Surface Albedo

Aluminium foil 90

Dry concrete 1 7-35

Black bitumen 10

Red clay tiles 30

New galvanised iron 45

Rusty iron 10

Thatched roof 15-20 Window negligible

Fresh white paint 75

Red, brown or green paint 30

Clean white car 54

Dirty black car 10

Caucasian human skin 40

Negro skin 18

Snow 80*

Wet soil 10

Dry sand, desert 40

Rainforest 13

Eucalypt forest 18

Pine forest 13

Grassland, green vegetation 22

Water with Sun above 3.5

Water, Sun at 45° elevation 6

* See Linacre (1992:307) for more details the albedo of water is usually taken as about 6 per cent overall.

This is far less than the albedo of ice, i.e. about 50 per cent in the case of sea-ice and 80 per cent for fresh snow. So the extent of sea-ice around Antarctica governs how much solar radiation is absorbed and hence global temperatures (Note 2.J). The high albedo of fresh snow almost doubles the solar radiation onto the faces of skiers, which can lead to sunburn, even under the chin.

The albedo of clouds is less when the density is low or the droplet size large (Table 2.4). A typical figure for thin cloud like cirrus (Chapter 8) is 35 per cent and for cumulus 85 per cent. The high figures help explain why so little solar

Plate 2.1 The low albedo of the beach at Kusamba in Bali means that almost all the incoming solar radiation is absorbed and can be used to evaporate moisture from the sand, which makes it practicable to extract salt from the sea. The beach's unusual blackness is due to the volcanic eruption of nearby Mt Agung in 1963, showering dark-coloured rock and dust over a wide area. The photograph shows small subdivisions of the beach, each fronting the sea. A man scoops sea water into large buckets and carries it up onto his patch in the morning and then waits for it to dry in the sunshine, leaving a salty surface layer of sand. This is subsequently scraped off and carried into a hut, where the salt is rinsed out as a concentrated solution, which is then completely dried in wooden troughs discernible further inland.

radiation is absorbed by cloud, and therefore why cloud is not readily evaporated away.

The planetary albedo is the reflection of solar radiation from the entire globe, as a fraction of the extra-terrestrial radiation. It is about 30 per cent for the Earth as a whole. This is much more than the albedo of the Moon, which has neither clouds nor polar ice: the value there is only about 7 per cent. So the Earth appears about four times brighter than the Moon when viewed from space.

The variation of the planetary albedo with latitude is shown in Figure 2.15. The slight maximum at the equator is due to the cloudiness there. High values at the poles result from cloudiness, the covering of ice and snow, and the dependence of albedo on solar angle,

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