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BAESI - Global Warming: Food Climate Connections

The Greenhouse EffectDr. Eugene Cordero

San Jose State University

Outline Greenhouse effect Energy Balance Activities

The Atmosphere

Principal Atmospheric Gases

GAS MASS

Nitrogen 75%

Oxygen 23%

Argon 1%

Water Vapor 0.3%

CO2 0.06%

Principal Atmospheric Gases

GAS MASS

Nitrogen 75%

Oxygen 23%

Argon 1%

Water Vapor 0.3%

CO2 0.06%

Greenhouse gases

Earth’s Energy BalanceEarth’s Energy Balance

Energy entering top of atmosphere

Energy entering the Earth’s surface

= Energy leaving top of atmosphere= Energy leaving top of atmosphere

= Energy leaving Earth’s surface= Energy leaving Earth’s surface

Solar Radiation (Sunlight)

Sunlight is primarily made up of the following:– Visible Light (44%)Visible Light (44%)– Infrared Radiation (48%)Infrared Radiation (48%)– Ultraviolet Radiation (7%)Ultraviolet Radiation (7%)

Unit: 1 m =

0.000001 m

Energy from the Sun

Obviously, the Sun provides the Earth with it’s energy. The question is, how much of the Sun’s energy does the Earth get?

Sun’s energy is either– Scattered (reflected away) or– Absorbed

Scattering happens by bouncing off – Particles in the atmosphere– Earth’s surface

Absorption happens when certain gases absorb the energy– The reality is the only certain gases absorb certain

wavelengths.

Incoming solar radiationIncoming solar radiation

Each ‘beam’ of incoming sunlight can be either:– Reflected back to space:

CloudsClouds AtmosphereAtmosphere SurfaceSurface

– Or absorbed; either by atmosphere (e.g. clouds or ozone) or Earth’s surface.

AlbedoAlbedo

Absorption of radiation

Absorption of shortwave radiation by atmospheric gas molecules is fairly weak; – most absorption of shortwave radiation occurs at the

Earth’s surface.

Most gases do not interact strongly with longwave radiation, however

– Greenhouse gas molecules absorb certain Greenhouse gas molecules absorb certain wavelengths of longwave radiation.wavelengths of longwave radiation.

Absorption of radiation in the Earth’s atmosphere

Longwave radiation is emitted from surface.

Some surface radiation escapes to space

Most outgoing longwave is absorbed in atmosphere (by greenhouse gases)

Greenhouse gases emit longwave upward and downward

Some atmospheric radiation escapes to space

Some atmospheric radiation is absorbed at the surface

Greenhouse EffectGreenhouse Effect

Sequence of steps:

1.1. Solar radiation absorbed by earth’s surface.Solar radiation absorbed by earth’s surface.

2.2. Earth gives off infrared radiation.Earth gives off infrared radiation.

3.3. Greenhouse gases absorb some of the Earth’s infrared radiation.Greenhouse gases absorb some of the Earth’s infrared radiation.

4.4. Greenhouse gases (water and CO2) give off infrared radiation Greenhouse gases (water and CO2) give off infrared radiation in all directions.in all directions.

5.5. Earth absorbs downward directed infrared radiationEarth absorbs downward directed infrared radiation

Result: warmer surface temperature

Earth’s Greenhouse Effect

Without the greenhouse effect, the surface temperature of Earth would be – Very Cold (-18°C)

Greenhouse gases play an important role in shaping climate.– More GHGs – warmer climateMore GHGs – warmer climate– Less GHGs – cooler climateLess GHGs – cooler climate

Activity

Draw a diagram showing how the earth is heated by the Sun.

Include arrows and/or lines to indicate the ‘Energy Balance” of the earth.

Energy Balance – Energy coming in and energy going out.

In your diagram, include how clouds absorb, reflect and emit energy.

1. What percentage of the sun’s radiation is a) absorbed by the Earth’s surface?b) absorbed by the atmospherec) reflected out to space?

2. What percentage of the energy received by the earth’s surface comes directly from greenhouse gas emissions?

3. If the sun’s radiation was to increase by 10%, how would the following energy units change (increase, decrease or stay the same)a) Energy gained by the Earth’s surface.b) Energy lost by the Earth’s surface.c) Energy emitted by greenhouse gases.d) Energy lost to space.

Activity 2