METR112 Global Climate Change -- Lecture 2 Energy Balance and
Prof. Menglin Jin
San Jose State University
Surface Albedo
Video Greenhouse Effect
___CO2, H20______ (CO2, H2O, N2, O2)
in Atmosphere _____ (absorb, penetrate)
solar energy, and _______ (absorb,
penetrate) longwave surface energy. This
______ (extracting, leaving) longwave
energy is called ______ (greenhouse
effect, albedo effect)
Video: Global Ice Albedo
http://www.met.sjsu.edu/metr112-videos/MET%20112%20Video%20Library-MP4/energy%20balance-albedo/
Global Ice Albedo.mp4
Ice Albedo.mp4
Arctic sea ice coverage, 1979 and 2003
NASA http://www.learner.org/channel/courses/envsci/unit/text.php?unit=12&secNum=7
•The Earth is not warming uniformly.
•Notably, climate change is expected to affect the polar
regions more severely:
•The Arctic is warming nearly twice as rapidly as the rest of the world;
•winter temperatures in Alaska and western Canada have risen by up to 3–4°C
in the past 50 years, and
•Arctic precipitation has increased by about 8 percent over the past century
(mostly as rain)
Less snow
Due to, partly:
Positive albedo feedback
Smaller albedo
More insolation in surface
Higher surface temperature
Albedo Definition
The ratio of the outgoing solar radiation reflected by
an object to the incoming solar radiation incident upon it.
Earth Observatory Glossary
By NASA,
Responsible NASA official: Dr. Michael D. King,
http://earthobservatory.nasa.gov/Library/glossary.php3?mode=al
I IN
α=
IOUT
IIN
IOUT
Albedo of Earth
•The term albedo (Latin for white) is commonly used to or
applied to the overall average reflection of an object.
•the albedo of the Earth is 0.39 (Kaufmann 1991 ) and
this affects the equilibrium temperature of the Earth.
•The greenhouse effect, by trapping infrared radiation,
can lower the albedo of the earth and cause global warming.
This is why GHG is important
This is why albedo is important
Features of Albedo
•Dimensionless
•Range: 0 (dark) – 1 (bright)
The word is derived from Latin albedo "whiteness", in turn from albus "white".
•Albedo depends on wavelength
•Albedo is determined by the structural and optical properties
of the surface, such as shadow-casting, mutiple scattering, mutual shadowing,
transmission, reflection, absorption and emission by surface elements,
facet orientation distribution and facet density.
•Albedo depends on view angle
Why Is Surface Albedo Critical?
Surface Energy Budget:
(1-α)Sd +LWd-εσTskin4 +SH+LE + G= 0
Answer: albedo plays the key role in surface energy balance as it decides
how much surface insolation is kept in Earth surface system
This is a black spruce forest in the BOREAS experimental region in Canada.
Left: backscattering (sun behind observer), note the bright region (hotspot)
where all shadows are hidden. Right: forwardscattering (sun opposite observer),
note the shadowed centers of trees and transmission of light through
the edges of the canopies. Photograph by Don Deering.
http://www-modis.bu.edu/brdf/brdfexpl.html
A soybean field. Left: backscattering (sun behind observer). Right: forwardscattering
(sun opposite observer), note the specular reflection of the leaves.
Photograph by Don Deering. http://www-modis.bu.edu/brdf/brdfexpl.html
Wet and dry surfaces have different albedo
Albedo is function of wavelength.
Boradband albedo
Boradband albedo is the integrated value of spectral emissivity at all wavelength
Spectral albedo – the reflectivity for specific wavelength
An albedo value of 0.0 indicates that the surface absorbs
all solar radiation, and a 1.0 albedo value represents total reflectivity.
http://theothermy.blogspot.com/2007/12/albedo-and-cool-roofs.html
CMG Broadband White-Sky Albedo (0.3-5.0mm)
14 - 29 September, 2001
No Data
0.0
0.2
0.4+
CMG Broadband White-Sky Albedo (0.3-5.0mm)
1 - 16 January, 2002
No Data
0.0
0.2
0.4+
CMG Broadband White-Sky Albedo (0.3-5.0mm)
7 - 22 April, 2002
No Data
0.0
0.2
0.4+
Snow versus Non-snow Albedos 40–50°N Nov 00–Jan 01
Jin et al., How does Snow Impact the Albedo of Vegetated Land Surfaces as Analyzed with MODIS
Data?, in press, Geophys. Res. Let., 2002
Snow albedo is higher than non-snow albedo
Video: Snow Albedo Feedback
http://www.met.sjsu.edu/metr112-videos/MET%20112%20Video%20Library-MP4/energy%20balance-albedo/
Albedo-1.mp4
Energy of Earth
Useful link on energy balance:
http://earthguide.ucsd.edu/earthguide/diagrams/energybalance/index.html
Energy Balance video
http://www.met.sjsu.edu/metr112videos/MET%20112%20Video%20LibraryMP4/energy%20balance/
Earth’s Energy Budget.mp4
100% of the incoming energy from the sun is balanced by
100% percent total energy outgoing from the earth.
incoming energy from the Sun = outgoing energy from the Earth.
Units
• Our class will use both English and Metric unit systems.
• Most important:
– Distance (kilometres and miles)
– Temperature (ºC and ºF)
• Conversions:
1.6 km = 1 mile; 1 km = 0.61 miles
(9/5 x ºC) + 32 = ºF
(ºF – 32) x 5/9 = ºC
Class participation (2)
Unit Review
• What is the current temperature in ºC?
(current temp = 52F)
• California is about 800 miles long (from
Oregon to Mexico). How many
kilometers is that?
• If you were told that the average high
temperature in Sydney Australia at this
time of year is 26ºC, what temperature is
that in ºF?
Three temperature scales:
•Kelvin
•Celsius °K= °C+273
•Fahrenheit
•What does temperature
mean physically?
•What does 0° K mean?
Temperature
the degree of hotness or coldness of a body or environment
(corresponding to its molecular activity)
Temperature is one of the principal parameters of thermodynamics.
On the microscopic scale, temperature is defined as the average energy of
microscopic motions of a single particle in the system per degree of freedom.
On the macroscopic scale, temperature is the unique physical property that
determines the direction of heat flow between two objects placed in thermal contact.
Cold temperature
Warm temperature
Just an example, could be higher or lower
Energy Balance
• Assume that the
Earth’s surface is in
thermodynamic
equilibrium:
• Thermodynamic
Equilibrium:
– The flow of energy
away the surface
equals the flow of
Surface
energy toward the
Average surface temperature = 15°C
surface
http://en.wikipedia.org/wiki/Solar_radiation#Climate_effect_of_solar_radiation
since the Earth is much cooler than the Sun, its radiating energy is much weaker
(long wavelength) infrared energy. energy radiation into the atmosphere as heat,
rising from a hot road, creating shimmers on hot sunny days.
The earth-atmosphere energy balance is achieved as the energy received from the Sun
balances the energy lost by the Earth back into space.
So, the Earth maintains a stable average temperature and therefore a stable climate.
http://www.srh.noaa.gov/jetstream//atmos/energy.htm
Group Discussion
If you go camping with friends. The first day
and night are clear and the 2nd day and
night are cloudy.
• Which day is cold?
• Which night is cold?
• Why?
The Transfer Of Heat: 3 ways
The heat source for our planet is the sun
Energy from the sun is transferred through space and through the earth's atmosphere
to the earth's surface.
Since this energy warms the earth's surface and atmosphere,
some of it is or becomes heat
energy.
There are three ways heat is transferred into and through the atmosphere:
radiation
conduction
convection
Radiation is the transfer of heat energy through space by electromagnetic radiation.
The flow of heat by conduction occurs via collisions between atoms and
molecules in the substance and the subsequent transfer of kinetic energy.
Take a look: http://www.nationmaster.com/encyclopedia/Image:Translational-motion.gif
Fig. 2-2, p. 30
Cumulus clouds indicates where upward convection currents are
Convection is the transfer of heat energy in a fluid.
Other example:
In kitchen liquid boiling