SQA Higher Geography

## Energy from the sun Almost all the energy that drives the atmosphere and the oceans arrives from the sun as short-wave radiation, called **insolation** (incoming solar radiation). The Earth sends energy back to space as long-wave (infrared) terrestrial radiation. Over a long period the two are in balance, so the planet does not keep getting hotter or colder, and the balance is called the **global heat budget** or global energy budget. The budget has to balance for the planet as a whole, but not at every place on it. Some latitudes receive more energy than they lose and others lose more than they receive, and the movement of air and water between them is what makes weather and climate. ## What happens to insolation Of the radiation that reaches the top of the atmosphere, roughly 30 per cent never warms anything. It is reflected straight back to space by clouds, by dust and gas molecules in the air and by bright surfaces such as ice and snow. Roughly 20 per cent is absorbed by the atmosphere itself, mostly by water vapour, ozone, carbon dioxide and clouds, and roughly half passes through and is absorbed by the land and the oceans. These proportions are approximate and vary from one estimate to another, but the pattern does not: the surface receives about half of the insolation, and the atmosphere is mainly warmed from below. The warmed surface then does three things with the energy: - it radiates long-wave energy upwards, and much of this is absorbed by greenhouse gases…