Because fossil fuel reserves are shrinking and their use is tied to global environmental changes, most experts insist on the need for alternative renewable energy sources, including some of the sources mentioned in this video segment. Unfortunately, no perfect alternative has been identified. Each comes with its own set of problems.

For example, although the sun offers an almost limitless supply of energy, solar panels are expensive to produce, take up a lot of space, and convert only 15 percent of the energy they capture into usable electricity. They also produce power only during cloudless days. Windmills capture another seemingly infinite energy source. But they too produce electricity inconsistently. Other energy alternatives, including nuclear fusion and hydrogen power, hold promise for the future. At present, however, the energy cost of processing them or driving their reactions are as high as the energy they produce.

Today, engineers are working both to improve existing technologies and to develop new technologies in an effort to overcome the shortcomings associated with energy alternatives. They are working to develop solar panels that are less expensive to manufacture and more efficient at converting sunlight into electricity. Some engineers and scientists suggest that launching solar satellites into space, where they can collect sunlight 24 hours a day and beam this energy back to Earth, may be the answer. Others are mapping the world's windiest locations in order to maximize the return from future wind farms.

Even with so many alternative energy sources on the horizon, many experts insist that we may be fast approaching an energy crisis. Some predict that accessible fossil fuels will be depleted in as few as 40 years, unless the world moves quickly to reduce energy consumption. By reducing consumption we can both extend the life of the non-renewable energy sources we have now, and make the use of renewable alternatives more feasible.