1. The Atlantic Multidecadal Oscillation, Climate Change, and Atlantic Hurricanes Michael E. Mann Department of Meteorology/Earth and Environmental Systems Institute/Department of Geosciences Pennsylvania State University Dept. of Geography Coffee Hour September 25, 2006

2. Katrina (Aug 28 ’05) Climate Change Influence on the Destructive Potential of Atlantic Hurricanes?

3. Climate Model Predictions Knutson, T. K., and R. E. Tuleya, 2004: Impact of CO2-induced warming on simulated hurricane intensity and precipitation: Sensitivity to the choice of climate model and convective parameterization. Journal of Climate, 17(18), 3477-3495.

4. Observed Trends P. J. Webster, G. J. Holland, J. A. Curry, H.-R. Chang Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment, Science, 309, Issue 5742, 1844-1846, 2005.

5. Emanuel, K. (2005), Increasing destructiveness of tropical cyclones over the past 30 years, Nature, online publication; published online 31 July 2005 | doi: 10.1038/nature03906 Observed Trends

6. Emanuel, K. (2005), Increasing destructiveness of tropical cyclones over the past 30 years, Nature, online publication; published online 31 July 2005 | doi: 10.1038/nature03906 Climate Change?natural variability?OR

7. EL NINO/SOUTHERN OSCILLATION (“ENSO”) Multivariate ENSO Index (“MEI”)

8. Secular Warming Pattern Mann, M.E., Park, J., Oscillatory Spatiotemporal Signal Detection in Climate Studies: A Multiple-Taper Spectral Domain Approach, Advances in Geophysics, 41, 1-131, 1999.

9. Multidecadal Pattern Cold seasonWarm season

10. Mann, M.E., Park, J., Bradley, R.S., Global Interdecadal and Century-Scale Climate Oscillations During the Past Five Centuries, Nature, 378, 266-270, 1995. Multidecadal Pattern

11. “Atlantic Multidecadal Oscillation” (AMO) Model

14. Influence of AMO and Hurricanes? Mann, M.E., Emanuel, K.A., Atlantic Hurricane Trends linked to Climate Change, Eos, 87, 24, p 233, 238, 241, 2006.

15. Global Mean Aug-Oct SST [G(t)] (Aug-Oct) T(t) =  G(t) trop Atl (6-18N, 20-60W) Aug-Oct SST Mann, M.E., Emanuel, K.A., Atlantic Hurricane Trends linked to Climate Change, Eos, 87, 24, p 233, 238, 241, 2006. Influences on tropical Atlantic SST

16. Residual [R(t)] Estimation of AMO Influence Mann, M.E., Emanuel, K.A., Atlantic Hurricane Trends linked to Climate Change, Eos, 87, 24, p 233, 238, 241, 2006.

17. Spectrum of Residual (1870-1999) Mann, M.E., Emanuel, K.A., Atlantic Hurricane Trends linked to Climate Change, Eos, 87, 24, p 233, 238, 241, 2006. Estimation of AMO Influence

18. Spectrum of Residual (1870-1949) Mann, M.E., Emanuel, K.A., Atlantic Hurricane Trends linked to Climate Change, Eos, 87, 24, p 233, 238, 241, 2006. Estimation of AMO Influence

19. Residual [R(t)] Mann, M.E., Emanuel, K.A., Atlantic Hurricane Trends linked to Climate Change, Eos, 87, 24, p 233, 238, 241, 2006. Estimation of AMO Influence

20. Hansen, J. et al, Efficacy of climate forcings. J. Geophys. Res. 110, D18104, doi:10.1029/2005JD005776 (2005).)

21. T(t) =  G(t)+  S(t) trop Atl (6-18N, 20-60W) Aug-Oct SST  S(t)  G(t) Influences on tropical Atlantic SST Mann, M.E., Emanuel, K.A., Atlantic Hurricane Trends linked to Climate Change, Eos, 87, 24, p 233, 238, 241, 2006.

22. trop Atl (6-18N, 20-60W) Aug-Oct SST T(t) =  G(t)+  S(t) (full data) Influences on tropical Atlantic SST Mann, M.E., Emanuel, K.A., Atlantic Hurricane Trends linked to Climate Change, Eos, 87, 24, p 233, 238, 241, 2006.

23. T(t) =  G(t)+  S(t) (full data) trop Atl (6-18N, 20-60W) Aug-Oct SST T(t) =  G(t)+  S(t) (fit to 1870-1969) T(t) =  G(t)+  S(t) (predicted 1970-1999) Mann, M.E., Emanuel, K.A., Atlantic Hurricane Trends linked to Climate Change, Eos, 87, 24, p 233, 238, 241, 2006. Influences on tropical Atlantic SST

24. Residual [R(t)] Mann, M.E., Emanuel, K.A., Atlantic Hurricane Trends linked to Climate Change, Eos, 87, 24, p 233, 238, 241, 2006. Estimation of AMO Influence

25. Spectrum of Residual (1870-1999) “Before” Mann, M.E., Emanuel, K.A., Atlantic Hurricane Trends linked to Climate Change, Eos, 87, 24, p 233, 238, 241, 2006. Estimation of AMO Influence

26. Spectrum of Residual (1870-1999) “After” Mann, M.E., Emanuel, K.A., Atlantic Hurricane Trends linked to Climate Change, Eos, 87, 24, p 233, 238, 241, 2006. Estimation of AMO Influence

27. TC #s vs T(t) TC #s vs R(t) AMO Influence on TCs?

28. CONCLUSIONS AMO does not significantly project onto tropical North Atlantic SST Apparent multidecadal oscillation in tropical Aug-Oct Atlantic SST an artifact of late 20 th century aerosol forcing Anthropogenic climate change (including tropospheric aerosol trends) appears primary factor influencing tropical Aug-Oct Atlantic SST and North Atlantic Tropical Cyclones (TCs) Late 20th century tropospheric aerosol cooling has offset a substantial amount of anthropogenic greenhouse gas warming in the region and has thus likely suppressed even greater potential increases in TC activity.

29. “Atlantic Multidecadal Oscillation” (AMO) Observations

30. Model Observations

31. “Pacific Decadal Oscillation” (PDO)