What is the Greenhouse Effect?
Review of last lecture
– What is energy? 3 methods of energy transfer
– The names of the 6 wavelength categories in the
–
–
–
electromagnetic radiation spectrum
The wavelength range of Sun (shortwave) and
Earth (longwave) radition
The two basic motions of the Earth
What causes the four seasons: the 23.5 degree
tilt of the Earth’s axis, and the 3 ways it affects
the solar insolation (change of length of the day,
beam spreading, beam depletion)
Satellite Measurements of the Earth’s
Radiation Budget
NASA’s Earth Radiation
Budget Satellite (ERBS)
1985-1989
Earth’s energy budget (averaged over the
whole globe and over a long time
Yellow:
shortwave
Red:
longwave
Sensible
heat 7%
Net Longwave 21%
Latent heat
23%
• At the top of the atmosphere:
•
Incoming shortwave = Reflected Shortwave + Emitted longwave
At the surface:
Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming)
+ Latent heat flux + sensible heat flux
Atmospheric influences on radiation
Reflection
Scattering
Absorption
(absorber
warms)
Atmospheric Absorption - The Greenhouse Effect
Transparent
to solar
(shortwave)
radiation
Opaque to
earth’s
(longwave)
radiation
Major GH gases:
CO2, H20(v), CH4
Recent change of greenhouse gases
Deuterium
(Temperature)
• Global atmospheric concentrations of CO2 and CH4 have increased
markedly as a result of human activities since 1750 and now far
exceed pre-industrial values determined from ice core
measurements spanning the last 650,000 years!
The importance of methane (CH4)
• 23 times more powerful as a
greenhouse gas than CO2
• The livestock sector is a major
player, which accounts for 35-40%
global anthropogenic emissions of
methane (their burps!)
• The livestock sector is responsible
for 18% of total greenhouse gas
emissions
• Therefore, consuming less meat
can help reducing global warming
than not driving cars.
Video: The greenhouse effect
• http://www.youtube.com/watch?v=ZzCA60Wno
Mk
Atmospheric Scattering
3 Types of Scattering:
1.
2.
3.
Raleigh
Mie
Non-Selective
A discussion of each type follows…
Rayleigh Scattering
•
•
•
involves gases smaller than insolation wavelength
scatters light in all directions
most effective at short wavelengths (violet, blue)…
hence, blue sky
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, Sunrise
2) Mie scattering
– involves aerosols (e.g. dust, smoke) larger
than gas molecules
– forward scatter
– equally effective across visible spectrum
– explains hazy, gray days
3) Non-selective scattering
– Happens when atmospheric particles are much larger than the
wavelength of incoming radiation (e.g. water droplets in clouds)
– Act like lenses; scatter all wavelengths equally to create a white
appearance
– That’s why clouds appear white
Surface sensible and latent heat fluxes
• Both are turbulent (noisy) fluxes related to conduction and
•
•
•
•
convection.
Both proportional to surface wind speed.
Sensible heat flux is dry flux from warm to cold regions
Latent heat flux (also called evaporation) is wet flux from
wet to dry regions
Important for hurricane amplification
Surface Wind
From
NOAA
ESRL
Summary: Earth’s energy budget
Yellow:
shortwave
Red:
longwave
Sensible
heat 7%
Net Longwave 21%
Latent heat
23%
• At the top of the atmosphere:
•
Incoming shortwave = Reflected Shortwave + Emitted longwave
At the surface:
Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming)
+ Latent heat flux + sensible heat flux
Summary
• Earth’s energy balance at the top of the atmosphere
•
•
•
•
and at the surface. What percentage of solar energy is
absorbed by the surface?
Atmospheric influences on radiation (3 ways)
What cause the greenhouse effect? What are the major
greenhouse gases? Why is methane important?
The three types of atmospheric scattering. What causes
the blue sky? Why causes the reddish-orange sunsets?
Sensible heat flux (dry flux from warm to cold regions)
and latent heat flux (wet flux from wet to dry regions).
Both proportional to surface wind speed