Why to Expect Medieval Climatic Change in
the Western Tropical Pacific:
A Large-scale Perspective
N. Graham
WET
HOLE 847A
DRY
Bermuda
MD-81
“1300 event”
PALMYRA
Yucatan
106-KL X
Moche
Quelccaya?
Naviashi
DRY
Workshop on Climate Changes in the Last 1500 years – Impacts on Pacific Island – Honolulu Nov. 2007
Co-Workers
Malcolm Hughes
Caspar Ammann
Kim Cobb
Marty Hoerling
Doug Kennett
Jim Kennett
Burt Rein
Lowell Stott
Peter Wigand
Taiyi Xu
Climatic Change, 2007:
83, 241-285
Collaborators
H. Diaz
R. Bradley
E. Wahl
M. Mann
T. Swetnam
M. Moseley
L. Thompson
M. Vuille
S. Starratt
J. Luterbacher
S. Brönnimann
Funding
NSF
NOAA
California Energy Comm.
L. Benson
P. Nunn
C. Long
J. Mohr
O. Davis
S. Anderson
P. Vorster
S. Brönnimann
E. Cook
S. Stine
What Is This Talk About?
Widely distributed proxy records suggest Medieval climate change
consistent with the presence of
persistent La Niña-like conditions in the tropical Pacific Ocean
If so, one would expect major climate changes in the western
tropical Pacific at the onset and termination of these conditions;
i.e. at ~ AD 500-800 and at ~AD 1200-1350
1. What do proxy records indicate about MCA conditions –
the western North America, the tropical Pacific.
2. Use numerical models to synthesize and extend the proxy data;
Describe inferred climate changes over the western Pacific at close of
MCA.
3. Look at evidence for the MCA as a global phenomena and consistency
(and inconsistency) with the “cool tropical Pacific” hypothesis.
PROXY RECORDS OF WESTERN US
HYDROLOGICAL VARIABILITY
A DRY MCA
+
-
FIRE-RELATED RECORDS
+ FIRE
- FIRE
DRY
PDSI: MCA - POST-MCA
DIFFERENCES
COVARIANCE PC #1
vs
PALMYRA CORAL δ18O
PDSI – Cook et al. (2004)
Palmyra – Cobb et al. (2003)
MERCED RIVER FLOW vs TREE RING “DROUGHT INDEX”
HOW DRY WERE THE MCA
DROUGHTS IN CALIFORNIA?
RECONSTRUCTION OF THE
MONO LAKE LOW STANDS
MERCED RIVER FLOW
(WEST SIDE SIERRA NEVADA
JUST WEST OF MONO LAKE)
RECONSTRUCTED MERCED RIVER FLOW
RECONSTRUCTED
FLOW DISTRIBUTIONS
RIVER
FLOW CUMULATIVE
DISTRIBUTIONS
MERCED RIVER FLOW vs MONO LAKE INFLOW
10th CENTURY
MCA
MODERN
PALEO-RECONSTRUCTION OF LAKE LEVELS
GIVES GOOD AGREEMENT WITH PROXY EVIDENCE
14C
dates
MODERN “NATURAL”
LEVEL
50-75 year offset between model
results and 14C tree death dates
LOW STANDS
FROM STINE (1994)
WHAT DID MCA CIRCULATION CHANGES LOOK LIKE?
PROXY-DRIVEN COMPOSITES
FROM COUPLED MODEL DATA
COMPOSITING BASED ON:
RECONSTRUCTED CALIFORNIA PRECIPITATION
and
COASTAL CALIFORNIA SST
“RECONSTRUCTED” MCA – POST-MCA WINTER DIFFERENCES
COUPLED MODEL – PROXY CONDITIONED COMPOSITES
NCAR CSM - BASED ON PROXY CALIFORNIA PRECIP. / SST
MCA (1000-1300) – LIA (1600-1900)
“RECONSTRUCTED” MCA – POST-MCA WINTER DIFFERENCES
COUPLED MODEL – PROXY CONDITIONED COMPOSITES
MPI – EC4 / HOPE - BASED ON PROXY CALIFORNIA PRECIP. / SST
MCA (1000-1300) – LIA (1600-1900)
PACIFIC MARINE PROXY DATA
PACIFIC MARINE PROXY RECORDS
CORRELATIONS
SST WITH NINO3 SST
COMPARE PALMYRA AND 106-KL PERU CORE
TRENDS SINCE 1880’s
FULL RECORD
GCM MCA SIMULATION
GCM FORCED WITH
PROXY-INFERRED
MCA TROPICAL PACIFIC
SST PATTERN
SST BASED ON THE
PALMYRA & MINDANAO
PROXY RECORDS
+
TYPICAL PATTERN
MODERN VARIABILITY
40+ ENSEMBLE MEMBERS
w/ IDEALIZED ENSO VARIABILITY
MODERN - MCA
DEC. - MARCH
MARCH - JUNE
Simulations by T. Xi and M. Hoerling, NOAA CDC;
Graham et al., Climatic Change, 2007
(c.f. Herweijer, Seager, and Cook, 2005)
MCA-LIA PRECIPITATION DIFFERENCES
TWO COUPLED MODELS (CSM & MPI)
PSR COMPOSITES BASED ON PALMYRA CORAL NINO3.4
DJFM PRECIP.: CLIMATOLOGY & LIA – MCA DIFFERENCE
MPI
CLIMATOLOGY
LIA – MCA
DIFFERENCE
MAGNITUDE OF MCA – LIA SEA LEVEL CHANGES
EXTRAPOLATION FROM TIDE GAUGE RECORDS
modern record suggests MCA ► LIA: southwestern Pacific decrease O150-250 cm
THE MCA ELSEWHERE:
SOME GLOBAL ASSOCIATIONS
GLOBAL PERSPECTIVE
WARMER
NAO+
EUROPE - MORE WESTERLY FLOW
STRONG AZORES HIGH
SUBTROP. WEST ATLANTIC WARM
WESTERN US DRY
CENTRAL AMERICAL DRY
C. EAST AFRICA DRY
NORTHERN PERU DRY,
INCREASED UPWELLING
CENTRAL CHILE DRY
WET
MCA-MODERN DIFFERENCES
Winter 500 hPa Heights & Surface Air Temperature
CCM3 MCA TROPICAL SST EXPERIMENT
WET
DRY
DRY
DRY
?
WET?
MEDIEVAL-MODERN:
DRY
DEC-MAR Z500 & SFC AIR TEMP – CCM3 AGCM
PALLCACOCHA, QUELCCAYA?
DRY
CHILE
MOROCCO
See Esper et al. GRL 2007
MOCHE CULTURE:
COASTAL NORTHERN PERU APPROXIMATELY 0-800 AD
WELL ENGINEERED CONTOUR FOLLOWING CANALS UP TO ~20 km
INTENSIVE AGRICULTURE
CULTURAL CENTERS
800 AD DISAPPEARS “AS A DISTINCTIVE CULTURAL PHENOMENOM”
- Dillehay and Kolata (2004)
MOCHE
CULTURE
DUNE FORMATION /
FLASH FLOODS
PALMYRA
NINO3.4
PERU RIVER DISCHARGE
CHIMU
cf Moseley et al. (1981); Shimada et al. (1991)
Summary
Widely distributed proxy records suggest Medieval climate change
consistent with the presence of
persistent La Niña-like conditions in the tropical Pacific Ocean
If so, one would expect major climate changes in the western
tropical Pacific at the onset and termination of these conditions;
i.e. at ~ AD 500-800 and at ~AD 1200-1350
1. What do proxy records indicate about MCA conditions –
the western North America, the tropical Pacific.
2. Use numerical models to synthesize and extend the proxy data;
Describe inferred climate changes over the western Pacific at close of
MCA.
3. Look at evidence for the MCA as a global phenomena and consistency
(and inconsistency) with the “cool tropical Pacific” hypothesis.
THANKS VERY MUCH!
What Is This Talk About?
MCA ≈ MCE ≈ MWP
1. More fully describing and quantifying MCA conditions in
western North America, especially California.
2. An attempt to describe the associated changes in circulation
patterns.
3. Examine the hypothesis that the changes above resulted from a
cool tropical Pacific.
4. Look at evidence for the MCA as a widespread phenomena and
consistency (and inconsistency) with the “cool tropical Pacific”
hypothesis.
Steen’s Mountain
THANK YOU!
SUMMARY
THE MWP – MCA
• CLEAR EVIDENCE OF GENERALLY DRY CONDITIONS, AND
PERIODS OF SEVERE DROUGHT IN WESTERN US.
• QUANTITATIVE RECONSTRUCTIONS INDICATE
CENTENNIAL-SCALE PRECIPITATION DEFECITS OF 20-25%.
• SUCH CHANGES WOULD BE DRIVEN BY MAJOR CHANGES
IN WINTER CIRCULATION CHANGES IN THE N. PACIFIC
• CONSISTENT EVIDENCE OF A COOL MCA TROPICAL PACIFIC.
SEEMS TO BE A LOT OF EVIDENCE THAT “SOMETHING”
IMPORTANT HAPPENED TO CHANGE CIRCULATION CHANGES.