The world's supply of oil is finite. Natural gas burns cleanly but is in limited supply and also produces some CO2. Nuclear power causes little air pollution, but hazards exist for accidents and disposal of nuclear waste. Hydroelectric, wind, geothermal, and solar energy sources remain limited to specialized geographic regions and are relatively minor suppliers in the overall energy picture. An energy shortfall could occur as early as the mid-21 century as demand for energy far outstrips supply.
Fossil fuel is also environmentally costly.
64 Ibs of CO2 is produced per American per day from fossil fuel usage. Fortunately, a new energy source is presently being developed which can provide an abundant source of future energy. All life on earth is directly or indirectly dependent on the fusion energy of the sun. To understand fusion, it is necessary to compare it to what it is not-which is fission. In nuclear fission, a heavy atom such as uranium is split, which releases energy.