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The Demise of the Arctic Sea Ice

Jeff Ridley

David Simonin

Jason Lowe

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Climate Change

HadCM3 Climate at 4xCO22% per year increase in CO2 for 70 yearsStabilise at 4xCO2 for 1000 yearsGlobal temperature rise of 5°CTHC decreases by 35% but recovers to just 10% downPrecipitation over Arctic and river runoff up by 20%Greenland runoff from surface melt 10% of total runoff

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12

10

8

6

4

2

0

Arc

tic ic

e ar

ea (

x 10

6 k

m2)

Climate at 4xCO2

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Basic state 1xCO2 Basic state 4xCO2

High state Low state

Annual cycle

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Possible Causes

Change in atmospheric circulationbut, pressure system constant- no change in AO

Change in surface forcingbut, cloud cover increase compensates for ice

declineChange in THC and ocean heat transport

THC variable but no shift in regimeInternal redistribution of oceanic heat

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61 73 86 82 69

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Dep

th (

m)

Latitude

TREND

0.5

1

1.5

2

2.5

3

3.5

4

x 10-3

Ocean Warming

Cross-section across pole along 45° longitude

Degrees warmingper 1000 years

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Arctic Ocean Temperature at 100m

1xCO2 4xCO2

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Correlation between 90m ocean temperature and sea-ice cover

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-2 0 2 4 6 8

Ocean Temperature (°C)

20

50

120

300

650

Dep

th (

m)

Ice

Con

cent

ratio

n

Ocean time series (Beaufort Gyre)

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Tem

pera

ture

(°C

)

Time

Ocean Temperatures in Beaufort Gyre

200m depth

90m depth

Ice fraction

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Summary

Climate forcing reduces ice area primarily by surface melt

Halocline layer is very stable and does not warm

Large variations in heat transport in Beaufort Gyre break down Halocline insulation

Once broken the ocean heat flux removes remaining ice