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What makes a good polar climate model An IPCC perspective

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Title: What makes a good polar climate model An IPCC perspective


1
What makes a good polar climate model? An IPCC
perspective
  • Michael Winton
  • GFDL/NOAA
  • 13 April 2007
  • ECCO II Polar Meeting, MIT

2
What is an IPCC model?
  • Atmosphere 1-2o res. 20-40 levels
  • Ocean 1o res. 40-50 levels kpp gm mostly
    z-coord.
  • Sea ice (E)VP rheology leads gt1 level
  • gt20 models (13 countries) 2 flux-adjusted
  • Standard output data archived at PCMDI (gt250
    publications use this data)
  • IPCC model _at_ GFDL biggest/best we can run 5
    years/day

3
IPCC standard experiments
Figure K. Dixon
7 experiments 20 models 100 variables
lots of data
4
What do we want from the polar simulation?
  • Good simulation of local feedbacks and impacts
    ice-albedo feedback, polar amplification, sea ice
    retreat
  • Good simulation of ocean deepwater ventilation
    and its changes, ice sheet changes, carbon cycle
    changes

5
How well do the models simulate ocean circulation?
Gent et al (2006, J. Climate)
6
IPCC model climate change
TEMP 1xCO2
7
IPCC model climate change
TEMP 4xCO2
8
IPCC model climate change
SALT 1xCO2
9
IPCC model climate change
SALT 4xCO2
10
IPCC model climate change
DENSITY 1xCO2
11
IPCC model climate change
DENSITY 4xCO2
12
IPCC model climate change
CIRCULATION 1xCO2
13
IPCC model climate change
CIRCULATION 4xCO2
14
How well do the models simulate ocean circulation?
Russell et al (2006, J. Climate)
Does it matter?
Gregory et al (2005, GRL)
15
CM2.0
CM2.1
Stouffer et al (2005, J. Clim.)
Yes! The starting deep circulation seems to
matter to the response.
16
What changes in Atlantic overturning do they show?
Compare -1.9 Sv/decade (Wunsch/Heimbach 2006)
Schmittner et al (2005, GRL)
17
Why does the Atlantic overturning change?
CMIP diagnosis experiments
h2o forced
rad. forced
Gregory et al (2005, GRL)
18
How do sea ice albedo changes contribute to the
heat forced changes?
Reduced sea ice albedo
Increased CO2
Temperature
Age
Bitz et al (2006, J. Climate)
19
Another aspect of the North Atlantic adjustment
more heat to the Arctic
Holland and Bitz (2003, Climate Dynamics)
20
A tricky adjustment in the Southern Ocean the
wind change in the gap
Russell et al (2006, J. Climate)
21
Shallow Ocean
Atmosphere
Deep Ocean
CO2, Temperature rising rapidly shallow ocean
dominates uptake
Shallow Ocean
Atmosphere
Deep Ocean
CO2 stabilized, Temperature rising slowly deep
ocean dominates uptake
22
How well do the models do sea ice cover?
Parkinson et al (2006, JGR)
23
How does sea ice cover change?
Zhang and Walsh (2006, J. Climate)
Despite sea ice changes, 21st century Arctic
ocean climate change is linear!
24
What makes a good polar climate model?
  • Correct sensitivity
  • Correct climatology and variability
  • Credible process representations
  • Complete representation of processes
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