1. 1 MET 112 Global Climate Change MET 112 Global Climate Change - Lecture 4 Clouds and Global Climate Dr. Craig Clements San Jose State University

2. In class assignment #2 How does this situation affect the climate? (2-3 sentences)

3. 3 MET 112 Global Climate Change 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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6. 6 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

7. Water freely evaporating and condensing Since more water molecules are evaporating than condensing, then net evaporation is occurring.

8. 8 MET 112 Global Climate Change Lid on: Now, evaporation and condensation are equal. The air above water is now called ‘saturated’. The humidity is now 100%

9. 9 MET 112 Global Climate Change 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  Condensation occurs primarily as temperature cools: -colder the molecules more likely they are to ‘stick’ to other molecules

10. 10 MET 112 Global Climate Change http://www.ssec.wisc.edu/data/comp/cmoll/cmoll.html

11. 11 MET 112 Global Climate Change 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.

12. 12 MET 112 Global Climate Change 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?

13. 13 MET 112 Global Climate Change Which day would be warmer? 1.First day (clear) 2.Second day (cloudy) 3.Both the same

14. 14 MET 112 Global Climate Change Which evening would be warmer? 1.First day (clear) 2.Second day (cloudy) 3.Both the same

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16. 16 MET 112 Global Climate Change 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?

17. Clouds and climate Cloud A: Low level, (dark, thick) Cloud B: High level, light (sub visible or thin) (sub 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

18. 18 MET 112 Global Climate Change Changes in clouds  Increases in low level clouds will: –  Increases in high level clouds will:

19. 19 MET 112 Global Climate Change 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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29. Explain how the earth’s climate would change as a result of aircarft contrails.

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33. 33 MET 112 Global Climate Change 1.What percentage of the sun’s radiation is a)absorbed by the Earth’s surface? b)absorbed by the atmosphere c)reflected out to space? 2.What percentage of the energy received by the earth’s surface comes directly from greenhouse gas emissions? 3.If the sun’s radiation was to increase by 10%, how would the following energy units change (increase, decrease or stay the same) a)Energy gained by the Earth’s surface. b)Energy lost by the Earth’s surface. c)Energy emitted by greenhouse gases. d)Energy lost to space. Questions