The Greenhouse Effect

There are a number of gases responsible for pollution and other changes in air quality.  However there is one main gas that is causing important changes in the Earth’s weather, and this is again released into the atmosphere by humans. This gas is carbon dioxide (CO₂).

Although CO₂ exists naturally in the atmosphere, its concentration is being significantly increased by man’s activities. When something is burned – either fossil fuels in power stations or trees in the rainforests, for example - CO₂ is released. Each year, areas of tropical forest the size of Iceland are destroyed to create temporary pasture for cattle, mainly in the Amazon Basin in Brazil. This has a double impact on the amount of CO₂ in the air, as trees naturally absorb excess CO₂ from the air as they grow. So when there are less of them, a smaller amount of CO₂ is removed – and when they are burned, even more is added.

Carbon dioxide has been termed a "greenhouse gas" because of the role it plays in regulating the Earth’s climate. It acts like the glass in a greenhouse, trapping heat and keeping the Earth at a comfortable temperature. In fact, greenhouse gases are beneficial in small quantities, and without them the temperature on Earth would be too low to sustain life. However, as their quantities increase, they trap more heat and the Earth becomes warmer. This artificial warming has been termed "the greenhouse effect", and it could have considerable consequences for the climate of the Earth as a whole. If the Earth warms up by just a few degrees, the polar ice caps could melt and higher sea levels would flood low-lying areas, including important cities such as London, New York and Sydney.

However, the greenhouse effect is not the only threat to the world’s weather and climate caused by humans.  The ozone hole is another one, and this will be studied in more detail on the next page.