The Earth is wrapped in a blanket of air called the 'atmosphere', which is made up of several layers of gases. The sun is much hotter than the Earth and it gives off rays of heat (radiation) that travel through the atmosphere and reach the Earth. The rays of the sun warm the Earth, and heat from the Earth then travels back into the atmosphere. The gases in the atmosphere stop some of the heat from escaping into space. These gases are called greenhouse gases and the natural process between the sun, the atmosphere and the Earth is called the 'Greenhouse Effect', because it works the same way as a greenhouse. The windows of a greenhouse play the same role as the gases in the atmosphere, keeping some of the heat inside the greenhouse.
THE NATURAL GREENHOUSE EFFECT
The atmosphere has a number of gases, often in tiny amounts, which trap the heat given out by the Earth.
To make sure that the Earth's temperature remains constant, the balance of these gases in the atmosphere must not be upset.
The GREENHOUSE GASES are very important and are mainly:
water vapour
occurs naturally in the atmosphere.
carbon dioxide
produced naturally when people and animals breathe. Plants and trees absorb carbon dioxide to live. Volcanoes also produce this gas. Carbon dioxide is not the same as carbon monoxide (See Air Quality)
methane
comes from cattle as they digest their food. The gas also comes from fields where rice is grown in paddy fields.
nitrous oxide
when plants die and rot, nitrous oxide is produced.
ozone
occurs naturally in the atmosphere.
THE ENHANCED GREENHOUSE EFFECT
Some of the activities of man also produce greenhouse gases. These gases keep increasing in the atmosphere. The balance of the greenhouse gases changes and this has effects on the whole of the planet.
Burning fossil fuels - coal, oil and natural gas - releases carbon dioxide into the atmosphere. Cutting down and burning trees also produces a lot of carbon dioxide.
A group of greenhouse gases called the chlorofluorocarbons, - which are usually called CFCs, because the other word is much too long! - have been used in aerosols, such as hairspray cans, fridges and in making foam plastics. They are found in small amounts in the atmosphere. They are dangerous greenhouse gases because small amounts can trap large amounts of heat.