What is the Greenhouse Effect?

Review of last lectureReview of last lecture

– What is energy? 3 methods of energy What is energy? 3 methods of energy transfertransfer

– The names of the 6 wavelength categories The names of the 6 wavelength categories in the electromagnetic radiation spectrumin the electromagnetic radiation spectrum

– The wavelength range of Sun (shortwave) The wavelength range of Sun (shortwave) and Earth (longwave) raditionand Earth (longwave) radition

– The two basic motions of the EarthThe two basic motions of the Earth– What causes the four seasons: the 23.5 What causes the four seasons: the 23.5

degree tilt of the Earthdegree tilt of the Earth’’s axis, and the 3 s axis, and the 3 ways it affects the solar insolation (change ways it affects the solar insolation (change of length of the day, beam spreading, of length of the day, beam spreading, beam depletion)beam depletion)

Satellite Measurements of the Satellite Measurements of the EarthEarth’’s Radiation Budgets Radiation Budget

NASA’s Earth Radiation Budget Satellite (ERBS) 1985-1989

EarthEarth’’s energy budget (averaged over s energy budget (averaged over the whole globe and over a long timethe whole globe and over a long time

• At the top of the atmosphere: At the top of the atmosphere: Incoming shortwave = Reflected Shortwave + Emitted longwaveIncoming shortwave = Reflected Shortwave + Emitted longwave• At the surface:At the surface: Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) + Latent heat flux + sensible heat flux+ Latent heat flux + sensible heat flux

Sensible heat 7%

Latent heat 23%

Net Longwave 21%

Yellow: shortwave

Red: longwave

Atmospheric influences on Atmospheric influences on radiationradiation

ReflectionReflection ScatteringScattering Absorption Absorption (absorber (absorber warms)warms)

Atmospheric Absorption - The Greenhouse EffectAtmospheric Absorption - The Greenhouse Effect

Transparent Transparent to solar to solar (shortwave) (shortwave) radiationradiation

Opaque to Opaque to earthearth’’s s (longwave) (longwave) radiationradiation

Major GH gases: CO2, H20(v), CH4

Recent change of greenhouse gasesRecent change of greenhouse gases

• Global atmospheric concentrations of COGlobal atmospheric concentrations of CO22 and CH and CH44 have have increased markedly as a result of human activities since 1750 increased markedly as a result of human activities since 1750 and now and now far exceedfar exceed pre-industrial values determined from ice pre-industrial values determined from ice core measurements spanning the last core measurements spanning the last 650,000650,000 years!years!

Deuterium (Temperature)

The importance of methane The importance of methane (CH(CH44))

• 23 times more powerful as a 23 times more powerful as a greenhouse gas than COgreenhouse gas than CO22

• The livestock sector is a major The livestock sector is a major player, which accounts for 35-player, which accounts for 35-40% global anthropogenic 40% global anthropogenic emissions of methane (their emissions of methane (their burps!)burps!)

• The livestock sector is The livestock sector is responsible for 18% of total responsible for 18% of total greenhouse gas emissionsgreenhouse gas emissions

• Therefore, consuming less meat Therefore, consuming less meat can help reducing global can help reducing global warming than not driving cars.warming than not driving cars.

Video: The greenhouse effectVideo: The greenhouse effect• http://www.youtube.com/watch?v=ZzCA60WnoMk

3 Types of Scattering: 3 Types of Scattering: 1.1. RaleighRaleigh

2.2. MieMie

3.3. Non-SelectiveNon-Selective

Atmospheric Atmospheric ScatteringScattering

A discussion of each type follows…A discussion of each type follows…

• involves gases smaller than insolation wavelength• scatters light in all directions • most effective at short wavelengths (violet, blue)

… hence, blue sky

Rayleigh Scattering Rayleigh Scattering

The Earth has an atmosphere. So it has Rayleigh scattering and its sky appears blue

The Moon has no atmosphere. So it has no Rayleigh scattering and its sky appears dark

• Rayleigh scattering also explains reddish-orange sunsets when light travels through thick slice of atmosphere

Monet: Impressions, SunriseMonet: Impressions, Sunrise

2) Mie scattering2) Mie scattering– involves aerosols (e.g. dust, smoke) involves aerosols (e.g. dust, smoke)

larger than gas moleculeslarger than gas molecules– forward scatterforward scatter– equally effective across visible spectrumequally effective across visible spectrum– explains hazy, gray daysexplains hazy, gray days

3) Non-selective scattering3) Non-selective scattering– Happens when atmospheric particles are much larger Happens when atmospheric particles are much larger

than the wavelength of incoming radiation (e.g. water than the wavelength of incoming radiation (e.g. water droplets in clouds)droplets in clouds)

– Act like lenses; scatter all wavelengths equally to create Act like lenses; scatter all wavelengths equally to create a white appearancea white appearance

– ThatThat’’s why clouds appear whites why clouds appear white

Surface sensible and latent heat Surface sensible and latent heat fluxesfluxes

• Both are turbulent (noisy) fluxes related to conduction Both are turbulent (noisy) fluxes related to conduction and convection. and convection.

• Both proportional to surface wind speed.Both proportional to surface wind speed.

• Sensible heat flux is dry flux from warm to cold regionsSensible heat flux is dry flux from warm to cold regions

• Latent heat flux (also called evaporation) is wet flux Latent heat flux (also called evaporation) is wet flux from wet to dry regionsfrom wet to dry regions

• Important for hurricane amplificationImportant for hurricane amplification

From NOAA ESRL

Surface Wind

Summary: EarthSummary: Earth’’s energy budgets energy budget

• At the top of the atmosphere: At the top of the atmosphere: Incoming shortwave = Reflected Shortwave + Emitted longwaveIncoming shortwave = Reflected Shortwave + Emitted longwave• At the surface:At the surface: Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) + Latent heat flux + sensible heat flux+ Latent heat flux + sensible heat flux

Sensible heat 7%

Latent heat 23%

Net Longwave 21%

Yellow: shortwave

Red: longwave

SummarySummary

• EarthEarth’’s energy balance at the top of the s energy balance at the top of the atmosphere and at the surface. What percentage atmosphere and at the surface. What percentage of solar energy is absorbed by the surface?of solar energy is absorbed by the surface?

• Atmospheric influences on radiation (3 ways)Atmospheric influences on radiation (3 ways)

• What cause the greenhouse effect? What are the What cause the greenhouse effect? What are the major greenhouse gases? Why is methane major greenhouse gases? Why is methane important? important?

• The three types of atmospheric scattering. What The three types of atmospheric scattering. What causes the blue sky? Why causes the reddish-causes the blue sky? Why causes the reddish-orange sunsets? orange sunsets?

• Sensible heat flux (dry flux from warm to cold Sensible heat flux (dry flux from warm to cold regions) and latent heat flux (wet flux from wet regions) and latent heat flux (wet flux from wet to dry regions). Both proportional to surface wind to dry regions). Both proportional to surface wind speedspeed