The life cycle of coal determines its carbon footprint. Its lifecycle is what determines whether or not it is a clean fossil fuel or a dirty fossil fuel. The exact same can be said for natural gas.

Each fossil fuel has a different life cycle. The extraction/production; refining/conditioning; transportation/storage; and combustion of each fossil fuel is different. And, each fossil fuel contributes greenhouse gases at different stages of its life cycle.

Likewise, at different stages, every fossil fuel contributes to global warming to a different degree.

For some fossil fuels, the extraction or production of some fossil fuels is the stage is the most polluting. It is during extraction that the largest sums of GHG escape into the atmosphere. For other fossil fuels, the greatest sum of greenhouse gas emission occurs during the combustion. During the life cycle of coal, for example, it is the combustion stage that is the most polluting.

Others produce emissions at every stage of the life cycle.

Life Cycle of Coal

The total environmental impact of coal is greater than any other fossil fuel. Especially with respect to open-pit coal mining, the environmental impact of coal cannot be overstated. From the destruction of forests, devastation of water quality, and the irreversible changing of landscape, coal mining has a massive impact on the environment.

With respect to carbon emissions, coal mining and the burning of coal account for a greater sum than any other fuel. Largely due to China’s exponentially greater dependence on coal than the rest of the world’s, coal mining and combustion leaves a larger carbon footprint than any other fossil fuel.

But, it is because coal is mined and burned in greater quantities than any other fossil fuel that it has the largest carbon footprint. Coal is not the dirtiest fossil fuel with respect to carbon emissions on a unit per measurement scale.

Per cubic meter, coal is not the dirtiest fossil fuel in terms of carbon emissions.

Carbon Emissions During Mining of Coal

Coal, unlike gas fuels and oil, does not emit carbons into the air in its natural state. However, during the mining of coal, methane is released into the air. Tremendous amounts of methane (CH₄) are released into the air in fact. Each year, in the U.S. alone, coal mining releases an estimated 61 million metric tons of carbon dioxide equivalent (MMTC02E) tons of methane into the air.

Methane as a Greenhouse Gas

Methane is a greenhouse gas with a carbon dioxide equivalent of 25. Carbon dioxide (CO₂)  is the standard for global warming potential. As such, its global warming potential rating is one (1). The difference between the two ratings is equivalent to 30 times. Methane is 30 times more potent as a heat-trapping carbon than CO₂.

Carbon Dioxide Emissions from Burning Coal

During storage and transportation, coal does not release greenhouse gases. Coal combustion, however, produces more greenhouse gases than the combustion of any other fossil fuel. There are a handful of coal types, but almost all contribute substantially more CO₂ into the air than other fossil fuels upon combustion.

Anthracite Coal emits 228.3 pounds of CO₂ per million Btu. Subbituminous Coal emits 214 pounds of CO₂ per million Btu. Burning a ton of Lignite Coal releases 215 pounds of CO₂ into the atmosphere. Bituminous Coal is the cleanest with respect to CO₂ emissions upon combustion, 205 pounds per million Btu.

Considering the sum of methane released into the air during the mining of coal and the CO₂ released upon combustion, it is easy to think of coal as the dirtiest fossil fuel.

However, coal is not the dirtiest fossil fuel with respect to global warming potential.

Lifecycle of Natural Gas

Lower than coal, diesel, gasoline, and propane, natural gas only emits 117 pounds of carbon dioxide per million Btu. However, natural gas does more to contribute to global warming than do coal, gasoline, and diesel. Far more in fact.

Methane is the reason natural gas does so much harm with respect to global warming. There are two reasons why. First, natural gas is methane. Conditioned natural gas is between 85 and 85 percent methane.

The second reason is that natural gas is a gas. That means it is extremely difficult to extract without large quantities escaping into the atmosphere. While oil drilling also releases methane into the atmosphere, the sum is not near that released during the drilling for natural gas. Oil wells release 23.3 MMT CO2 into the atmosphere. Natural gas wells release 172.6.

Coal is dirty because it releases large quantities of CO2 and methane into the air during its lifecycle. Natural gas, on the other hand, is dirty because it is natural gas.