A source of energy is considered nonrenewable if it cannot be easily replenished or regenerated in a short amount of time, often taking millions of years to form. Once these resources are used up, they cannot be replaced. Examples of nonrenewable energy sources include fossil fuels (coal, oil, and natural gas) and nuclear energy. Using nonrenewable energy sources can contribute to environmental degradation and climate change, as well as geopolitical instability due to competition for scarce resources.
