Fossil fuels are finite, and once the last well has dried up, that's it. As the industrialized economy grows, making higher demands on the energy supply, so the earth's fuel reserves are depleted. The consequences of this are energy poverty and economic stagnation if other types of energy aren't adopted.
Nuclear energy produces nuclear waste that has to be disposed of in a way that does not harm the environment or the public. While practices have improved over the last 20 years, disposal standards were a lot less strict at the beginning of the atomic age.
The risk of leaks and meltdowns are real. In 1986, the nuclear power plant in Chernobyl suffered a partial meltdown in reactor 4, sending a plume of radioactive materials into the atmosphere. The radioactivity was carried west across Europe as far as Great Britain. Over 200 villages and hamlets in the greater Belorussian area were hastily evacuated. Higher cases of childhood thyroid cancer have been reported in the former Eastern Bloc.
The 2011 explosion at the Fukushima plant in Japan reminds us of the dangers of nuclear energy.
Burning fossil fuels produces sulfur dioxide, causing acid rain and carbon monoxide, which contribute significantly to global warming. Rising sea temperatures are likely to make hurricanes more intense. Migratory birds are spending their winters farther north and as the polar ice caps melt, sea levels will rise. The United States is projected to lose 10,000 square miles of coastal land by the end of the 21st century.
Renewable energy comes from wind, waves and the sun, and harnesses the natural energy flows of the planet. Each type has technical challenges that scientists are working to overcome. Moreover, each requires massive investment to raise production to a level that will satisfy current and future energy demands. The alternatives are clean, abundant and do not contribute to global warming or the destruction of the environment.