Polar Amplification of Climate

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Polar Amplification of Climate
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Polar Amplification of Climate Change in Coupled
ModelsHolland, M. M., Bitz, C. M. Climate
Dynamics, Vol. 21, Issue 3-4, pp.221-232, Sept
2003.

• Analysis of northern hemisphere polar
  amplification of climate by means of comparison
  amongst a group of climate models
• Surface warming in the arctic
• Magnitude
• Distribution
• Seasonality

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Sea-ice physics for models with high polar
amplification
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Whats going on with BRMC?
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Variables

• Sea ice
• Extent
• Thickness
• Snow coverage on land
• Cloud coverage
• Ocean heat transport

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Sea Ice Extent

• Ice extent and latitude of maximum warming are
  significantly correlated, R-.80
• Models with larger ice extents have a tendency to
  have maximum warming at lower latitudes, why is
  this?

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Sea Ice Extent

• Larger ice extents generally cause higher global
  sensitivity because the earth has more available
  ice to melt (only for models with low-moderate
  polar amplification) why not high amplification
  models?
• No significant correlation between ice extent and
  normalized warming, considering all models
  together

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Sea Ice Thickness

• More highly correlated to normalized warming than
  sea ice extent, R-.40

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Sea Ice Thickness

• Suggests that because thin ice is more easily
  melted, warming causes greater loss of ice extent
• Greater albedo feedback and loss of insulation
  between ocean and atmosphere amplify the warming
• Still, weak correlations suggest some other
  factors may be at work...

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Snow Coverage on Land

• No significant correlation between snow coverage
  and normalized warming, considering all models
  together
• However, as with ice extent, a significant
  correlation exists among the models with
  low-moderate polar amplification, R.67

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Snow Coverage

• Correlation (among low-moderate amplification
  models) is probably a result of the snow coverage
  on land being highly correlated to the extent of
  ice, and not indicative of the snow extent
  influencing the polar amplification of warming

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Cloud coverage

• Does increased cloud coverage have a positive or
  negative effect on polar amplification of
  warming?

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Cloud Coverage Temperature Feedbacks
High Clouds
Low Clouds
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Summer Clouds

• Changes in ice-albedo, and thus absorbed solar
  radiation, did not result in changes in cloud
  cover during summer
• However, the high amplification models do have a
  tendency to have increased summer cloud cover

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Winter Clouds

• Also, decreased winter cloud cover in control
  climate is correlated to higher polar
  amplification, R-.50
• Problem model bias? Control climate cloud
  conditions related to change in clouds, R-.76,
  Lower levels of original cloud cover allow for
  greater change
• Larger winter cloud cover changes correlated to
  higher amplification, R.74,

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Cloud Coverage

• Problems
• No distinction between high and low clouds
• Dont know enough about cloud relationships and
  feedbacks
• Dont have data from all of the models

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Ocean Heat Transport
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ECH-3
CCSM
CERF
CCSR
MRI
BMRC
CCC
GFDL-A
GISS
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CCSM
ECH-3
CERF
CCC
CCSR
BMRC
GISS
MRI
GFDL-A
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Ocean Heat Transport

• Control climate ocean heat transport and change
  in transport are both significantly correlated to
  polar warming

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Ocean Heat Transport

• Because increased heat transport by the ocean is
  correlated with both sea ice extent and
  thickness, it seems possible that this then
  decreases surface albedo by melting sea ice and
  amplifies warming

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Conclusion

• Possible factors affecting increased polar
  amplification based on these models
• Thin sea-ice cover
• Increased ocean heat transport to poles
• Increase in winter cloud cover

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Conclusion

• Further work is needed within single models to
  clarify and better understand the relationships
  suggested by this group of models
• From this study it is clear that very accurate
  depictions of current sea ice characteristics,
  such as extent and thickness, are necessary to
  receive valid data concerning the arctic
  responses to increased warming by greenhouse gases

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Arctic pictures
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