1976-77 Climate Shift in the Pacific and its consequences

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The 1976-77 North Pacific Ocean event A unique
climate shift, natural decadal variability, or
global warming?
Janelle Fleming Interdisciplinary
Seminar September 16, 1998
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Outline

• Description of Regime Shift
• Physical characteristics
• Climatological characteristics
• Biological characteristics
• Interpretations
• I. Unique series of events
• II. Part of decadal variation
• III. Global warming trend
• Conclusions

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The Region
Tomczak and Godfrey (1994)
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The Shift

• Descriptive Data

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The ShiftPhysical Indicators

• Begins during winter months of 1976-1977
• Altered Patterns of Upper-Ocean SST
• Cooler SST in Central Pacific
• Warmer SST along coast of North America
• Warmer SST in central and eastern tropics
• Altered Temperature Patterns in water column

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SST anomalies - North Pacific
Graham, N.E. (1994)
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SST anomalies-North Pacific
Winters (1980-85) minus (1968-73)
Venrick, et al. (1987)
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SST anomalies-the tropics
Difference Map Epoch 2 - Epoch 1
Graham, N.E. (1994)
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Water Column Temp Anomalies
Temp Difference (1978-89) and (1971-76) at 100m
Deser, et al (1996)
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Water Column Temp Anomalies
Temp Difference (1979-90) and (1972-77) at 250m
Deser, et al (1996)
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Water Column Temp Anomalies
Temp Difference (1980-91) and (1972-78) at 400m
Deser, et al (1996)
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The ShiftClimate Indicators

• Aleutian Low shifts and intensifies
• Increased storminess
• Westerly winds shift and intensify
• Organized convection over the tropical Pacific
  shifts

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700 hPa heights - North Pacific
Graham, (1994)
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North Pacific Sea Level Pressure
Trenberth (1990)
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The ShiftWind Patterns
Deser, et al, (1996)
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Organized Convection - OLR
Difference Maps Epoch 2 - Epoch 1
Graham (1994)
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Organized Convection - HRC
Difference Map Epoch 2 - Epoch 1
Graham (1994)
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The ShiftBiological Indicators

• Chlorophyll a concentration
• vertically averaged
• mean concentration doubles after 1976
• Species Richness on a reef system off California
  declined by 15-25.

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Chlorophyll a Concentrations
Venrick, et al, (1987)
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Species Richness
Holbrook, et al (1997)
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The ShiftBroad based evidence

• 40 environmental variables
• distributed throughout the Pacific basin
• Variables include
• Number of Great Basin Canada goose nests
• Sea Ice extent
• Salinity
• upwelling
• commercial dungeness crab production
• salmon catch

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The Shift Step-wise change
Ebbesmeyer, et al, 1991
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Interpretations

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I. Unique Event

• Miller et al (1994)
• Used a layered ocean GCM
• forced with total surface heat flux anomalies
• forced with wind stress anomalies
• reproduced SST change
• Large advective effects
• Long term heat flux variations
• Caused by unique atmospheric anomalies

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I. Unique Event
Miller et al. (1994)
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I. Unique Event

• Graham, et al (1994)
• Used evolving general circulation model (GCM)
• Forced with observed SSTs
• abrupt change in SST in equatorial Pacific lead
  to the shift

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I. Unique Event
700 hPa difference Maps winters
(1977-82)-(1971-76)
Graham, et al(1994)
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II. Decadal Variation

• Latif and Barnett (1994,1996)
• mid-latitude SSTs interact with mid-latitude
  atmosphere
• Drives a decadal cycle of 20 yrs

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II. Decadal Variation
Latif and Barnett (1996)
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II. Decadal Variation

• Gu and Philander (1997)
• Tropical SST affects the mid-latitudes through
  the atmosphere
• Mid-latitudes affect the tropics through the ocean

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II. Decadal Variation
Gu and Philander, (1997)
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II. Decadal Variation

• Mantua et al (1997)
• Create a Pacific (Inter-) Decadal Oscillation
  (PDO) index.
• Correlate PDO with salmon catch

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II. Decadal Variation
Mantua et al (1997)
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Decadal Variability
Mantua, et al (1997)
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II. Decadal Variation

• French Frigate Shoals in the Western Hawaiian
  Islands
• Mixed layer depths increase
• Response to climate change in higher trophic
  levels
• spiny lobsters (2nd trophic level)
• reef fishes (3rd trophic level)
• seabirds and monk seals (top trophic level)

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II. Decadal Variation
Polovina, et al (1994)
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III. Global Warming

• California Coastal System
• 80 decrease in zooplankton biomass
• Correlated linear increase in SST

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III. Global warming
Roemmich and McGowan (1995)
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III. Global Warming

• Pelagic Bird population decline of 40 since 1987
• Correlation with long-term increase in SST

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III. Global Warming
Veit, et al (1996)
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III. Global Warming

• Latif and Barnett (1994)
• linear trend in SST in both observation and model
  data

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III. Global Warming
Latif et al (1997)
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Conclusions

• An abrupt shift did occur in the mid-70s
• Shift is part of interaction of cycles
• ENSO cycle in the tropics
• Aleutian Low cycle in the extratropics
• Inconclusive data as to anthropogenic influence

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Socio-historical perspective
Thank you Dr. Luettich, Dr. Werner, Dr. Shay, J.
Fleming, Dr. McNinch, J. Hench, J. Dyble, C.
Conoway, G. Johnson, M. Harrington, D. Whitehall