The AMO Signal in Proxy and Instrumental Observations

1
The AMO Signal in Proxy and Instrumental
Observations

• Michael E. Mann
• Department of Meteorology/Earth and Environmental
  Systems Institute/Department of Geosciences
• Pennsylvania State University

CLIVAR Meeting on Multidecadal to Centennial
Global Climate Variability Honolulu Hawaii Nov
15, 2006
2
Climate Change Influence on the Destructive
Potential of Atlantic Hurricanes?
Katrina (Aug 28 05)
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
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
6
Climate Change?
natural variability?
OR
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
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 season
Warm season
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.
10
Multidecadal Pattern
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.
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Atlantic Multidecadal Oscillation (AMO)
Model
12
Model
13
(No Transcript)
14
Influence of AMO and Hurricanes?
15
Influences on tropical Atlantic SST
Global Mean Aug-Oct SST G(t) (Aug-Oct)
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.
16
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.
17
Estimation of AMO Influence
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.
18
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.
19
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.
20
Hansen, J. et al, Efficacy of climate forcings.
J. Geophys. Res. 110, D18104, doi10.1029/2005JD00
5776 (2005).)
21
Influences on tropical Atlantic SST
T(t) aG(t)bS(t)
aG(t)
bS(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.
22
Influences on tropical Atlantic SST
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.
23
Influences on tropical Atlantic SST
T(t) aG(t)bS(t) (full data)
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.
24
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.
25
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.
26
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.
27
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.

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AMO Influence on TCs?
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Implied Residual ASO MDR Warming
ASO MDR Aerosol cooling (GISS ModeleE)
Actual ASO MDR SST
Implied MDR ASO warming in absence of trop.
Aerosols based on GISS ModelE estimate
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Impact (red) of removing Atlantic from definition
of G(t)
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Impact (red) of removing Atlantic from definition
of G(t) (actual MDR SST series shown in black)
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Atlantic Multidecadal Oscillation (AMO)
Observations
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Observations
Model
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Pacific Decadal Oscillation (PDO)