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

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

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

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

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

6. Increasing Aerosol Loading Lower surface solar radiation Cool surface 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?? ExpectedObserved 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 Ramanathan et al. 2001 Continental Air (Polluted) Marine Air (Unpolluted) Mixed Air

11. Surface Cooling -20 Watts/m 2 average Ramanathan et al. 2001 Compare 20 watts to Total ocean heat flux (40 Watts/m 2 )

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 CO 2 lives about 100 years in our atmosphere. Aerosols last days to weeks. CO 2 lives about 100 years in our atmosphere. Aerosols last days to weeks. And...

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

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

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

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

18. Conclusions Aerosols may be responsible for the “missing” warming signal. Climate sensitivity may currently under- predict warming due to doubling of CO 2 Aerosol pollution levels are changing, and are predicted to decrease world- wide. Aerosols may be responsible for the “missing” warming signal. Climate sensitivity may currently under- predict warming due to doubling of CO 2 Aerosol pollution levels are changing, and are predicted to decrease world- wide.

19. References

20. http://www.scienceagogo.com/news/20020204005723data_trunc_sys.s htmlhttp://www.scienceagogo.com/news/20020204005723data_trunc_sys.s html http://www.realclimate.org/index.php?p=110 Peterson et al., 1995, Evaporation losing its strength, Nature (377) http://www.scienceagogo.com/news/20020204005723data_trunc_sys.s htmlhttp://www.scienceagogo.com/news/20020204005723data_trunc_sys.s html 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. Acknowledgements to Dr. Ramanathan for his assistance and guidance and to Google Images for the pictures.

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

23. Wild et al., 2005 The future looks “bright”! Satellites show +0.16 Wm -2 yr -1 Pinker et al., 2005 Post-1990 Increase = 26 Decrease = 6 Pre-1990 Increase = 8 Decrease = 24 1.More effective clean air regulations 2.Political transition in Eastern Europe 3.Recently, recovery from Pinatubo

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

25. The warmest decade since 1861 IPCC-TAR

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

27. How does it work? atmosphere S/4*(1-albedo)*(absorbed) S/4*(1-albedo) Surface S/4*(1-albedo)*(1-absorbed) Ts4Ts4  Ts4 Ts4 (1-  )  T s 4  Ta4 Ta4  Ta4 Ta4 + + 2 Ta42 Ta4 - = = = TOA

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 Direct: Scatter and absorb solar radiation. Indirect: Longer lasting and more reflective clouds (Twomey Effect) Net reduction in surface solar radiation