Nonrenewable Energy

• Resources such as coal, oil and uranium exist on Earth in finite quantities. Coal deposits form when dead plant material is buried and compressed over millions of years. Most coal formed from plants alive in swamps during the Carboniferous Period. Oil forms similarly, with ocean life dying, sinking to the sea floor and being buried and compressed over millions of years. Radioactive deposits like uranium formed along with the planet itself. Society burns coal and oil and splits radioactive elements, to generate heat and electricity. Once the combustion or radioactive decay is complete, the resource is consumed and cannot be reused. Eventually, there will come a point in history when humanity depletes these nonrenewable resources.
  
  

Renewable Energy

• Society today uses two renewable resources, wood and water, to meet certain energy needs. Both constantly replenish themselves through natural cycles. The potential exists to degrade these resources' renewable characteristics. Forests decline when lumber is harvested faster than it is regenerated. If overharvesting happens too intensely or for too long, the forest is destroyed and cannot regenerate itself. Water, too, can be misused. A river with large dams and numerous points of diversion for agricultural or residential use has its downstream volume reduced significantly or eliminated, so the river no longer reaches its natural destination. Mismanagement of renewable energy sources is often reversible, provided there is something left to salvage.
  
  

Perpetual Energy

• As long as the sun shines, perpetual energy sources will be available on Earth. Solar and wind energy cannot be diminished or degraded in any way. Photovoltaic cells and solar-thermal power plants capture energy directly from sunlight and convert it to electricity. Wind comes from the uneven heating of Earth's surface by the sun. This uneven heating produces pressure gradients in the atmosphere, which creates wind as the air tries to move around to even itself out. Wind turbines capture this energy to generate electricity.
  
  

Humanity's Future Energy Use

• The United States, with vast coal deposits and heavy oil imports, relies primarily on nonrenewable resources. The use of perpetual sources continues to increase, however, as the cost of nonrenewable sources increases. Other countries, like Denmark, continue to transition away from nonrenewable energy toward renewable and perpetual energy. At the time of publication, Denmark generates approximately 20 percent of its energy needs from wind.