MET 112 Global Climate Change Lecture 2

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MET 112 Global Climate Change - Lecture 2

• Greenhouse Effect Earth and Venus
• Dr. Eugene Cordero
• San Jose State University

• Outline
• Earth and Venus
• Greenhouse effect

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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

• What was todays low temperature in ºC?
• 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?
• Bonus You finally reach the summit of Mt.
  Aconcagua (22,834 ft) in Argentina. What is your
  altitude in kilometers? (3.2 ft/meter)

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

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

K C273
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The Solar System

• The nine planets

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Average Surface Temperature of Earth and Venus
Factors to consider

• Which planet is closer to the Sun?
• Which planet is more reflective?
• Which planet has a larger ability to absorb and
  retain solar energy?

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Source of Energy The Sun
Sun radiates energy Energy radiates out with
distance
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Earth and Venus
Based on solely the position of Venus and the
Earth, which planet would be warmer?
Venus
Earth
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Earth and Venus
Based on solely the position of Venus and the
Earth, which planet would be warmer?
Venus
Sunlight striking Venus is 93 stronger than
sunlight striking Earth, thus we would expect
Venus to be warmer
Earth
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Temperature Based Only on Distance to the Sun

• Based only on distance to the sun,
• Average surface temperatures would be as follows
  if the planets absorbed all of the incoming
  sunlight
• However

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Temperature Based Only on Distance to the Sun

• Based only on distance to the sun,
• Venus would be somewhat warmer than Earth
• Average surface temperatures would be as follows
  if the planets absorbed all of the incoming
  sunlight
• Earth 5C
• Venus 55C
• However

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Albedo

• Venus and Earth do not absorb all of the incoming
  sunlight
• Part of the incoming sunlight is reflected back
  into space
• Earth reflects ______
• Venus reflects ______
• Which brings up a definition

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• Venus and Earth do not absorb all of the incoming
  sunlight
• Part of the incoming sunlight is reflected back
  into space
• Earth reflects 30
• Venus reflects 70
• This leads to an important concept

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Albedo

• Albedo The fraction of light reflected by an
  object or a surface
• White objects have ___________
• Black objects have ___________

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Definition

• Albedo The fraction of light reflected by an
  object or a surface
• White objects have high albedos
• Black objects have low albedos

Increasing albedo
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Comparison of Earth and Venus
Earth
Venus
Venus is completely covered by highly reflective
clouds Earth is partially covered by clouds.
Which planet has a higher albedo?
_______________
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Comparison of Earth and Venus
Earth
Venus
Venus is completely covered by highly reflective
clouds Earth is partially covered by clouds.
Which planet has a higher albedo?
_______________
Venus
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Comparison of Earth and Venus

• Earths albedo is ____
• Venus albedo is ____

Earth absorbs
__
of the sunlight that strikes it.
Venus absorbs
__
of the sunlight that strikes it.
Lets re-examine the surface temperatures with
this information.
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Comparison of Earth and Venus

• Earths albedo is 30
• Venus albedo is 70

Earth absorbs
70
of the sunlight that strikes it.
Venus absorbs
30
of the sunlight that strikes it.
Lets re-examine the surface temperatures with
this information.
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Absorption of Solar Radiation Taking into Account
Distance to Sun and Albedo

• Let intensity of sunlight striking Earth be
  denoted by 100
• In these units, intensity of sunlight striking
  Venus is 193

Earth absorbs
units
Venus absorbs
units
Thus, Earth absorbs sunlight at a greater rate
than Venus does. Amazing, but true!
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Absorption of Solar Radiation Taking into Account
Distance to Sun and Albedo

• Let intensity of sunlight striking Earth be
  denoted by 100
• In these units, intensity of sunlight striking
  Venus is 193

Earth absorbs 100 x 0.70
70
units
Venus absorbs 193 x 0.30
58
units
Thus, Earth absorbs sunlight at a greater rate
than Venus does!
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Temperature Taking Into Account Distance to Sun
and Albedo

• If a planets mean surface temperature were
  determined solely by the rate of absorption of
  solar radiation,
• Venus would be ______ than Earth.

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Temperature Taking Into Account Distance to Sun
and Albedo

• If a planets mean surface temperature were
  determined solely by the rate of absorption of
  solar radiation,
• Venus would be colder than Earth.

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Actual Surface Temperatures

• Based on average measurements combining surface
  air temperature and sea surface temperatures
• Earths mean surface temperature is about ______
• Venus mean surface temperature is ______
• So
• Venus absorbs less sunlight than Earth, yet
• Venus surface is much hotter than Earths
• Why?

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Actual Surface Temperatures

• Based on average measurements combining surface
  air temperature and sea surface temperatures
• Earths mean surface temperature is about 15C
• Venus mean surface temperature is 480C!
• So
• Venus absorbs less sunlight than Earth, yet
• Venus surface is much hotter than Earths
• Why?

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Recap

• Rate of absorption of sunlight can be calculated
  from outer space distance to sun and albedo are
  all that are required
• Surface temperature is not correctly predicted
  from rate of absorption of sunlight
• What could cause such a difference?

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Recap

• Rate of absorption of sunlight can be calculated
  from outer space distance to sun and albedo are
  all that are required
• Surface temperature is not correctly predicted
  from rate of absorption of sunlight
• What could cause such a difference?
• The respective atmospheres of the Earth and Venus

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Atmospheres of Earth and Venus (Gases)

• Earth
• Nitrogen (N2)
• Oxygen (O2)
• Argon (Ar)
• Water Vapor (H2O)
• Carbon Dioxide (CO2)

• Venus
• Carbon Dioxide
• Nitrogen

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Principal Atmospheric Gases

• Earth

• Venus

Compare the amount of CO2
Unit 1018 g
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Comparison of Atmospheres

• Conclusions

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Comparison of Atmospheres

• Conclusions
• Venus has a much more massive atmosphere than
  Earth.
• Venus atmosphere is mostly CO2.
• The mass of CO2 in Venus atmosphere is almost
  100 times greater than the total mass of Earths
  atmosphere.

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Why is CO2 So Important?

• Carbon Dioxide is a greenhouse gas.
• Greenhouse gases are those gases that cause the
  greenhouse effect.
• The greenhouse effect makes a planets surface
  temperature warmer than it would otherwise be.
• The stronger the greenhouse effect, the warmer
  the surface (other factors being equal).

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Why is CO2 So Important?

• Carbon Dioxide is a greenhouse gas.
• Greenhouse gases are those gases that cause the
  greenhouse effect.
• The greenhouse effect makes a planets surface
  temperature warmer than it would otherwise be.
• The stronger the greenhouse effect, the warmer
  the surface (other factors being equal).
• Consider the blanket analogy

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Greenhouse Gases

• Water Vapor
• Carbon Dioxide
• Methane (CH4)
• Nitrous Oxide (N2O)
• Ozone (O3)
• CFCs (chlorofluorocarbons)

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Comparison of Greenhouse Effects

• Venus atmosphere contains 25, 000 times as
  much greenhouse gas as Earths!
• So, Venus has a much stronger greenhouse effect
  than Earth.
• Thus, Venus has a much hotter surface than Earth,
  despite the fact that Venus absorbs less sunlight
  than Earth.

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What does this have to do with climate?

• Greenhouse gases like CO2 play an important role
  in determining surface temperatures.
• Changes in greenhouse gases, thus can potentially
  increase or decrease surface temperatures.

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What does this have to do with climate?

• Greenhouse gases like CO2 play an important role
  in determining surface temperatures.
• Changes in greenhouse gases, thus can potentially
  increase or decrease surface temperatures.
• Therefore, the temperature of earth has more to
  do with the Earths atmosphere than how close the
  earth is to the sun.

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Activity 1 Greenhouse Effect