Global warming is driven by the greenhouse effect. It's not actually all bad: without it the Earth would be a much colder place! However, you can have too much of a good thing.
The greenhouse effect is the name given to the trapping of heat in the earth's atmosphere, mainly due to carbon dioxide (CO2) gas.
Human activities, such as the burning of fossil fuels, are increasing the concentrations of CO2 in the air. Using renewable energy sources will help to reduce the effects of climate change.