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

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

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

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