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Units MET 112 Global Climate Change - Lecture 2 “Greenhouse Effect: Earth and Venus” Our class will use both English and Metric unit systems. Most important: – Distance (kilometres and miles) – Temperature (ºC and ºF) Dr. Eugene Cordero San Jose State University, Spring 2004 Outline Earth and Venus Greenhouse effect Climate Change MET 112 Global Climate Change 1 Conversions: 1.6 km = 1 mile; 1 km = 0.61 miles (9/5 x ºC) + 32 = ºF (ºF – 32) x 5/9 = ºC MET 112 Global Climate Change Unit Review Three temperature scales: •Kelvin •Celsius •Fahrenheit What was today’s low temperature in ºC? •What does temperature mean physically? 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? MET 112 Global Climate Change •What does 0° K mean? 3 Average Surface Temperature of Earth and Venus: Factors to consider Source of Energy: The Sun Which planet is closer to the Sun? Which planet is more reflective? Which planet has a larger ability to absorb and retain solar energy? MET 112 Global Climate Change 2 Sun radiates energy; Energy “radiates out” with distance 7 MET 112 Global Climate Change 8 Temperature Based Only on Distance to the Sun Earth and Venus Venus Based on solely the position of Venus and the Earth, which planet would be warmer? Based only on distance to the sun, – Average surface temperatures would be as follows if the planets absorbed all of the incoming sunlight: – – However … Earth MET 112 Global Climate Change 9 Albedo MET 112 Global Climate Change 11 Albedo Albedo: The fraction of light reflected by an object or a surface White objects have ___________ Black objects have ___________ 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 … MET 112 Global Climate Change 13 Comparison of Earth and Venus MET 112 Global Climate Change 15 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. Venus Let’s re-examine the surface temperatures with this information. Earth Venus is completely covered by highly reflective clouds; Earth is partially covered by clouds. Which planet has a higher albedo? _______________ MET 112 Global Climate Change 17 MET 112 Global Climate Change 19 Absorption of Solar Radiation Taking into Account Distance to Sun and Albedo Temperature 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 If a planet’s mean surface temperature were determined solely by the rate of absorption of solar radiation, – Venus would be ______ than Earth. Thus, Earth absorbs sunlight at a greater rate than Venus does. Amazing, but true! MET 112 Global Climate Change 21 Actual Surface Temperatures Recap Based on average measurements combining surface air temperature and sea surface temperatures: – Earth’s mean surface temperature is about ______ – Venus’ mean surface temperature is ______ 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? So… Venus absorbs less sunlight than Earth, yet Venus’ surface is much hotter than Earth’s Why? MET 112 Global Climate Change 25 Earth 1. 2. 3. 4. 5. Nitrogen (N2) Oxygen (O2) Argon (Ar) Water Vapor (H2O) Carbon Dioxide (CO2) 27 MET 112 Global Climate Change Atmospheres of Earth and Venus (Gases) 23 MET 112 Global Climate Change Principal Atmospheric Gases Venus Earth Venus 1. Carbon Dioxide 2. Nitrogen GAS MASS Nitrogen 3870 (75%) Oxygen 1185 (23%) Argon 67 (1%) Water Vapor 17 (0.3%) CO2 3 (0.06%) TOTAL 5140 GAS MASS CO2 ~500, 000 (96%) N2 ~20, 000 TOTAL 520, 000 (4%) Compare the amount of CO2 Unit: 1018 g MET 112 Global Climate Change 29 MET 112 Global Climate Change 30 Comparison of Atmospheres Why is CO2 So Important? Conclusions: 1. 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). 2. 3. MET 112 Global Climate Change 31 Greenhouse Gases MET 112 Global Climate Change 33 Comparison of Greenhouse Effects Water Vapor 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. Carbon Dioxide Methane (CH4) Nitrous Oxide (N2O) Ozone (O3) CFC’s (chlorofluorocarbons) MET 112 Global Climate Change 37 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 Earth’s atmosphere than how close the earth is to the sun. MET 112 Global Climate Change 39 MET 112 Global Climate Change 38