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UCSD COSMOS 2012:
Living Oceans and Climate Change
Prof. Lynn Russell (lead instructor)
Dr. Ngai Chin Lai (co-instructor)
Prof. Joel Norris (co-instructor)
Ms. Megan Jones (teacher fellow)
Ms. Amanda Frossard (cluster assistant)
Mr. Khalid Azizi (cluster assistant)
Course websites
http://aerosols.ucsd.edu/cosmos.html
http://meteora.ucsd.edu/~jnorris/cosmos/cosmos.html
PowerPoint lectures and other materials will be made
available on the course websites
Albedo,
Greenhouse Effect,
and
Global Warming
Unless otherwise noted, figures and
illustrations come from the Fourth Report
(AR4) by the Intergovernmental Panel on
Climate Change (IPCC).
Visible light, infrared (IR),
ultraviolet (UV), X-rays, γ-rays,
microwaves, and radio are all
forms of electromagnetic
radiation
Sun
Each type has a different
wavelength (λ).
Earth
The shorter the wavelength, the
greater the energy of individual
photons
Shortest to longest wavelength:
γ-rays, X-rays, UV, visible, IR,
microwave, radio
Does infrared radiation
easily go through glass?
Earth’s Energy Budget
• Earth absorbs visible and near IR radiation from the Sun
• Earth emits thermal infrared radiation back to space
• Certain constituents reduce emission to space
Sun
Earth
Start CO2 in jar
Solar Radiation
• Solar radiation flux at the average distance of Earth’s
orbit (S0) is about 1367 W m-2
(This is equivalent to ?? 60W light bulbs every square
meter)
• This solar radiation intersects with πR2 area, where R is
the radius of the Earth
Solar Radiation
• The total energy rate for solar radiation intersecting
Earth is S0 πR2
• The global surface area of Earth is 4πR2
• What is the average amount of solar radiation per m2
spread out over the Earth? (S0 = 1367 W m-2)
Solar Radiation
• Global average solar radiation flux at the top of the
atmosphere: S0 / 4 = 342 W m-2
(This is equivalent to ?? 60W light bulbs every square
meter)
• How much is directly reflected back?
• How much is absorbed by the Earth and atmosphere?
• What happens to absorbed radiation?
• In equilibrium, how much radiation is emitted by the
Earth?
What happens to visible light
when it arrives at the Earth?
How does heat leave the
surface of the Earth?
Look outside.
Jars go outside.
Planetary Albedo
• Planetary albedo αp is the global average fraction of
solar radiation reflected back to space.
• Earth’s planetary albedo is 0.31
• The global average value of reflected solar flux is αp S0 /
4 = 107 W m-2
• The global average value of absorbed solar flux is (1 –
αp) S0 / 4 = 235 W m-2
Various Albedo Values
•
•
•
•
•
Ocean albedo is about 0.1 (except for sunglint)
Sandy desert albedo is about 0.25-0.35
Forest albedo is about 0.15
Snow/ice albedo is about 0.6-0.9
Cloud albedo is about 0.3-0.6
Greenhouse Effect
• The reduction in the amount of energy leaving the Earth
caused by clouds and greenhouse gases acts like a
blanket to keep the Earth warmer
• Clouds and greenhouse gases also emit IR radiation
toward the surface (324 W m-2)
• The surface absorbs this additional radiation and thus is
kept warmer
Greenhouse Effect
• The strongest greenhouse gas is water vapor
• The next strongest greenhouse gas is CO2
• Clouds (composed of liquid water droplets and ice
crystals) have a greenhouse effect and an albedo effect
• High clouds have the strongest greenhouse effect
because they are coldest
Check jars
Earth’s Radiation Budget
• What will happen if absorbed solar radiation is out of
balance with emitted thermal radiation?
• What can cause imbalances?
Importance of Albedo
• All else held the same, a doubling of CO2 in the
atmosphere (280 ppm  560 ppm) will reduce outgoing
IR by about 4 W m-2
• This is roughly equivalent to the change in absorbed
solar radiation caused by a 0.01 change in planetary
albedo
0.01 x 342 W m-2 = 3.4 W m-2
• Small changes in albedo can have a big effect on climate
human activity
natural state
measured
global warming
of Earth’s surface
primarily caused by
anthropogenic
increase in
greenhouse gases
temperature
variations
estimated
from tree rings
and other
proxy records
measured
temperature
change
Thermal Inertia
• The change in temperature caused by radiative
imbalance does not occur instantaneously due to
thermal inertia
• It takes decades to centuries for the ocean to warm up or
cool down
• We have not yet experienced the full warming that will be
produced by the CO2 we have already put into the
atmosphere
Positive Feedbacks
• Two processes will very likely increase the warming
initially produced by additional CO2
Ice Albedo Feedback
• Warmer temperature will cause ice sheets and snow to
melt back
• The surface will become darker and absorb more solar
radiation
• This will cause temperature to increase even more
Water Vapor Feedback
• Warmer temperature will cause more water to evaporate
and enter the atmosphere
• More water vapor in the atmosphere will reduce the
amount of IR radiation emitted to space
• This will cause temperature to increase even more
Check jars
Describe Jar Experiment