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90. 60. Mean annual temperature (°F). 30. 0. 160. 0. 80. 120. 40. Mean annual precipitation (inches). Evaporation. To change phase, H2O molecules need energy to break bonds and escape from the liquid. Hotter means more water vapor in atmosphere.

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  1. 90 60 Mean annual temperature (°F) 30 0 160 0 80 120 40 Mean annual precipitation (inches)

  2. Evaporation To change phase, H2O molecules need energy to break bonds and escape from the liquid

  3. Hotter means more water vapor in atmosphere

  4. evaporation rates dependent not only on temperature but also wind speed

  5. Condensation

  6. Most condensation falls as rain

  7. Clouds need cloud condensation nuclei (CCNs)

  8. Aerosol Cycles cloud Cloud uptake Evaporation Precursor gases: Nucleation (sulfur dioxide, nitrogen oxides) Growth Rainout Dry deposition Automobiles Biomass burning Industry [adapted from Jakob, 1999]

  9. Aerosols and Climate: Direct Effect Direct Effect: Scattering and absorption by particles photo: SeaWifs website

  10. Aerosol indirect effect [Durkee et al., 2000]

  11. Aerosol Indirect Effect Anthropogenic aerosol example using ship emissions: (Johnson et al., 1996)

  12. Cloud Formation in a Clean and Polluted Atmosphere

  13. This cloud has only few cloud droplets, hence, reflects less sunlight (darker cloud). This cloud has more cloud droplets, hence, reflects more sunlight (lighter cloud).

  14. Low Clouds Very thick water clouds reflect large amounts of sunlight Very near the surface, temperature of the cloud effectively the same as surface. Infrared radiation is therefore about the same - almost like the cloud wasn’t there! NET EFFECT: Cooling

  15. High Clouds Thin, cold ice clouds reflect less sunlight Extremely cold, emits infrared at colder temperatures, prevents warmer surface infrared from escaping to space NET EFFECT: Warming

  16. Surface temperature changes from 1750 to 1990 Greenhouse gases only Aerosols only Greenhouse gases and aerosols Global and annual mean changes: Greenhouse gases only: 1.7 °C Aerosols only: -0.9 °C Greenhouse gases and aerosols: 0.6 °C Observed temperature increase over the last 140 years: 0.6 °C

  17. Surface temperature changes from 1750 to 1990 Aerosols only (°C)

  18. Hydrological Cycle Cloud Albedo Cloud Formation CCN formation volatile organic carbon molecules Precipitation/ Water Stress Surface Temperature

  19. We know how trees respond to elevated CO2 There is a wealth of data from many CO2 enrichment studies demonstrating physiological responses of seedlings and young trees • Elevated CO2 stimulates photosynthesis • Trees grow faster in elevated CO2 and are bigger at the end of the experiment • N concentrations are reduced • No large changes in structure • Stomatal conductance often is lower

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