The Sea Ice-Albedo Feedback in a Warming Climate: Albedos from Today

and Reflections on Tomorrow

Don Perovich1 and Tom Grenfell21Cold Regions Research and Engineering Laboratory, 2University of Washington

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incident

reflectedAlbedo

Melting

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Lower albedoAbsorbedsunlight

Ice-albedo feedback: seasonal evolution

July August 7 September

April May 17 June 10

Surface types: snow, bare ice, melt ponds, and leads

Albedo evolution of surface types

Snow, leads, bare ice constant – ponds always changing

Surface physical propertiesJune 17 August 7

Regenerating surface scattering layer Deepening ponds

• Estimate as a composite of surface types• determine the albedos of types• determine the relative areas (A)• albedo () is linear combination

•S=snow, i=, p=pond and w=water.

wwppiiss AAAA

Large-scale albedo

Combine albedos with fractional areas

Albedo evolution

5 phases – timing is critical

Snow warming

Pond evolution

Fall freezeup

Pon

d fo

rmat

ion

Sno

w m

elt

General form

Know form of albedo evolution

Modest changes

Adjust “wavelength” and “amplitude”

What if …Multiyear

Not a minor adjustment – it’s a new regime

First year

big changes

First year ice – albedo evolution

Decrease is rapid

First year ice – albedo evolution

Decrease is rapid, sometimes is reversed

First year ice – albedo evolution

Decrease is rapid, sometimes is reversed, sometimes oscillates

First year ice – albedo evolution

24 June

15 June

18 June

• Tremendous variability• Multiple evolutionary paths

• Flooded• Drained• Superposed

• Need to understand physical properties• Role of melt, topography, and permeability

Big change in physical evolution – big change in albedo evolution

Deformed first year ice

Who knows? Interconnections cause cascading changes

Changes are happening now

Average bottom ablation from 100 thickness gauges

Bottom ablation measured at SHEBA - 1998

Bottom ablation and solar heating

In the past source of heat was sunlight deposited in leads

SHEBA 1998Heat used in bottom ablation

Solar heating

Transmittance through leads not sufficient

Solar heating

Leads, melt ponds and bare ice all contribute

1975 versus 1998

Ice is thinner, transmission to ocean is greater

• No change in bare ice albedo• Decrease in pond albedo• Increase in bare ice transmittance• Major increase in pond transmittance

• Simple optical model• “Standard” ice conditions

• 3.0 m vs. 1.5 m• 2.5 m vs. 1.0 m

Summary

Integration and synthesis are key

Current state•Good understanding•Five distinct phases in albedo evolution•Summer is the interesting time•Melt ponds are major uncertainty

Modest changes•Fundamentals are the same•Can adapt present treatment•Change “wavelength / amplitude” of albedo cycle

Major changes•All bets are off•Can speculate, but not extrapolate•Probably accelerated feedback•Difficulty is that changes are interrelated