METR112 Global Climate Change -- Lecture 2 Energy Balance

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METR112 Global Climate Change -- Lecture 2
Energy Balance
Prof. Menglin Jin San Jose State University
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Review Lecture 1

• Two critical increases global mean surface
  temperature and
• greenhouse gases
• 2. One key concept greenhouse effect

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Change in surface temperature in 20th century
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Two main points in this figure

• Global mean surface temperatures have increased
  0.5-1.0C 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)
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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 NASAs Earth Observatory.
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Methane
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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 0.7C for
N2O, and 0.3C for methane. Wang et al. (1976).
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The Greenhouse Effect (Important concept)
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Energy of Earth
BALANCED
BALANCED
BALANCED
BALANCED
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Useful link on energy balance
http//earthguide.ucsd.edu/earthguide/diagrams/ene
rgybalance/index.html
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Energy Balance Video

• http//www.met.sjsu.edu/metr112-videos/MET201122
  0Video20Library-wmv/energy20balance/
• Earths Energy Budget.WMV

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Energy Balance

• Assume that the Earths surface is in
  thermodynamic equilibrium
• Thermodynamic Equilibrium
• The flow of energy away the surface equals the
  flow of energy toward the surface

Surface
Average surface temperature 15C
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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.
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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

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Unit Review
Class participation

• 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?

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• Three temperature scales
• Kelvin
• Celsius
• Fahrenheit
• What does temperature mean physically?
• What does 0 K mean?

K C273
Answer statistical averaged speed of air
molecules
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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.
Warm temperature
Cold temperature
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Just an example, could be higher or lower
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http//en.wikipedia.org/wiki/Solar_radiationClima
te_effect_of_solar_radiation
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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.ht
m
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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?

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The Transfer Of Heat 3 ways
The heat source for our planet is the 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 convect
ion
sun
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Radiation is the transfer of heat energy through
space by electromagnetic radiation.
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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/radiati
on-2/
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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/encyclope
dia/ImageTranslational-motion.gif
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Fig. 2-2, p. 30
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Cumulus clouds indicates where upward convection
currents are
Convection is the transfer of heat energy in a
fluid.
Other example
In kitchen liquid boiling
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What forms you see here to transfer heat?
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Video Global Energy Balance -Albedo
See video below to help your understanding http/
/www.met.sjsu.edu/metr112-videos/MET2011220Video
20Library-wmv/energy20balance-albedo/

• Ice Albedo .wmv
• Clouds albedo.wmv -observe cloud and surface
  albedo,
• also observe shortwave radiation and
  lonwave radiation
• c. Globe Ice Albedo.wmv

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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?

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Arctic sea ice coverage, 1979 and 2003, all
students need to read NASA http//www.learner.o
rg/channel/courses/envsci/unit/text.php?unit12se
cNum7
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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, NASAhttp//earthob
servatory.nasa.gov/Library/glossary.php3?modeall
IIN Incoming solar radiation reaching the
object Iout Reflected solar radiaiton by the
surface
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By Reading NASA http//www.learner.org/channel/co
urses/envsci/unit/text.php?unit12secNum7/ 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 34C in the past 50 years, and
• - Arctic precipitation has increased by about 8
  percent over the past century
• (mostly as rain)

Due to, partly
Positive albedo feedback
(Important!)
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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
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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.
  

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Why Is Surface Albedo Critical?
Surface Energy Budget
(1-a)Sd LWd-esTskin4 SHLE 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
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Albedo 0.0 indicates that the surface absorbs
all solar radiation, Albedo 1.0 means that
the surafce reflects all solar radiation

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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
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NASA MODIS-Observed Albedo (0.3-5.0mm) For 14 -
29 September, 2001
0.0 0.2 0.4
No Data
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• (0.3-5.0mm)

NASA MODIS Observed Albedo For 1 - 16 January,
2002
0.0 0.2 0.4
No Data
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• (0.3-5.0mm)

NASA MODS-Observed Albedo For 7 - 22 April, 2002
0.0 0.2 0.4
No Data
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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