Combustion of both, natural gases or coal, generates electricity, but natural gas combustion has a smaller environmental impact than the combustion of coal or oils.
First of all, the amounts of dangerous air emmisions, such that carbon dioxide or nitrogen oxide, are lower in case of combustion of natural gas in comparison with combustion of coal.
The amounts of water resources are reduced in the combustion of natural gases, however, the combined cycle process of combustion needs water for cooling, thus, in this case, aquatic life can be affected.
The water discharges are not necessary in case of combustion of natural gases, but there exists cases when the heat and pollutants in gas boilers request a water discharge.
Hence, analyzing the environmental impacts produced by both methods of producing energy, either burning natural gas or coal, yields that both can affect the environment by destroying the plants and natural habitat for animals, by contaminating the sites with various pollutants, though, the natural gas combustion seems to produce less injuries to environment, than coal or oil combustion.