Wednesday, Nov. 26
Syllabus, class notes, and homeworks are at:
www.as.utexas.edu courses AST 301, Lacy
Reading for this week: chapter 17
We won’t have a help session this week.
Today: the greenhouse effect
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Prepare for your exams
Study with the several resources on Docsity
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Earn points by helping other students or get them with a premium plan
Astrobiology 101: Understanding the Greenhouse Effect and Planetary Temperatures, Study notes of Astronomy
Class notes and quiz materials for a university-level astrobiology course, focusing on the greenhouse effect and its impact on planetary temperatures. Students will learn about thermal equilibrium, the role of atmospheric gases, and the consequences of human activities on earth's climate. Examples of planetary temperatures and quiz questions.
Typology: Study notes
Pre 2010
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Wednesday, Nov. 26
Syllabus, class notes, and homeworks are at: www.as.utexas.edu courses AST 301, Lacy Reading for this week: chapter 17 We won’t have a help session this week. Today: the greenhouse effect
Topics for this week
How can we use the concept of thermal equilibrium to calculate the temperature of the surface of a rock orbiting the Sun? How does the result depend on the distance of the rock from the Sun? How does the Earth’s atmosphere affect the surface temperature of the Earth? Why do Venus and Mars have such different surface temperatures? How are we changing the Earth’s atmosphere, and how do we think this will affect the surface temperature?
ABCD Quiz
The cooling of the surface of the Earth is dominated by: A. emission of infrared radiation B. reflection of sunlight by the surface C. evaporation of water D. conduction of heat into the air (During the day, heat is conducted into the air, but at night the heat flows from the air into the ground.)
ABCD Quiz
The greenhouse effect causes an increase in the temperature of the surface of the Earth by: A. preventing the radiation of infrared radiation by the ground B. preventing the infrared radiation from the ground from getting out to space C. preventing convection from removing heat from the ground D. heating the atmosphere so it can emit infrared radiation which adds to the heating of the ground I would accept answer B on a test, although D is better. C is important in real greenhouses.
Include only sunlight absorbed
Only the sunlight absorbed (not reflected) by the planet contributes to its heating. Recalculating the temperatures including only the absorbed sunlight we get lower temperatures: Planet black rock recalculated actual surface T Mercury 450 K 440 K 100-700 K Venus 330 K 230 K 700 K Earth 280 K 250 K 290 K Mars 227 K 217 K 220 K Jupiter 123 K 103 K 130 K
The greenhouse effect
By blocking some of the outgoing infrared radiation and returning it to the Earth, molecules in the Earth’s atmosphere force the temperature of the surface of the Earth to rise until the outgoing flow of energy matches the incoming flow. This is the greenhouse effect. Because of the greenhouse effect, the surface of the Earth is warm enough for us to live here. Only about on half of the radiation emitted by the surface of the Earth escapes to carry heat away from the Earth. As a result, the average temperature of the surface of the Earth is warm enough for life.
Differences between our atmospheres
Why do Venus, Earth, and Mars have such different atmospheres? Our atmosphere probably once was rich in CO 2 , but when CO 2 is dissolved in water it can react with metal ions to form limestone. Plankton and shellfish make this happen faster. Also, plants make cellulose from CO 2
releasing O 2
Venus has always been too hot for water to be liquid, so it had no way to remove the CO 2 from its atmosphere. So it has a very strong greenhouse effect. Mars probably once had oceans or lakes where limestone could form. It is also cold enough at its poles for CO 2 to freeze. And almost all of its water is frozen. So it has a very weak greenhouse effect.
Climate Change
If you’ve heard about the greenhouse effect, you’ve probably heard about how it is changing our climate. Although the greenhouse effect is desirable, and maybe necessary for life to exist on Earth, most life forms are slow to adapt to changes in the temperature. A rapid change in the greenhouse effect can be harmful. What are we doing that changes the greenhouse effect?
Will the temperature rise?
The direct effect of the CO 2 and other gasses we are putting into the atmosphere on the temperature of the surface of the Earth is relatively small. If nothing else changed the temperature would rise less than 1 o C in the next century. But other things will change. An increase in the temperature of the oceans will cause increased evaporation, increasing the amount of water vapor in the atmosphere. This will magnify the effect. But it will also get cloudier. This will decrease the heating.