What are the two major concerns over using fossil fuels for energy?

The future availability of fossil fuels as our demand increases is certainly an issue that is of major concern.

The environment is another issue. The spilling of oil into open waters or on land can be very bad for the local environment.

A:The major concern over using fossil fuels for energy is the carbon dioxide, a powerful greenhouse gas, which is released whenever coal, oil or natural gas are burned. This extra carbon dioxide adds to the greenhouse gases in the atmosphere and is causing global warming.

All other concerns pale in comparison.