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

IPCC Report, 2001IPCC Report, 2001

• Which Scenario Will Mankind Follow?

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

Projected warmingin 21st century expected to begreatest over land and at most high northern latitudes

Projections of Future Changes in Climate

Precipitation Subtropics Drier, Midlatitudes/Polar Regions/Tropics

Moisten

Winter Summer

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

Fig. 14-11, p. 395

Axis now

Axis in approximately 11,000 years

January July

(b) Conditions now23 1/2°

(a)

July January

(c) Conditions in about 11,000 years

Editable Text

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 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.

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