Alternative energy refers to any form of energy that is derived from sources other than traditional fossil fuels such as coal, oil and natural gas. This includes renewable forms of energy like solar power, wind power, hydroelectricity, geothermal energy, biomass and biofuels among others. The term "alternative" refers to the fact that these sources are an alternative to non-renewable fossil fuels which contribute significantly to greenhouse gas emissions and climate change. Alternative energy is often used as a way to reduce dependence on finite resources, decrease pollution and greenhouse gases, promote sustainability and support long term energy security.