1. 1 MET 12 Global Climate Change - Lecture 4 Clouds and global climate Shaun Tanner San Jose State University  By the end of this chapter you should: Understand the role of water in the Earth system Understand the role of water in the Earth system Know the roles of clouds Know the roles of clouds Understand how high clouds differ from low clouds in terms of albedo and absorption Understand how high clouds differ from low clouds in terms of albedo and absorption

2. 2 Questions  What role do clouds play on the Earth’s climate?  What would happen to our climate if clouds were to increase/decrease?

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5. 5 Water in the atmosphere  Definitions: –Evaporation: –Condensation: –Precipitation: Process where a liquid changes into a gas Any liquid or solid water that falls from the atmosphere to the ground. (i.e. RAIN!) Process where a gas changes into a liquid

6. 6 Condensation  The process by which water vapor changes to a cloud droplet  Water vapor molecules may ‘stick’ to condensation nuclei and grow (billions) to eventually form cloud droplet.  Examples of condensation nuclei include: a. a. b. b. c. c.

7. 7 Condensation  The process by which water vapor changes to a cloud droplet  Water vapor molecules may ‘stick’ to condensation nuclei and grow (billions) to eventually form cloud droplet.  Examples of condensation nuclei include: a. Dust b. Salt c. Smoke

8. 8 Clouds and radiation Cloud - Climate Interactions Albedo effect - COOLING  Clouds reflect incoming solar radiation.  The cloud droplet size and total water content determine the overall reflectivity. Greenhouse effect - WARMING  Clouds are good absorbers (and emitters) of long wave (infrared) radiation.

9. 9 Clouds and day to day temperatures Imagine that you are going camping in the Sierras with your friends. On the first day (and evening) it is cloudy, while on the second day (and evening) it is clear. Based on this information alone: Which day would be warmer? Which evening would be warmer? Explain your answers.

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11. 11 Low and High clouds Consider two types of clouds: 1.Low levels clouds 2.High levels clouds Q: How is the Earth’s surface energy budget different for low clouds compared to high clouds?

12. 12 Clouds and climate Cloud A: Low level, (dark, thick) Cloud B: High level, light (sun visible or thin) (sun visible or thin) Excellent reflector of incoming radiation; good absorber/emitter of infrared radiation Fair/poor reflector of incoming radiation; good/excellent absorber/emitter of infrared radiation  So, clouds both warm and cool the earth.  Overall, though, clouds act to cool the earth

13. 13 Changes in clouds  Increases in low level clouds will: –  Increases in high level clouds will:

14. 14 Changes in clouds  Increases in low level clouds will: –cool the surface (cooling outweighs warming)  Increases in high level clouds will: –warm the surface (warming outweighs cooling)

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21. How would the earth’s climate change as a result of aircraft contrails. 21

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23. 23 Definitions  Insolation –  Solstice –  Equinox –

24. 24 Definitions  Insolation –  Solstice –  Equinox – Incoming solar radiation day of the year when the sun shines directly over 23.5°S or 23.5°N days of the year when the sun shines directly over the equator

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27. 27 What influences incoming solar energy?  The Sun’s angle of incidence: –Lower sun angle, –Higher sun angle,  Length of time the Sun shines each day: –Summer season, –Winter season, more incoming energy less incoming energy less sun hours more sun hours

28. 28 What month do you think this graph represents? a) December b) March c) June d) September

29. 29 What month do you think this graph represents? a) December b) March c) June d) September Answer: December

30. 30 Review questions  On June 21 st, at what latitude is the sun directly overhead at noon?  On September 22 nd, at what latitude is the sun directly overhead at noon?  How many hours of daylight are present at the South Pole on February 20 th ?  Where would you expect to have longer days; 45 ° N on June 21 st or 50°S on Dec 21 st ?

31. 31 Review questions  On June 21 st, at what latitude is the sun directly overhead at noon?  On September 22 nd, at what latitude is the sun directly overhead at noon?  How many hours of daylight are present at the South Pole on February 20 th ?  Where would you expect to have longer days; 45 ° N on June 21 st or 50°S on Dec 21 st ? 23.5 ° North (tropic of cancer) 0° (equator) 24 50 °S