1 MET 112 Global Climate Change 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  Climate Change

2 MET 112 Global Climate Change 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

3 MET 112 Global Climate Change Unit Review  What was today’s 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?

Three temperature scales: KelvinKelvin CelsiusCelsius FahrenheitFahrenheit What does temperature mean physically?What does temperature mean physically? What does 0° K mean?What does 0° K mean?

Three temperature scales: KelvinKelvin CelsiusCelsius FahrenheitFahrenheit What does temperature mean physically?What does temperature mean physically? What does 0° K mean?What does 0° K mean? °K= °C+273

6 MET 112 Global Climate Change The Solar System  “The nine planets”The nine planets

7 MET 112 Global Climate Change Average Surface Temperature of Earth and Venus: Factors to consider      

8 MET 112 Global Climate Change 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?

9 MET 112 Global Climate Change Source of Energy: The Sun Sun radiates energy; Energy “radiates out” with distance

10 MET 112 Global Climate Change Earth and Venus Venus Earth Based on solely the position of Venus and the Earth, which planet would be warmer?

11 MET 112 Global Climate Change 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?

12 MET 112 Global Climate Change 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 …

13 MET 112 Global Climate Change 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 …

14 MET 112 Global Climate Change  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

15 MET 112 Global Climate Change  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

16 MET 112 Global Climate Change Albedo  Albedo: The fraction of light reflected by an object or a surface  White objects have ___________  Black objects have ___________

17 MET 112 Global Climate Change 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

18 MET 112 Global Climate Change 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

19 MET 112 Global Climate Change 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

20 MET 112 Global Climate Change 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.

21 MET 112 Global Climate Change 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.

22 MET 112 Global Climate Change 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!

23 MET 112 Global Climate Change 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!

24 MET 112 Global Climate Change 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.

25 MET 112 Global Climate Change 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.

26 MET 112 Global Climate Change 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?

27 MET 112 Global Climate Change 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?

28 MET 112 Global Climate Change 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? 

29 MET 112 Global Climate Change 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

30 MET 112 Global Climate Change Atmospheres of Earth and Venus (Gases)  Earth  Venus 1. 2.

31 MET 112 Global Climate Change 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

32 MET 112 Global Climate Change Principal Atmospheric Gases Earth Venus GASMASS Nitrogen 3870 (75%) Oxygen 1185 (23%) 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

33 MET 112 Global Climate Change Comparison of Atmospheres Conclusions:

34 MET 112 Global Climate Change Comparison of Atmospheres Conclusions: 1.Venus has a much more massive atmosphere than Earth. 2.Venus’ atmosphere is mostly CO 2. 3.The mass of CO 2 in Venus’ atmosphere is almost 100 times greater than the total mass of Earth’s atmosphere.

35 MET 112 Global Climate Change 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). 

36 MET 112 Global Climate Change 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

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39 MET 112 Global Climate Change Greenhouse Gases      

40 MET 112 Global Climate Change Greenhouse Gases  Water Vapor  Carbon Dioxide  Methane (CH 4 )  Nitrous Oxide (N 2 O)  Ozone (O 3 )  CFC’s (chlorofluorocarbons)

41 MET 112 Global Climate Change 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.

42 MET 112 Global Climate Change What does this have to do with climate?   Changes in greenhouse gases, thus can potentially increase or decrease surface temperatures. 

43 MET 112 Global Climate Change 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.

44 MET 112 Global Climate Change Activity 1b Answer each question and turn in at the beginning of the next class 1.If the earth’s albedo was to increase due to more clouds, how would the Earth’s temperature change? 2.Today, greenhouse gases like CO 2 are increasing in the atmosphere. How would that would change the earth’s temperature? 3.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).