Most air pollution comes from burning fossil fuels. This can be reduced by making the combustion process more efficient, and by using various techniques to reduce the escape of harmful gases. This pollution is responsible for causing the earth to get warmer, called global warming. They are also non-renewable resources, there is only a limited amount of coal, gas, and oil, and it is not possible to make more. Eventually all the fossil fuels will be used. Some scientists think that coal will have run out by 2200 and oil by 2040. 