Coal, oil, and natural gas all formed hundreds of millions of years ago from the organic remains of ancient plants and animals. Today, fossil fuels are the largest source of energy worldwide and are important natural resources. Fossil fuels are nonrenewable resources, so their use must be conserved in order for the supply to last. Harvesting and burning fossil fuels creates a wide variety of negative environmental effects like air and surface pollution, water pollution, human health risks, and global climate change.