The Atlantic Multidecadal Oscillation, Climate Change,

and Atlantic HurricanesMichael E. Mann

Department of Meteorology/Earth and Environmental Systems Institute/Department of Geosciences

Pennsylvania State University

Dept. of Geography Coffee HourSeptember 25, 2006

Katrina (Aug 28 ’05)

Climate Change Influence on the

Destructive Potential of

Atlantic Hurricanes?

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.

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.

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

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

EL NINO/SOUTHERN OSCILLATION (“ENSO”)

Multivariate ENSO Index (“MEI”)

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.

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.

Multidecadal PatternCold season Warm season

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

“Atlantic Multidecadal Oscillation”

(AMO)

Model

Model

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.

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

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.

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

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

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

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

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.

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.

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

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

Spectrum of Residual (1870-1999)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

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

TC #s vs T(t)

TC #s vs R(t)

AMO Influence on TCs?

CONCLUSIONS•AMO does not significantly project onto tropical North Atlantic SST

•Apparent multidecadal oscillation in tropical Aug-Oct Atlantic SST an artifact of late 20th 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.

“Atlantic Multidecadal Oscillation”

(AMO)

Observations

ModelObservations

“Pacific Decadal

Oscillation” (PDO)