Global warming refers to the increase in average temperature near the earth's surface and in its oceans. Climate change is another term used interchangeably with global warming. However, climate change may encompass other changes in climate besides increases in temperature.

In the past century the average air temperature near the earth's surface has increased by around 1.4 degrees Fahrenheit. Various models have attempted to predict how these temperature changes may impact on the future. They variously predict increases from 2.5 to 10.4 degrees Fahrenheit. Most scientists agree that temperatures are likely to continue increasing. However, they do not agree nearly as much when it comes to predicting the magnitude of the increase.

So what actually causes the increased temperatures?

The earth's temperature is affected by many factors such as:

The earth's orbit - The tilt of the earth axis as it revolves around the sun influences the amount of sunlight reaching earth. Therefore changes in the earth's orbit affects its surface temperature.

Changes in intensity of heat emitted by the sun can also affect temperature on earth.

Volcanic activity - Lava, ash, dust and hot gases from volcanic eruptions can create volcanic aerosols which reflect heat away from the earth's surface and result in cooler temperatures. For instance 1816 is said to have been a year without a summer - widely believed to have been a result of the eruption of the Tambora volcano in Indonesia in the previous year. On the other hand, volcanoes also emit huge quantities of Carbon Dioxide, which tend to have the opposite effect and could lead to higher temperatures.

The causes listed above have existed for a very long time. However, since the Industrial Revolution and especially since 1900 another cause has taken precedence. Increased use of fossil fuels and the resulting emissions of carbon dioxide have caused massive increases in greenhouse gases. This has led to increased temperatures through the greenhouse effect.

What is the greenhouse effect and how does it impact on surface temperature?

The earth receives heat from the sun. The earth loses heat by reflecting it back into the atmosphere. The atmosphere contains a mixture of gases that trap heat and keep the earth's surface warm. This is similar to the mechanism that keeps the inside of a garden greenhouse warmer than the outside. These greenhouse gases are vital for life on earth.

If they did not exist it is likely that earth would be too cold to sustain life. However, too much of a good thing can have bad consequences. As a result of our energy intensive lifestyles and the burning of vast quantities of fossil fuels the levels of greenhouse gases have been increasing rapidly which magnifies the greenhouse effect and traps more and more heat close to the earth's surface. Greenhouse gases are primarily Water vapor, Carbon Dioxide, Methane, Nitrous Oxide and Ozone.