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1 MET 12 Global Climate Change – Lecture 3 “Greenhouse Effect: Earth and Venus” Shaun Tanner San Jose State University  By the end of this chapter you.

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Presentation on theme: "1 MET 12 Global Climate Change – Lecture 3 “Greenhouse Effect: Earth and Venus” Shaun Tanner San Jose State University  By the end of this chapter you."— Presentation transcript:

1 1 MET 12 Global Climate Change – Lecture 3 “Greenhouse Effect: Earth and Venus” Shaun Tanner San Jose State University  By the end of this chapter you should: Understand the differences in the atmospheres of Venus and Earth Understand the differences in the atmospheres of Venus and Earth Know how a changing albedo can change climate Know how a changing albedo can change climate Understand the role of greenhouses gases and the runaway greenhouse effect Understand the role of greenhouses gases and the runaway greenhouse effect

2 2 The Solar System  “The nine planets”The nine planets

3 3 The Solar System  “The nine planets”The nine planets

4 4 Average Surface Temperature of Earth and Venus: Factors to consider      

5 5  Which planet is closer to the Sun?  Which planet is more reflective?  Which planet has a larger ability to absorb and retain solar energy?

6 6 Source of Energy: The Sun Sun radiates energy; Energy “radiates out” with distance

7 7 Earth and Venus Venus Earth Based on solely the position of Venus and the Earth, which planet would be warmer?

8 8 Earth and Venus Venus Earth Sunlight striking Venus is 93% stronger than sunlight striking Earth, thus we would expect Venus to be warmer Based on solely the position of Venus and the Earth, which planet would be warmer?

9 9 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: 5°C –Venus: 55°C  However …

10 10  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 … Albedo

11 11  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

12 12 Albedo  Albedo: The fraction of light reflected by an object or a surface  White objects have ___________  Black objects have ___________

13 13 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

14 14 Comparison of Earth and Venus Venus is completely covered by highly reflective clouds; Earth is partially covered by clouds. Which planet has a higher albedo? _______________ Venus Earth

15 15 Comparison of Earth and Venus Venus is completely covered by highly reflective clouds; Earth is partially covered by clouds. Which planet has a higher albedo? _______________ Venus Earth Venus

16 16 Comparison of Earth and Venus  Earth’s albedo is ____  Venus’ albedo is ____ Earth absorbs__% of the sunlight that strikes it. Venus absorbs__% of the sunlight that strikes it. Let’s re-examine the surface temperatures with this information.

17 17 Comparison of Earth and Venus  Earth’s albedo is 30%  Venus’ albedo is 70% Earth absorbs70% of the sunlight that strikes it. Venus absorbs30% of the sunlight that strikes it. Let’s re-examine the surface temperatures with this information.

18 18 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 absorbsunits Venus absorbsunits Thus, Earth absorbs sunlight at a greater rate than Venus does. Amazing, but true!

19 19 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 absorbs100 x 0.70 = 70units Venus absorbs193 x 0.30 =58units Thus, Earth absorbs sunlight at a greater rate than Venus does!

20 20 Temperature Taking Into Account Distance to Sun and Albedo  If a planet’s mean surface temperature were determined solely by the rate of absorption of solar radiation, –Venus would be ______ than Earth.

21 21 Temperature Taking Into Account Distance to Sun and Albedo  If a planet’s mean surface temperature were determined solely by the rate of absorption of solar radiation, –Venus would be colder than Earth.

22 22 Actual Surface Temperatures  Based on average measurements combining surface air temperature and sea surface temperatures: –Earth’s mean surface temperature is about ______ –Venus’ mean surface temperature is ______  So…  Venus absorbs less sunlight than Earth, yet  Venus’ surface is much hotter than Earth’s  Why?

23 23 Actual Surface Temperatures  Based on average measurements combining surface air temperature and sea surface temperatures: –Earth’s mean surface temperature is about 15°C –Venus’ mean surface temperature is 480°C!  So…  Venus absorbs less sunlight than Earth, yet  Venus’ surface is much hotter than Earth’s  Why?

24 24 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? 

25 25 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

26 26 Atmospheres of Earth and Venus (Gases)  Earth  Venus 1. 2.

27 27 Atmospheres of Earth and Venus (Gases)  Earth 1.Nitrogen (N 2 ) 2.Oxygen (O 2 ) 3.Argon (Ar) 4.Water Vapor (H 2 O) 5.Carbon Dioxide (CO 2 )  Venus 1.Carbon Dioxide 2.Nitrogen

28 28 Principal Atmospheric Gases Earth Venus GASMASS Nitrogen 3870 (78%) Oxygen 1185 (21%) Argon 67 (<1%) Water Vapor 17 (0.3%) CO 2 3 (0.06%) TOTAL 5140 GASMASS CO 2 ~500, 000 (96%) N2N2 ~20, 000 (4%) TOTAL520, 000 Unit: g Compare the amount of CO 2

29 29 Comparison of Atmospheres Conclusions:  Venus has a much more massive atmosphere than Earth.  Venus’ atmosphere is mostly CO 2.  The mass of CO 2 in Venus’ atmosphere is almost 100 times greater than the total mass of Earth’s atmosphere.

30 30 Why is CO 2 So Important?  Carbon Dioxide is a greenhouse gas.  Greenhouse gases are those gases that cause the greenhouse effect.  The greenhouse effect makes a planet’s 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

31

32 32 Greenhouse Gases  Water Vapor  Carbon Dioxide  Methane (CH 4 )  Nitrous Oxide (N 2 O)  Ozone (O 3 )  CFC’s (chlorofluorocarbons)

33 33 Comparison of Greenhouse Effects  Venus’ atmosphere contains ~ 25, 000 times as much greenhouse gas as Earth’s!  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.

34 34 What does this have to do with climate?  Greenhouse gases like CO 2 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 Earth’s atmosphere than how close the Earth is to the sun.

35 35 Activity 1b Answer each question and turn in at the beginning of the next class  If the Earth’s albedo was to increase due to more clouds, how would the Earth’s temperature change?  Today, greenhouse gases like CO 2 are increasing in the atmosphere. How would that would change the Earth’s temperature?  If increases in greenhouse gases act to produce more clouds, how would that change the Earth’s temperature (consider your answers to 1 and 2).


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