Ice with everything - Antarctica: Global Science from a Frozen Continent - page 74

Box 3.1 Albedos of different types of snow and ice surfaces

The albedo (from the Latin word ' albus ' , white) or re ectivity of a surface

is a measurement of its ef ciency in re ecting sunlight. Albedo is de ned as

the ratio of diffusely re ected to incident radiation.

The albedo of growing sea ice depends on its thickness, increasing strongly
from values of 10% for 0 5 cm shallow sea ice to 35% for 30 cm thick sea ice. It

also increases when sea ice cover breaks into small pieces. The presence of a thin
layer of snow (a few centimetres) can also completely change the albedo,
reaching values above 80% for dry and fresh snow.
The albedo of sea ice is one of the well-known positive feedbacks associated
with climate change. In response to an initial change, a temperature increase can
result in sea ice melting. The disappearance of sea ice, in turn, reduces the surface
albedo and increases the absorption of sunlight, which increases the surface
warming and the melting of the ice.
The albedo feedback is one of the mechanisms involved in the polar
ampli

-

cation of climate change, together with dynamic changes in atmospheric
circulation, water vapour and cloud feedbacks.

Figure 3.7 Albedos of basic thick

sea ice surface types. (Credit: UNEP
Global outlook for snow and ice)

Albedo
(% of radiation reflected)
100

Dry
snow

80

Wet
snow

Bare ice

60

New melt
pond

40

Mature
melt
pond

20

Open
water

0