IPCC Model Projections of North Pacific Climate Variability

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Expected Changes in the Climate Forcing of
Alaskan Waters in Late Summer/Early Fall

• Nicholas A. Bond1
• James E. Overland2 and Muyin Wang1
• 1 University of Washington/JISAO
• 2 NOAA/PMEL

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Analysis of Model Output

• Ascertain parameters crucial to the ecosystem
  and/or the species of interest
• Use monthly mean model output for direct
  projections (when appropriate based on type and
  scale of parameter)
• Determine proxies or empirical relationships for
  parameters that must be projected indirectly

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Models Contributed to IPCC AR4
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Bayesian Model Averaging (BMA)

• Considers an ensemble of plausible models
• Forecast PDF estimated through weighting the PDFs
  of the individual models, with weights determined
  by posterior model probabilities
• BMA possesses a range of properties optimal from
  a theoretical point of view works well in
  short-term weather prediction

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Procedure

• Retain IPCC models that replicate the PDO in
  their 20th century hindcasts
• Select parameter(s) and criteria (mean, variance,
  trend?) for the region/ecosystem of interest
• Compute errors (distances) between observations
  and hindcasts for the latter half of the 20th
  century
• Compute weights based on Wi exp(-Di/Dm)
• Calculate PDFs of projections (ensemble weighted
  means and variances)

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Zooplankton on the Bering Sea Shelf - Coyle et
al. (2008) Compared water properties and
zooplankton abundance and community structure
between a cold and warm year 1999 2004 -----
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----------- Upper Temp 7.0 12.6 (deg.
C) Lower Temp 2.0 3.2 Oithona 348 1633
(/m3) Pseudocalanus 404 1211 Calanus
44 0 Thysanoessa 0.33 0.05
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CCMAT_63
MIROC_M
MRI
UKHAD_C
GFDL21
GFDL20
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Predicted Std. Dev.
Predictive Variance
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SLP Anomalies Strong Wind Mixing Years SLP
Anomalies Weak Wind Mixing Years
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Change in SLP 2040s vs 2000s
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Coastal Gulf of Alaska

• Focus on Alaska Coastal Current (ACC)
• Transports related to along-coast winds
• Baroclinity related to runoff of freshwater

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Weighted Ensemble Mean
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Downwelling
Weighted Ensemble Mean
Upwelling
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Summary

• Present generation coupled GCMs are starting to
  be used for making projections for Alaskan marine
  populations
• Bayesian model averaging represents a method for
  constructing model means and uncertainties
• Bering Sea shelf - SST warming of 2 C by 2050
  Weak trend of greater storminess
• Coastal Gulf of Alaska - Minimal net change in
  dynamic forcing of runoff Weak trend of greater
  upwelling

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Final Remarks

• From present to mid-21st century, climate change
  liable to be dominated by thermodynamic effects
  as opposed to dynamic effects (e.g., winds)
• Hybrid model simulations using present-day
  physics (modified to account for warming) and
  dynamic biology may be feasible.
• The results from these kinds of simulations
  should complement those from vertically-integrated
  numerical models with full dynamics.