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Here comes the sun: Aerosols and Solar Dimming

Here comes the sun: Aerosols and Solar Dimming. Lelia Hawkins ESP Seminar November 17, 2006. An aerosol is . . . . . . a liquid or solid particle, suspended in a gas. Nitrates and Soot. Aerosol Sources. Dust. VOCs. Sea Salt. Ash and Sulfate. Sulfate. Black Carbon.

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Here comes the sun: Aerosols and Solar Dimming

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  1. Here comes the sun:Aerosols and Solar Dimming Lelia Hawkins ESP Seminar November 17, 2006

  2. An aerosol is . . . . . . a liquid or solid particle, suspended in a gas.

  3. Nitrates and Soot Aerosol Sources Dust VOCs Sea Salt Ash and Sulfate Sulfate Black Carbon

  4. Aerosols and Climate:the Direct Effects Sulfate aerosols Black carbon and soot

  5. Aerosols and Climate:the Indirect Effects Clouds are more reflective . . . And longer lasting . . .

  6. Increasing Aerosol Loading • Lower surface solar radiation • Cool surface Increasing GHGs • Warm surface Observations show 0.15°C warming per decade over the last 50 years

  7. Warmer world, decreased evaporation?? Expected Observed Pan evaporation paradox

  8. Observed reductions in evaporation Decreased pan evaporation by 97 mm per warm season between 1950-1995

  9. INDOEX:Indian Ocean Experiment Ramanathan et al. 2001

  10. INDOEX:Indian Ocean Experiment Continental Air (Polluted) Mixed Air Marine Air (Unpolluted) Ramanathan et al. 2001

  11. Surface Cooling • 20 Watts/m2 • average Compare 20 watts to Total ocean heat flux (40 Watts/m2) Ramanathan et al. 2001

  12. So the big conclusion is . . . Strong present-day aerosol cooling implies a hot future! Andreae et al., 2005 Why?

  13. Because of:The lifetime effect • CO2 lives about 100 years in our atmosphere. • Aerosols last days to weeks. And . . .

  14. Projected Emissions Future emissions of cooling aerosols from the IPCC-SRES A2. Andreae et al., 2005

  15. Climate Sensitivity-Response to a Perturbation Too low Too low Too high We need to better understand present day forcing to better predict future warming. Andreae et al., 2005

  16. “Deceitful” observed surface temp T = 1 K to 1.6 K T = 0.6 K

  17. What does the future hold? Projected temperature rise from IPCC-TAR Scenario A2 Andreae et al., 2005

  18. Conclusions • Aerosols may be responsible for the “missing” warming signal. • Climate sensitivity may currently under-predict warming due to doubling of CO2 • Aerosol pollution levels are changing, and are predicted to decrease world-wide.

  19. References

  20. References • http://www.scienceagogo.com/news/20020204005723data_trunc_sys.shtml • http://www.realclimate.org/index.php?p=110 • Peterson et al., 1995, Evaporation losing its strength, Nature (377)

  21. Thank you! Acknowledgements to Dr. Ramanathan for his assistance and guidance and to Google Images for the pictures.

  22. Global dimming or local dimming? < 0.1 million > 0.1 million -0.16 Wm-2yr-1 -0.41 Wm-2yr-1 Alpert et al., 2005

  23. The future looks “bright”! More effective clean air regulations Political transition in Eastern Europe Recently, recovery from Pinatubo Pre-1990 Increase = 8 Decrease = 24 Satellites show +0.16 Wm-2yr-1 Pinker et al., 2005 Post-1990 Increase = 26 Decrease = 6 Wild et al., 2005

  24. Deriving climate sensitivity 3.7 Wm-2 Andreae et al., 2005

  25. The warmest decade since 1861 IPCC-TAR

  26. Shallow Cloud Cooling 4% global increase = 2-3K of cooling Increase in Atlantic shallow clouds by 20% to 40% Aerosol reflected flux at TOA due to direct (1/3) and Twomey (2/3) effects Kaufman et al., 2005

  27. How does it work? TOA S/4*(1-albedo) =  Ta4 + (1-) Ts4 atmosphere S/4*(1-albedo)*(absorbed) = 2 Ta4 -  Ts4 S/4*(1-albedo)*(1-absorbed) +  Ta4 = Ts4 Surface

  28. What is solar dimming? • Direct: Scatter and absorb solar radiation. • Indirect: Longer lasting and more reflective clouds (Twomey Effect) • Net reduction in surface solar radiation

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