Our earth retains its temperature thanks to a layer of "greenhouse" gases in the atmosphere, which trap energy from the sun. Without this layer of gases, the average global temperature would be more than 30°C colder than it is now.
As human activities involving the burning of fossil fuels increase, the concentrations of greenhouse gases, particularly Carbon Dioxide (CO2), build up in the atmosphere. This causes the world to heat up unnaturally, the weather to become more unpredictable, and increases the likelihood of more extreme weather events. This heating process is often referred to as global warming and the overall effect is known as climate change.
We all contribute in some way towards increasing the layer of gases. We do this by using energy. Energy used directly, such as transport, heating or cooling our homes and workplaces, cooking food or any other use, such as lighting. We also contribute indirectly through the energy that goes into producing all the things we purchase, from necessities like food, water, houses, clothing or healthcare, through to non-essentials like DVD's, cosmetics or holidays.