METEOROLOGISTS worry a lot about their albedo. Lest there be any confusion on the matter, this is quite different from the Freudian concept of the libido, whose meteorological connections were so aptly summed up by Lord Byron, when he wrote in Don Juan:
What men call gallantry, and gods adultery,
Is much more common where the climate's sultry.
As far as I am aware, no major studies have been carried out on the meteorological libido, but the albedo - the reflective power of Planet Earth - is a topic of constant interest: any change would have serious consequences for the global climate.
Radiation from the sun, directly or indirectly, is the sole source of fuel for the earth's weather machine. The destructive force of the hurricane, the power of the waves against the sea shore, and the warmth of a southerly breeze - they are all manifestations of solar energy in as many different guises.
But not all the sun's energy beamed in our direction is available for use in this way: a significant proportion of it is reflected back to space rather than being absorbed by the earth atmosphere system, and the fraction so affected is known as the Earth's albedo.
The word comes from the Latin albus, meaning "white" - a reference to the high reflecting power of a white surface.
The albedo varies from place to place depending on the texture of the surface, the local composition of the atmosphere, or the elevation of the sun.
Fresh snow, for example, reflects up to 90 per cent of any solar radiation reaching it. Clouds, too, reflect 70 or 80 per cent of the sun's energy, while green fields reflect only about 20 per cent.
Water, strangely enough, reflects very little - only 4 or 5 per cent - unless the sun is very near the horizon, in which case reflection is almost total.
With normal amounts of cloud, snow and vegetation, the total albedo of the earth atmosphere system is estimated to be around 40 per cent. In other words, two fifths of the sun's incident energy is reflected back into space, while the remaining three fifths is absorbed by the planet and its surrounding layers of air.
These proportions are critical to the stability of the earth's climate. The areas around the North and South Poles, for example, are covered by ice and snow, and absorb very little solar energy at present.
But if circumstances were to change so that there was less ice and more greenery in the polar regions, more energy would be absorbed, and there would be a gradual rise in global temperature.