is very serious business.
• Global warming will be delayed here.
• Our main issue will be loss of snowpack and summer water supply.
• Don’t believe all the hype and false information being given by both “sides.”

The End