Global warming is caused mostly by human activities. In the past, the temperature on earth more likely to be stable than now. Everything has changed since the industrial revolution. Every year, the levels of carbon dioxide constantly rise. Global warming occurs when carbon dioxide and other air pollutant and the greenhouse gases collect in the atmosphere and absorb the sunlight and solar radiation. In normally the solar radiation would escape into space, but the air pollutant and greenhouse gases in over the years, can trap the heat and causes the temperature in earth got hotter. It called by greenhouse effect.
In every country in among the world, burning the fossil fuel to make electricity is the largest source of heat trapping pollution. If we burning to much of fossil fuel, it will be too much carbon dioxide in our atmosphere. Besides the burning the renewable energy which is fossil fuel to make electricity, the secondary cause source of heat trapping pollution came from transportation sector, which generates about 1.7 billion tons of carbon dioxide emission.
The other causes of Greenhouses effect beside carbon dioxide are water vapor, nitrous oxide, methane, chlorofluorocarbons. The first example the causes greenhouse effect is water vapor. It is the most abundant greenhouse gas, but the water vapor had important effect which is can manage the climate. Water vapor can increase the heat of temperature in our earth, but water vapor also does have possibly of clouds and precipitations. It is the important feedback from water vapor.
 The other example of the causes greenhouse effect is chlorofluorocarbons which have a possibility to damaged our ozone layer. Synthetic compounds entirely of industrial origin used in a number of applications, but now largely regulated in production and release to the atmosphere by international agreement for their ability to contribute to destruction of the ozone layer. They are also greenhouse gases.