Comparisons of Observed Paleoclimate and Model-Based Studies of Climate Changes Over the Past Two Millennia

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Comparisons of Observed Paleoclimate and
Model-Based Studies of Climate Changes Over the
Past Two Millennia
Michael E. Mann
Department of Environmental Sciences, University
of Virginia, Charlottesville, VA
Keith Briffa Climatic Research Unit University of
East Anglia, UK
Collaborators B. Adams, C. Ammann, R. Bradley
M. Cane A. Clement, T. Delworth M.K. Hughes,
T. Osborn P. Jones, S. Rutherford G. Schmidt
D. Shindell S. Zebiak
CLIVAR 2004Baltimore, MD June 23, 2004
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Mann, M.E., Ammann, C., Bradley, R.S., Briffa,
K., Crowley, T.J., Hughes, M.K., Jones, P.D.,
Oppenheimer, M., Osborn, T.J., Overpeck, J.T.,
Rutherford, S., Trenberth, K.E., Wigley,
T.M.L., On Past Temperatures and Anomalous late
20th Century Warmth, Eos, 84, 256-258, 2003
MODIFIED BoreholesRutherford and Mann (2004)
Crowley Lowery (updated)
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Greater variability in extratropics and summer!
Mann, M.E., Ammann, C., Bradley, R.S., Briffa,
K., Crowley, T.J., Hughes, M.K., Jones, P.D.,
Oppenheimer, M., Osborn, T.J., Overpeck, J.T.,
Rutherford, S., Trenberth, K.E., Wigley,
T.M.L., On Past Temperatures and Anomalous late
20th Century Warmth, Eos, 84, 256-258, 2003
MODIFIED BoreholesRutherford and Mann (2004)
Crowley Lowery (updated)
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Empirical Proxy-Based Climate Reconstructions
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1. Sensitivity to scaling/calibration
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2. Sensitivity to target region and season
Comparison is difficult because each
reconstruction uses a different season, region
and calibration period
Example shows a comparison after re-scaling every
series against annual or warm-season temperature
averaged over all land north of 20N over a
common 1881-1960 period
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2. Sensitivity to target region and season
Comparison between Briffa et al. NH extratropical
warm-season NH mean temperature reconstruction
with RegEM reconstruction
(a) unmasked
Rutherford, S., Mann, M.E., Osborn, T.J.,
Bradley, R.S., Briffa, K.R., Hughes, M.K., Jones,
P.D., Proxy-based Northern Hemisphere Surface
Temperature Reconstructions Sensitivity to
Methodology, Predictor network, Journal of
Climate (in revision), 2004.
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2. Sensitivity to target region and season
Comparison between Briffa et al. NH extratropical
warm-season NH mean temperature reconstruction
with RegEM reconstruction (a) unmasked (b)
masked
Rutherford, S., Mann, M.E., Osborn, T.J.,
Bradley, R.S., Briffa, K.R., Hughes, M.K., Jones,
P.D., Proxy-based Northern Hemisphere Surface
Temperature Reconstructions Sensitivity to
Methodology, Predictor network, Journal of
Climate (in revision), 2004.
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2. Sensitivity to target region and season
Comparison between Briffa et al. NH extratropical
warm-season NH mean temperature reconstruction
with RegEM reconstruction (a) unmasked (b)
masked (c) based on Esper et al (2002) locations
only
Rutherford, S., Mann, M.E., Osborn, T.J.,
Bradley, R.S., Briffa, K.R., Hughes, M.K., Jones,
P.D., Proxy-based Northern Hemisphere Surface
Temperature Reconstructions Sensitivity to
Methodology, Predictor network, Journal of
Climate (in revision), 2004.
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Documentary evidence of change in seasonal range
2. Sensitivity to target region and season
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Model/Data Comparisons
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Detection of unusual warming trends
Compare observed trends during the 20th century
with the95th percentile of pre-20th century
natural variability trends
Unusual warming is detectedfor cases with
observed warmingexceeding all three 95th
percentilesof natural variabilityThe
temperature in this exampleis extended summer
temperatureaveraged over all land north of 20N.
Three estimates of natural variability Reconst
ruction1 (from tree-rings withlow-frequency
standardisation) Reconstruction2 (from
tree-rings with traditional standardisation) Mode
l (1000-yr HadCM3 control run)
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CLIMATE FORCINGS
Volcanism
Solar
Natural
Crowley, T.J., Causes of Climate Change Over the
Past 1000 Years, Science, 289 270-277, 2000.
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CLIMATE FORCINGS
Anthropogenic
Industrial Aerosols
Greenhouse Gases
Climate Change 2001 The Scientific Basis,
Houghton, J.T., et al. (eds.), Cambridge Univ.
Press, Cambridge, 2001
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Jones, P.D., Mann, M.E., Climate Over Past
Millennia, Reviews of Geophysics, 42, RG2002,
doi10.1029/2003RG000143, 2004.
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Northern extratropics summer temperature
Last 500 years, 10-year smoothing
Tree-ring densityreconstruction
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European Winter Cooling During the Little Ice Age
Empirical
LIA winter cooling in Europe associated with an
NAO trend due to solar irradiance changes,
interacting w/ stratospheric atmospheric dynamics
and chemistry
NASA/GISS Model
Shindell, D.T., Schmidt, G.A., Mann, M.E., Rind,
D., Waple, A., Solar forcing of regional climate
change during the Maunder Minimum, Science, 294,
2149-2152, 2001.
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Annual average late 17th vs late 18th Century
Temperature change
Proxy based reconstruction
GCM Solar Volcanic patterns
Shindell, D.T., Schmidt, G.A., Miller, R., Mann,
M.E., Volcanic and Solar forcing of Climate
Change During the Pre-Industrial era, Journal of
Climate, 16, 4094-4107, 2003.
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Volcanic Radiative Summer Cooling
Ensemble average summer (Jun-Aug) surface
temperature response following eruption of
Pinatubo.
Shindell, D.T., Schmidt, G.A., Miller, R., Mann,
M.E., Volcanic and Solar forcing of Climate
Change During the Pre-Industrial era, Journal of
Climate, 16, 4094-4107, 2003.
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Volcanic Winter Dynamical Warming
Ensemble average winter (Dec-Feb) surface
temperature response following eruption of
Pinatubo.
Shindell, D.T., Schmidt, G.A., Miller, R., Mann,
M.E., Volcanic and Solar forcing of Climate
Change During the Pre-Industrial era, Journal of
Climate, 16, 4094-4107, 2003.
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Mid-Latitude Summers
Greater variability?
Esper, J., Cook, E.R., Schweingruber, F.H.,
Low-Frequency Signals in Long Tree-Ring
Chronologies for Reconstructing Past Temperature
Variability, Science, 295, 2250-2253, 2002.
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Mid-Latitude Summers
Greater variability?
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Simulated and reconstructed changes in seasonal
range
ECHAM4-HOPE
Thick lines documentary record
Thin lines
HadCM3
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Simulated and reconstructed changes in seasonal
range
ECHAM4-HOPE
Thick lines documentary record
Thin lines
HadCM3
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Volcanic Forcing of El Nino?
Adams, J.B., Mann, M.E., Ammann, C.M., Proxy
evidence for an El Nino-like Response to Volcanic
Forcing, Nature, 426, 274-278, 2003.
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Theoretical mechanism for natural radiative
forcing of El Nino
Cane, M.A., A.C. Clement, A. Kaplan, Y. Kushnir,
D. Pozdnyakov, R. Seager, S.E. Zebiak, and R.
Murtugudde, Twentieth-Century Sea Surface
Temperature Trends, Science, 275, 957-960, 1997.
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Theoretical mechanism for natural radiative
forcing of El Nino
Combined response to Solar Volcanic Forcing
Palymra coral isotopes (standardized to have same
mean and standard deviation as Nino3 composite
series)
Ensemble mean Nino3 (100 realizations of CZ model)
40 year smooth
Mann, M.E., Cane, M.A., Zebiak, S.E., Clement,
A., Volcanic and Solar Forcing of El Niño Over
the Past 1000 Years, in revision, 2004.
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Theoretical mechanism for natural radiative
forcing of El Nino
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Theoretical mechanism for natural radiative
forcing of El Nino
Courtesy of E.Cook
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CONCLUSIONS

• Proxy reconstructions and model simulations both
  suggest that late 20th century warmth is
  anomalous in the context of the past 1000-2000
  years

• Primary source of differences between various
  reconstructions appear to be related to issues of
  seasonality and spatial representativeness

• Important differences between estimates of
  extratropical and full (combined tropical and
  extratropical) hemispheric mean temperature
  changes in past centuries appear consistent with
  seasonal and spatially-specific responses to
  climate forcing.

• Forced changes in large-scale atmospheric
  circulation such as the NAO, and internal
  dynamics related to El Nino, may play an
  important role in explaining regional patterns of
  variability and change.

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Northern extratropics summer temperature
Last 500 years, 10-year smoothing
Last 1000 years, 20-year smoothing
Tree-ring densityreconstruction
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Simulated changes in seasonal range over last 150
years