The Greenhouse EffectThe Greenhouse Effect

A quick reviewA quick review

The Greenhouse EffectThe Greenhouse Effect

• A natural process that keeps the A natural process that keeps the surface of the earth at a habitable surface of the earth at a habitable temperature.temperature.– Without the greenhouse effect, surface Without the greenhouse effect, surface

temperatures would be about 60º F temperatures would be about 60º F colder. colder.

– There would be NO liquid water!There would be NO liquid water!

How does it work?How does it work?

Image source: kids.earth.NASA.gov

How does it work?How does it work?• Short wavelength (ultraviolet) radiation Short wavelength (ultraviolet) radiation

from Sun reaches Earthfrom Sun reaches Earth

• Earth warms and emits long wavelength Earth warms and emits long wavelength (infrared) radiation back towards space(infrared) radiation back towards space

• Greenhouse gases in Earth’s atmosphere Greenhouse gases in Earth’s atmosphere “trap” some of the infrared radiation near “trap” some of the infrared radiation near EarthEarth– Think of your car on a sunny day: the sunlight Think of your car on a sunny day: the sunlight

enters through the closed windows and warms enters through the closed windows and warms the car interior. That heat can’t escape back the car interior. That heat can’t escape back out through the glass.out through the glass.

What are the main What are the main Greenhouse Gases?Greenhouse Gases?

Water vapor (HWater vapor (H22O)O)

Carbon dioxide (COCarbon dioxide (CO22))

Methane (CHMethane (CH44))

Nitrous oxide (NNitrous oxide (N22O)O)

These were all present in atmosphere These were all present in atmosphere before humans, but we are adding morebefore humans, but we are adding more

Greenhouse Greenhouse Gases allow Gases allow ~75% of short ~75% of short wavelength wavelength energy from energy from Sun to reach Sun to reach Earth.Earth.

Only 15-30% Only 15-30% of the energy of the energy re-radiated by re-radiated by Earth escapes Earth escapes back through back through greenhouse greenhouse gases in the gases in the atmosphere.atmosphere.

Image created by Robert A. Rohde / Global Warming Art

http://www.globalwarmingart.com/wiki/File:Atmospheric_Transmission_png

Greenhouse Gas EfficiencyGreenhouse Gas EfficiencyGasGas Relative Relative

greenhouse greenhouse efficiency per efficiency per molecule molecule

Concentration Concentration in the in the atmosphere atmosphere (ppm) (ppm)

Relative Relative efficiency x efficiency x concentration concentration (ppm) (ppm)

Carbon Carbon Dioxide (CODioxide (CO22))

11 350350 350350

Methane (CHMethane (CH44)) 3030 1.71.7 5151Nitrous Oxide Nitrous Oxide (N(N22O)O)

160160 0.310.31 49.649.6

Ozone (OOzone (O33)) 20002000 0.060.06 120120ChlorofluoroChlorofluorocarbons carbons (CFCs)(CFCs)

21,00021,000 0.000260.00026 5.465.46

Anthropogenic Greenhouse Anthropogenic Greenhouse Gas SourcesGas Sources

Water (HWater (H22O)O)– sources largely natural, sources largely natural,

but large amounts but large amounts added during rocket added during rocket launcheslaunches

Carbon Dioxide (COCarbon Dioxide (CO2)2)

– Burning fossil fuels Burning fossil fuels (cars, factories, power (cars, factories, power plants, etc.)plants, etc.)

– Burning forests (landuse Burning forests (landuse conversion)conversion)

– Rocket launchesRocket launches

Anthropogenic Greenhouse Anthropogenic Greenhouse Gas SourcesGas Sources

Methane (CHMethane (CH44))– Enteric fermentation Enteric fermentation

(cow burps!)(cow burps!)– Landfill emissionsLandfill emissions– Rice cultivationRice cultivation– Natural gas useNatural gas use– Melting of permafrost in Melting of permafrost in

ArcticArctic

Nitrous Oxide (NNitrous Oxide (N22O)O)– Agricultural processes Agricultural processes

(fertilizers)(fertilizers)

Buuurp!

Anthropogenic Greenhouse Anthropogenic Greenhouse Gas SourcesGas Sources

What about CFCs?What about CFCs?

Very powerful Very powerful greenhouse gas, greenhouse gas, but people have but people have been very been very successful at successful at reducing emissions reducing emissions (Montreal Protocol)(Montreal Protocol)

Effect on Upper AtmosphereEffect on Upper Atmosphere

• The Greenhouse Effect causes The Greenhouse Effect causes warmingwarming at Earth’s surface, but at Earth’s surface, but coolingcooling in upper atmosphere in upper atmosphere– If more of Earth’s emitted longwave If more of Earth’s emitted longwave

radiation is held close to the surface, it radiation is held close to the surface, it is not available to cause warming in the is not available to cause warming in the upper atmosphereupper atmosphere

– More noctilucent cloud formation in the More noctilucent cloud formation in the Mesosphere? Mesosphere? (see “Noctilucent Clouds.ppt”)(see “Noctilucent Clouds.ppt”)