Climate can be best understood if it is described as "expected weather." It is, in essence, the long-term statistical expression of short-term weather. When there are changes in the expected weather, we say the climate has changed. They can be defined by the differences between average weather conditions at two separate times. A change in climate is possible in different ways, over different time scales and at different geographical scales. In recent times, scientists are busy exploring global warming, due to mankind's impact on the climate system, through the enhancement of the natural greenhouse effect.
The global climate is largely determined by the global energy balance, especially the balance between energy the earth receives from the sun and the energy which the earth releases back to space. Climate change can take place on account of any process that can change the global energy balance, and the energy flows within the climate system. There are several causes of climate change, including changes in the earth's orbit around the sun, changes in the amount of energy coming from the sun, changes in ocean circulation or changes in the composition of the atmosphere. Huge volcanic eruptions and the movement of continents around the world over millions and millions of years also cause climate change over different time scales.
In the midst of these natural causes of climate change, one man-made factor is perhaps the most well-known. It is the pollution of the air that may be contributing to global warming. The greenhouse gases present in air trap heat in the atmosphere and keep the earth warmer than it should be, and suitable for life. This is called the natural greenhouse effect. In the last 200 years or so, mankind has increased the amount of greenhouse gases in the atmosphere by burning fossil fuels like coal, oil and gas. As a result of this, more heat is being trapped in the atmosphere leading to a change in the climate of the earth.
Since the beginning of the 20th century the temperature of the earth has gone up by more than 0.5°C. Although this may not sound too alarming for real concern, the fact is that during the last Ice Age, the earth was on average only 5°C colder than today. And unless we take enough precautionary measures to reduce air pollution, the phenomenon is likely to continue in the 21st century as well. And research studies suggest that the earth may be warmer by another 2 or 3°C by 2100.
The amount of greenhouse gases in the atmosphere has increased in the recent past mainly due to burning of fossil fuels for energy and transportation, and land use changes, for food by mankind. It is now widely believed that global warming is the consequence of increases in greenhouse gas emissions for which we are to blame ourselves. While other natural causes of climate change, such as changes in the amount of energy coming from the sun and shifting patterns of ocean circulation can cause global climate to change, global warming has brought to notice clear signs of human influence on the global climate.
