Burning natural gas isn't so awful but getting it out of the ground and to the place where is needs to be burned is always overlooked. It's a gas, it wants to escape and much of the infrastructure leaks and so a great deal is lost before its used. I walk around Boston and no joke you just SMELL it all the time because the infrastructure is so old. Natural gas is also mostly methane which when leaked is 80 times more potent than CO2. Furthermore much natural gas needs to be transported on ships to be uses. To summarize there is no 'greener' fossil fuels it's all to be avoided if possible.