When coal came into the picture, it took about 50 or 60 years to displace timber. Then, crude oil was found, and it took 60, 70 years, and then natural gas. So it takes 100 years or more for some new breakthrough in energy to become the dominant source. Most people have difficulty coming to grips with the sheer enormity of energy consumption.
Natural gas obviously brings with it a number of quality-of-life environmental benefits because it is a relatively clean-burning fuel. It has a CO2 footprint, but it has no particulates. It has none of the other emissions elements that are of concern to public health that other forms of power-generation fuels do have: coal, fuel oil, others.