1. MET 112 Global Climate Change - Lecture 5 Clouds and Global Climate Dr. Craig Clements San Jose State University

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

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

7. Lid on: Now, evaporation and condensation are equal. The air above water is now called ‘saturated’. The humidity is now 100%

8. 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

9. 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.

10. 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.

11. Which day would be warmer? 1.First day (clear) 2.Second day (cloudy) 3.Both the same

12. Which evening would be warmer? 1.First day (clear) 2.Second day (cloudy) 3.Both the same

14. 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?

15. 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

16. Cirrus clouds

17. Cirrocumulus clouds

18. Altocumulus clouds

19. Stratocumulus clouds

20. Cumulus clouds. Small cumulus clouds such as these are sometimes called fair weather cumulus, or cumulus humilis

21. stratus clouds

22. Explain how the earth’s climate would change as a result of aircraft contrails.

24. 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)

25. Controls on Climate  Seasonal temperature and precipitation patterns are generally attributable to:  Latitude  Mountains and highlands  Land and water location  Prevailing winds  Pressure and wind systems  Ocean currents

26. Questions  Indicate the warmest and coldest areas of the Earth.  Consider the temperature at 60N latitude. Indicate on the map the coldest and warmest places at 60N.  What is the temperature difference between these locations  What factors might explain this temperature difference?  Why is there not a similar difference seen at 60S?

27. Annual Surface Temperature

28. Climate controls: Latitude/Mountains  Latitude – Higher latitude climates are generally (cooler/warmer) – Lower latitudes climates are generally (cooler/warmer)  Mountains – Higher altitudes climate are generally (cooler/warmer): cooler temperatures – Windward side of mountains are generally (cooler/warmer) and (wetter/drier), than leeward side

29. Climate controls: Latitude/Mountains  Latitude – Higher latitude climates are generally (cooler/warmer) – Lower latitudes climates are generally (cooler/warmer)  Mountains – Higher altitudes climate are generally (cooler/warmer): cooler temperatures – Windward side of mountains are generally (cooler/warmer) and (wetter/drier), than leeward side

30. Controls on Climate  Seasonal temperature and precipitation patters are generally attributable to:  Latitude  Mountains and highlands  Land and water location  Prevailing winds  Pressure and wind systems  Ocean currents

32. Controls on Climate: Oceans  Ocean Temperatures –Coasts of continents are affected by ocean temperatures: Generally less temperature extremes compared to interior of continents –Cold oceans: –Warm oceans: generally produce cooler/drier conditions generally produce more warm/humid conditions

34. Cold ocean Warm ocean

36. Dry Humid

37. Controls on Climate: Pressure systems  Rising and sinking motion associated with low and high pressure affects climate  Areas where pressure seasonally low, –  Areas where pressure seasonally high, – Tropics: rainy Subtropical high (30N/30S): warm and dry

38. January Average sea-level Pressure and surface wind pattern

39. July Average sea-level Pressure and surface wind pattern