Transcript No Slide Title

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 2004
Baltimore, MD
June 23, 2004
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:
Boreholes—Rutherford and Mann (2004); Crowley & Lowery (updated)]
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:
Boreholes—Rutherford and Mann (2004); Crowley & Lowery (updated)]
Empirical Proxy-Based
Climate Reconstructions
1. Sensitivity to scaling/calibration
Osborn, T.J., and K.R. Briffa, Comments on the paper of R. N. Harris and D.S.
Chapman "Mid-latitude (30'N-60'N) climate warming inferred by combining borehole
temperatures with surface air temperatures", Geophysical Research Letters, 29 (16),
(45)1-2, 2002.
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 20°N
over a common 1881-1960 period
Mann1999
(land north of 20N extracted
from spatial reconstructions)
Esper2002
www.cru.uea.ac.uk/cru/projects/soap/
Briffa2000
Jones1998
Briffa2001
From Briffa, Osborn and Schweingruber (2003) Glob Planet
Change
2. Sensitivity to
target region and
season
Comparison between Briffa
et al. NH extratropical warmseason 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.
2. Sensitivity to
target region and
season
Comparison between Briffa
et al. NH extratropical warmseason 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.
2. Sensitivity to
target region and
season
Comparison between Briffa
et al. NH extratropical warmseason 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.
2. Sensitivity to target region and season
Documentary evidence of change in seasonal range
Manley/Parker
Brazdil
Van Engelen
Wang
Pfister
Wang
www.cru.uea.ac.uk/cru/projects/soap/
From Jones, Osborn and Briffa (2003) J Geophys Res
Model/Data Comparisons
Detection of “unusual” warming trends
Compare observed trends during the 20th century with the
95th percentile of pre-20th century “natural variability” trends
Observedwarming
warmingisover
“Unusual”
detected
various
ending in
2000
for
casesperiods
with observed
warming
exceeding all three 95th percentiles
of “natural”
variability
Three
estimates
“natural” variability:
1991-2000of
trend
1966-2000 trend
The
temperature
in this
examplewith
Reconstruction1
(from
tree-rings
1936-2000
trendtemperature
is extended
summer
low-frequency
standardisation)
1901-2000
averaged
over alltrend
land north of 20N.
Reconstruction2 (from tree-rings with
traditional standardisation)
Model (1000-yr HadCM3 control run)
www.cru.uea.ac.uk/cru/projects/soap/
Analysis from Tim Osborn (CRU, UEA, UK)
CLIMATE FORCINGS
Volcanism
1000
1200
1400
1600
1800
Solar
Natural
Crowley, T.J., Causes of
Climate Change Over the
Past 1000 Years, Science,
289 270-277, 2000.
2000
CLIMATE FORCINGS
Anthropogenic
Greenhouse
Gases
Industrial
Aerosols
Climate Change 2001: The
Scientific Basis, Houghton, J.T.,
et al. (eds.), Cambridge Univ.
Press, Cambridge, 2001
Jones, P.D., Mann, M.E., Climate
Over Past Millennia, Reviews of
Geophysics, 42, RG2002,
doi:10.1029/2003RG000143, 2004.
Northern extratropics summer temperature
Last 500 years, 10-year
smoothing
Tree-ring density
ECHAM4-HOPE
HadCM3 reconstruction
www.cru.uea.ac.uk/cru/projects/soap/
Observations
Data comparison from Tim Osborn (CRU, UEA, UK)
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, 21492152, 2001.
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, 40944107, 2003.
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.
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.
Mid-Latitude Summers
Greater variability?
Esper, J., Cook, E.R.,
Schweingruber, F.H., LowFrequency Signals in Long
Tree-Ring Chronologies for
Reconstructing Past
Temperature Variability,
Science, 295, 2250-2253,
2002.
Mid-Latitude Summers
Greater variability?
1000
1200
1400
1600
1800
2000
Simulated and reconstructed changes in
seasonal range
Thick lines = documentary record
www.cru.uea.ac.uk/cru/projects/soap/
Thin lines =
ECHAM4-HOPE
HadCM3
Data comparison from Tim Osborn (CRU, UEA, UK)
Simulated and reconstructed changes in
seasonal range
Thick lines = documentary record
www.cru.uea.ac.uk/cru/projects/soap/
Thin lines =
ECHAM4-HOPE
HadCM3
Data comparison from Tim Osborn (CRU, UEA, UK)
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.
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.
Theoretical mechanism for natural
radiative forcing of El Nino
Combined response to Solar
+Volcanic Forcing
Ensemble mean
Nino3 (100
realizations of CZ
model)
40 year
smooth
Palymra coral
isotopes (standardized
to have same mean and
standard deviation as
Nino3 composite series)
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.
Theoretical mechanism for natural
radiative forcing of El Nino
Theoretical mechanism for natural
radiative forcing of El Nino
Courtesy of E.Cook
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.
Northern extratropics summer temperature
1000years,
years,10-year
20-year
Last 500
smoothing
Tree-ring density
ECHAM4-HOPE
HadCM3 reconstruction
www.cru.uea.ac.uk/cru/projects/soap/
Observations
Data comparison from Tim Osborn (CRU, UEA, UK)
Simulated changes in seasonal range over last
150 years
www.cru.uea.ac.uk/cru/projects/soap/
Analysis from Tim Osborn (CRU, UEA, UK)