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 Effects
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 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 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.
Because there are more and more greenhouse gases in the atmosphere, more heat is trapped which makes the Earth warmer. This is known as GLOBAL WARMING.
A lot of scientists agree that man's activities are making the natural greenhouse effect stronger. If we carry on polluting the atmosphere with greenhouse gases, it will have very dangerous effects on the Earth.
With more heat trapped on Earth, the planet will become warmer, which means the weather all over Earth will change. For example, summers will get hotter, and winters too. This may seem a good idea, but the conditions we are living in are perfect for life, and a large rise in temperature could be terrible for us and for any other living thing on Earth.
At the moment, it is difficult for scientists to say how big the changes will be and where the worse effects will occur.
In Britain, winter and summer temperatures will increase and the weather will be warmer. In winter it may also rain more but in summer it may become drier.
In other parts of the world, the effects will be different, some places will become drier and others will be wetter. Although most areas will be warmer, some areas will become cooler. There may be many storms, floods and drought, but we do not know which areas of the world will be affected.
All over the world, these weather changes will affect the kind of crop that can be grown. Plants, animals and even people may find it difficult to survive in different conditions.
For example, between 1901 and 2012, it is believed that the earth's temperature has risen by 0.89 °C. Rainfall amounts have also risen in the mid-latitudes of the northern hemisphere since the beginning of the 20th Century. It is also believed that sea levels have risen up to about 19cm globally, with lots of glaciers melting in addition.
Higher temperatures will make the water of the seas and oceans expand. Ice melting in the Antarctic and Greenland will flow into the sea. All over the world, sea levels may rise, perhaps by as much as 20 to 40 cm, by the beginning of the next century.
Higher sea levels will threaten the low-lying coastal areas of the world, such as the Netherlands and Bangladesh.