Energy and the Environment

Energy from the Sun

The conditions which support life on earth are determined by a finely balanced system of energy transfer - from the Sun to the planet's surface, and from the planet's surface back towards space.

The Sun is the Earth's only external source of heat. Energy in the form of radiation travels towards the Earth. Some of it is reflected back into space by the atmosphere, some of it is absorbed by the atmosphere, and some passes through to warm the planet's surface.

The warmed Earth transmits energy back towards space in the form of infra-red radiation. But something happens to keep our planet warm. A number of gases in the atmosphere act as a blanket, trapping some of the infra-red radiation and preventing it escaping to space. (This is similar to the principle of a greenhouse, in which the glass allows sunlight through but traps the infra-red radiation, thus causing the inside of the greenhouse to warm up).

If the Earth had no atmosphere, all of this radiation would escape and the planet would be as cold as the surface of the moon - below freezing point. On the other hand, if the Earth had an atmosphere like the planet Venus, which is almost entirely carbon dioxide (CO₂), too much heat would be trapped and life as we know it could not exist. The surface temperature of Venus is estimated to be about 477°C, though the Earth would be unlikely to get that hot, as it is further from the Sun.

The conditions for life depend on the Earth having the right balance of greenhouse gases in the atmosphere. One of the most important greenhouse gases - water vapour - occurs naturally as a consequence of the water cycle. Water is constantly evaporating from the land and seas and falling to Earth again as precipitation (rain, snow or hail).

However, many of the greenhouse gases not only occur naturally in the atmosphere but are also produced artificially.

One example is carbon dioxide - CO₂.

Since the Industrial Revolution in the 1700s, human activities, such as the burning of oil, coal and gas, and deforestation, have increased CO₂ concentrations in the atmosphere.

In 2006, global atmospheric concentrations of CO₂ were 36% higher than they were before the Industrial Revolution.¹ Almost all of the increase is due to human activities. Present CO₂ concentrations are higher than any time in at least the last 650,000 years.²

The Greenhouse Effect

The process began with the Industrial Revolution, when more fuel was burned to power new machinery. Today CO₂ is being added to the atmosphere by industry, by transport and by the conventional methods of generating electricity. Could this lead to a runaway Greenhouse Effect?

The eventual effect of the enhanced Greenhouse Effect is still being discussed by scientists. Their investigations have led to suggestions that the Earth's temperature could rise by between 2°C and 5°C. This could in turn lead to a rise in sea levels through the expansion of the oceans and the melting of glaciers and polar ice. Again, the predictions vary, but rises of between 20 and 30 centimetres have been suggested. This could lead to extensive flooding of low-lying coastal areas throughout the world.

Other consequences of the Greenhouse Effect could be a change in the distribution of vegetation, with some areas becoming more suitable for agriculture, while others become less fertile.