1st Asia 2k Workshop
Nagoya, 2010
GLOBAL CLIMATE REORGANIZATION
MEDIEVAL TIMES and EFFECTS ON ASIA
N. Graham – Scripps / HRC
Collaborators & Contributors
C. Ammann – NCAR
D. Fleitmann – U. Bern
K. Cobb – Georgia Tech.
J. Luterbacher - Justus-Liebig-University
M.-A. Sicre, A. Mangini, A. Timmermann, J. Esper,
E. Xoplaki, H. Wanner, G. Massé, E. Cook, J. Conroy, L. Stott,
L. Thompson, M. Grosjean, R. Campbell, G. Wahl, L. Tan, H. Diaz,
A. Wanamaker, J. Conroy, E. Zorita, D. Verschuren, J. Russell,
R. Seager, V. Trouet, J. Scourse, A. Baker, T. Shanahan, R. Bradley
Grateful Thanks:
Oeschger Centre, U. Bern
PAGES
Asia 2K Organizing Committee
WHAT’S THIS TALK ABOUT?
CIRCULATION CHANGES DURING THE
MEDIEVAL CLIMATE ANOMALY (MCA)
– WHAT DO PROXY RECORDS INDICATE? - LOCAL CLIMATE CHANGE.
- WHAT CIRCULATION AND SST CHANGES ARE SUGGESTED?
- WHAT CHANGES IN SSTs MIGHT HAVE CAUSED THEM?
- COOLER TROPICAL PACIFIC & WARMER TROPICAL INDIAN OCEAN
- SOME COUPLED MODEL RESULTS.
- ASIAN CLIMATE VARIABILITY and the MCA-LIA TRANSITION
- RAPID SHIFTS AT THE ONSET AND CLOSE OF THE MCA.
MEDIEVAL CLIMATE
WHAT DO PROXY DATA SUGGEST?
WINTER
SUMMER
ANNUAL – MULTI- SEASON
PROXY INDICATIONS &
INFERRED CIRCULATION CHANGES
MEDIEVAL CLIMATE
WHAT DO PROXY DATA SUGGEST?
INFERRED CIRCULATION & CLIMATE CHANGES
*CIRCULATION
WARM
COOL
CHANGES FOR BOREAL WINTER
WARM?
Reduced
Nile
flood
level
gradual
SST
changes
GLOBAL NEAR-CONTEMPORANEOUS
MEDIEVAL CLIMATE CHANGES
~
POSSIBLE FORCING MECHANISMS
CHANGES IN BOUNDARY CONDITIONS
• PROBABLY NOT EXTRA-TROPICAL SSTs
- EXTRA-TROPICAL SSTs DO NOT PRODUCE ROBUST GLOBAL RESPONSE
- ... THEN TROPICAL SSTS
- REGIONAL ROLE FOR EXTRA-TROPICAL SSTs
• LIKELY NOT ONLY A COOL TROPICAL PACIFIC
- SOME CLEARLY EVIDENT CHANGES NOT CONSISTENTLY REPRODUCED1
• LATE 20th CENTURY INDIAN OCEAN WARMING OFFERS CLUES
- AGCM SIMULATIONS REPRODUCE DISTINCTIVE FEATURES2:
 STRONGER NAO
 WEAKER ALEUTIAN LOW
1) Graham et al. 2007; Seager et al. 2007, 2008)
2) Bader and Latif, 2003, 2005; Hurrell and Hoerling, 2003; Hoerling and Hurrell, 2003
INDIAN OCEAN WARMING EXPERIMENTS
• NCAR CCSM – FULL PHYSICS COUPLED MODEL (~ 3.75º)
• PRE-INDUSTRIAL GHG
SERIES OF EXPERIMENTS
• 0.3-0.8C WARMING – via increased surface shortwave
• WARMING INDIAN OCEAN and WESTERN PACIFIC, or
• WARMING INDIAN OCEAN ONLY
• 48-50 YEAR EXPERIMENTS + CONTROL RUN DATA
- RESULTS FROM ONE EXPERIMENT SHOWN HERE
- ALL EXPERIMENTS SHOW SIMILAR RESULTS
CCSM WITH WARMER INDIAN OCEAN vs CONTROL
DEC.-MARCH:
PRECIPITATION (%) & SEA LEVEL PRESSURE (hPa)
DID MEDIEVAL WINTER CIRCULATION LOOK LIKE THIS?
DRIER:
WESTERN US
S. EUROPE – MED.
NW AFRICA
SW / CENTRAL ASIA
PERU / ECUADOR
EQ. PACIFIC
WETTER:
NW EUROPE
CHINA (SUMMER)
SEA LEVEL PRESSURE:
LARGE SCALE RIDGING
NE PACIFIC -> MED. ->
SW ASIA
NAO+
PRECIP. (% CLIMATOLOGY)
LIKE OTHER MODELS
Graham et al., Clim. Dyn. accepted
CCSM - COUPLED WITH WARMER INDIAN OCEAN vs CONTROL
DEC.-MARCH: TEMPERATURE (less global average)
- NORTH ATLANTIC SST – SEA ICE
-INDUCED TROPICAL PACIFIC COOLING
CCSM WITH WARMER (0.4 - 0.8C) INDIAN OCEAN vs CONTROL
JJAS: PRECIPITATION (%) & SEA LEVEL PRESSURE (hPa)
-DRY PARTS OF EQ> AFRICA - ETHIOPIAN PLATEAU, NW IND. OCEAN
-MIXED SIGNAL THROUGH INDIAN & EAST ASIAN MONSOON REGIONS
PRECIP. (% CLIMATOLOGY)
CCSM WITH WARMER INDIAN OCEAN vs CONTROL
JJAS: TEMPERATURE
NOTE ATLANTIC SST PATTERN
ARABIAN SEA WIND STRESS - UPWELLING
INDIAN and EAST ASIAN MONSOONS
NOT MUCH MCA SIGNAL - 15th CENTURY ARIDITY
S. OMAN
COASTAL PAKISTAN
EAST INDIA
S. CHINA
CENTRAL CHINA
EASTERN CHINA
EVIDENCE FOR
RAPID MCA CLIMATE SHIFTS
HIGH LATITUDE N. ATLANTIC
SEA ICE: SW GREENLAND
more ice
• SEA ICE REDUCTION – SW GREENLAND
• SEA ICE ABSENCE – NORTH ICELAND
• 1˚C SUMMER WARMING – NORTH ICELAND
SEA ICE: N. ICELAND
SST: N. ICELAND warmer
• INCREASED MONSOON RAINFALL
EQUATORIAL PACIFIC
wetter
PRECIP:
CEN. CHINA
• WARMER WEST – LIKELY FORCED BY ATM.
• COOLER EAST
SST: FAR WEST. EQ. PAC.
more
FIRE
CEN. CALIF.
warmer
SST: EAST. EQ. PAC.
low
CENTRAL CHINA
CALIFORNIA SIERRA NEVADA
• MORE FIRE – DRY WINTERS, WARM SUMMERS?
• NOT SO ABRUPT IN WINTER PRECIP.
EQ. AFRICA - IVORY COAST & RIFT VALLEY LAKES
•REDUCED RAINFALL
• NOT APPARENT IN GULF of GUINNEA SSTs
LAKE LEVEL:
GHANA
less
PRECIP: YUCATAN
YUCATAN
• INCREASED RAINFALL AT START OF MCA
• NO POST-MCA REVERSAL
• NOT CARIBBEAN - MESO-AMERICA WIDE
SUMMARY
 EVIDENCE FOR PERSISTENT SHIFTS IN GLOBAL CIRCULATION PATTERNS
- WEAKER ALEUTIAN LOW – STRONGER NAO & RELATED REGIONAL CLIMATE CHANGES
- WARM EXTRA-TROP. NORTH ATLANTIC, REDUCED SEA ICE
- COOL EASTERN & CENTRAL EQUATORIAL PACIFIC – WARM IN WEST
- ARID EQUATORIAL AFRICA, AROUND NW INDIAN OCEAN
- MIXED (~MOIST) INDIAN / EAST ASIAN MONSOONS – EARLY LIA MORE DRAMATIC
 COUPLED MODEL - PRESCRIBED WARMER INDIAN / WEST PACIFIC
- REPRODUCES MANY PROXY-INDICATED CHANGES
- HYDROCLIMATE CHANGES INDUCED BY CIRCULATION SHIFTS
- MECHANISMS FOR INDIAN OCEAN-FORCED CIRCULATION CHANGES WELL UNDERSTOOD
 EVIDENCE FOR SHARP (DECADAL TIME SCALE) ONSET AND CLOSE OF MCA
- SOME WIDELY DISTRIBUTED PROXIES – SENSITIVE REGIONS & CLIMATE INDICATORS
- CLEARLY SEEN IN TROPICAL PACIFIC SSTS (LESS SO IN TROPICAL ATLANTIC)
 CAUSES?
- SOLAR, VOLCANIC, SEA ICE INSTABILITY, MOC, COUPLED FEEDBACKS….
- e.g., CLEMENT, MANN, MEEHL, BITZ, MERRYFIELD, SEAGER, SHINDELL, TIMMERMANN
THANK YOU !
SUMMARY
RESPONSE TO WARMER INDIAN OCEAN
 CONSISTENT WITH MANY PROXY RECORDS AROUND THE PLANET
* EXPANDED SUB-TROPICAL HIGH
- WEAKER ALEUTIAN LOW – ARID WESTERN US
- ENHANCED NAO – RIDGING INTO CENTRAL ASIA
* DRY / COOL TROPICAL PACIFIC (LIKELY NOT COOL ENOUGH, SUMMER)
* ARIDITY AROUND PERIPHERY OF W. & NW INDIAN OCEAN – NILE, OMAN
* DRY CENTRAL AMERICA
 CAUSES?
* SOLAR FORCING – SHINDELL, MANN, MEEHL, CLEMENT (TOP DOWN, BOTTOM UP)
* THERMOHALINE – TIMMERMANN, MANN, SEAGER
* PURELY EXTERNAL / INTERNAL / MIXED
CIRCULATION CHANGES FOR WINTER
H
L
*
*
H
DIAGNOSE SST FORCING FOR GLOBAL CIRCULATION
CHANGES OVER LAST MILLENIUM
WHAT DO PROXY DATA PROXY SUGGEST?
CIRCULAITON CHANGES FOR WINTER
CCSM WITH WARMER (0.4 - 0.8C) INDIAN OCEAN vs CONTROL
DJFM: PRECIPITATION & SEA LEVEL PRESSURE
- WARMING NORTH OF ICELAND (SEA ICE RETREAT)
- NAO-like SST PATTERN CONSISTENT WITH PROXY RECORDS