Download Lecture 2: Energy Balance - San Jose State University

METR112 Global Climate Change -- Lecture 2 Energy Balance
Prof. Menglin Jin
San Jose State University
Review Lecture 1
1. Two critical increases – global mean surface temperature and
greenhouse gases
2. One key concept – greenhouse effect
Change in surface temperature in 20th century
Two main points in this figure
• Global mean surface temperatures have
increased 0.5-1.0°C since the late 19th
century
• The 20th century's 10 warmest years all
occurred in the last 15 years of the century
Note: 1. why is global mean?
2. what is surface air temperature? (see next few slides)
The “Keeling curve,” a long-term record of atmospheric CO2
concentration measured at the Mauna Loa Observatory (Keeling et al.).
Although the annual oscillations represent natural, seasonal variations,
the long-term increase means that concentrations are higher than
they have been in 400,000 years.
Graphic courtesy of NASA’s Earth Observatory.
Methane
Greenhouse gases (important!)
CO2
CH4
N2O (Nitrous Oxiode, so called “laughing gas”)
CFC
O3
H2O
by the early 21st century,
N2O had become nearly as important a greenhouse gas as methane.
Their best guess was 0.7°C for N2O, and 0.3°C for methane. Wang et al. (1976).
The Greenhouse Effect (Important concept)
Energy of Earth
BALANCED
BALANCED
BALANCED
BALANCED
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%20Librarywmv/energy%20balance/
Earth’s Energy Budget.WMV
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
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
Unit Review
• What is the current temperature in ºC?
(current temp = 90F)
• 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?
Answer: statistical averaged
speed of air molecules
•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
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.
All cell phones, once powered on, emit certain amounts of
electromagnetic radiation in the microwave radio frequency range.
eport that associated prolonged mobile phone use and exposure to differing
amounts of cellular phone radiation to brain tumors, cancer, stress, headaches,
cognitive problems, and sleep disorders
http://heatexchanger-design.com/2011/03/17/radiation-2/
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
What forms you see here to transfer heat?
Video Global Energy Balance Albedo
See video below to help your understanding
http://www.met.sjsu.edu/metr112-videos/MET%20112%20Video%20Library-wmv/energy%20balance-albedo/
a. Ice Albedo .wmv
b. Clouds albedo.wmv -observe cloud and surface albedo,
also observe shortwave radiation and lonwave radiation
c. Globe Ice Albedo.wmv
Video Global Energy Balance
What is the source of global energy?
What is the difference between icesheet and
ocean in terms of their reflections on
incoming solar radiation?
Arctic sea ice coverage, 1979 and 2003, all students need to read
NASA http://www.learner.org/channel/courses/envsci/unit/text.php?unit=12&secNum=7
Albedo Definition
The ratio of the outgoing solar radiation reflected by
an object to the incoming solar radiation incident upon it.
By Earth Observatory Glossary, NASA
http://earthobservatory.nasa.gov/Library/glossary.php3?mode=all
I IN
α=
IOUT
IIN
IOUT
IIN: Incoming solar radiation reaching the object
Iout: Reflected solar radiaiton by the surface
By Reading
NASA http://www.learner.org/channel/courses/envsci/unit/text.php?unit=12&secNum=7/
we can see:
• The Earth is not warming uniformly.
• 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
(Important!)
Smaller albedo
More insolation in surface
Higher surface temperature
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.
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 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.
Why Is Surface Albedo Critical?
Surface Energy Budget:
(1-α)Sd +LWd-εσTskin4 +SH+LE + G= 0
Surface albedo
Answer: albedo plays the key role in surface energy balance as it decides
how much surface insolation is kept in Earth surface system
Albedo= 0.0 indicates that the surface absorbs all solar
radiation,
Albedo = 1.0 means that the surafce reflects all solar
radiation
Albedo and Cool Roofs
Cool roof needs
• High/Low albedo
• High/Low emissivity
Handout: albedo and cool roofs
http://theothermy.blogspot.com/2007/12/albedo-and-cool-roofs.html
NASA MODIS-Observed Albedo (0.3-5.0mm)
For 14 - 29 September, 2001
No Data
0.0
0.2
0.4+
NASA MODIS Observed Albedo (0.3-5.0mm)
For 1 - 16 January, 2002
No Data
0.0
0.2
0.4+
NASA MODS-Observed Albedo (0.3-5.0mm)
For 7 - 22 April, 2002
No Data
0.0
0.2
0.4+
Conclusion from NASA MODIS
Albedo (namely, the last few slides)
• Albedo varies across the global land
surfaces. This is determined by land cover
• Albedo has clear seasonality
• Snow surafce has high albedo, forest has
low albedo, desert has high albedo