What fossil fuel is the cleanest?

Quick Answers

Natural gas is often considered the cleanest fossil fuel when comparing carbon emissions. However, all fossil fuels produce significant greenhouse gas emissions that contribute to climate change. Some key points:

  • Natural gas produces 50-60% less carbon dioxide when burned compared to coal.
  • But natural gas production and infrastructure leads to methane leakage, another potent greenhouse gas.
  • Over a 20 year period, methane causes 86 times more global warming than CO2.
  • So methane leakage can significantly reduce the climate benefits of natural gas.
  • Per unit of energy, natural gas emits less air pollutants like NOx, SOx, particulates than coal and oil.
  • But even natural gas produces significant levels of harmful air pollution.
  • Renewable energy sources like solar, wind, geothermal are cleaner than any fossil fuel.
  • But natural gas is seen as a “bridge fuel” to transition from more polluting energy sources.

What are fossil fuels?

Fossil fuels are hydrocarbon deposits formed from the remains of ancient plants and animals that lived hundreds of millions of years ago. Over long time periods under intense heat and pressure, organic matter transformed into fuels like oil, natural gas, and coal. The three primary fossil fuels are:

  • Coal – Formed from decayed plant matter in bogs. Types include anthracite, bituminous, subbituminous, and lignite.
  • Oil – Formed from microscopic aquatic plants and animals. Found in underground reservoirs and extracted through wells and pumping.
  • Natural Gas – Formed alongside oil. Mainly comprised of methane. Often produced as a by-product of oil drilling.

These fossil fuel deposits are finite resources that take millions of years to form. But they now provide about 80% of the world’s energy needs, powering electricity generation, transportation, heating, manufacturing, and more. However, burning fossil fuels also generates significant carbon dioxide emissions that are the dominant cause of climate change.

Why are fossil fuels controversial?

While fossil fuels have powered economic growth over the past century, they also come with major drawbacks:

Climate change – Burning fossil fuels generates carbon dioxide, methane, and nitrous oxide emissions that trap heat and cause global warming and climate change. This threatens ecosystems, coastal cities, food and water supplies, and human health and security.

Air pollution – Fossil fuel combustion produces pollutants like particulate matter, nitrogen oxides, volatile organic compounds, and sulfur dioxide that reduce air quality and damage health. An estimated 4.2 million deaths annually link to air pollution.

Environmental damage – Oil spills can devastate marine ecosystems. Coal mining practices like mountaintop removal damage landscapes and pollute waterways. Fracking for oil and natural gas poses risks like groundwater contamination.

Public health – In addition to air pollution impacts, exposure to fossil fuel emissions increases risks of cancer, respiratory illness, and cardiovascular disease. The burning of coal still causes acid rain problems.

Finite resources – Fossil fuel deposits are nonrenewable. Their extraction, processing, and transportation require increasingly advanced technologies with higher economic and environmental costs.

How do fossil fuels produce emissions?

Fossil fuel emissions that drive climate change and air pollution come from two main sources:

Combustion Emissions

Burning fossil fuels releases gases and particles into the atmosphere. Key emissions include:

– Carbon dioxide (CO2) – The primary greenhouse gas, main driver of climate change.

– Methane (CH4) – More potent than CO2, also contributes significantly to warming.

– Nitrous oxide (N2O) – Long-lasting greenhouse gas.

– Particulates – Soot, ash, smoke, aerosols that harm health and add to smog.

– Sulfur oxides (SOx) – Lead to acid rain, lung irritation.

– Nitrogen oxides (NOx) – Ground level ozone and smog, respiratory impacts.

Extraction and Production Emissions

Producing, refining, and transporting fossil fuels also results in emissions, particularly:

– Methane leakage – Natural gas infrastructure allows methane, main component of natural gas, to escape into the atmosphere where it is a very potent greenhouse gas.

– Flaring – The burning of natural gas at the oil well site releases CO2, methane, and other hydrocarbons.

– Venting – Direct release of natural gas into the air during extraction. This is methane leakage.

– Spills – Accidental release of crude oil and petroleum products during storage and transportation causes air pollution through evaporation.

Reducing fossil fuel emissions will require transitions to renewable energy sources, electrification of transport and buildings, increased energy efficiency, and likely carbon capture on remaining conventional power plants.

How do emissions from different fossil fuels compare?

While all fossil fuels are major emissions sources, they differ in just how much greenhouse gases and air pollutants they generate relative to the energy they provide. Key comparisons:

Carbon Dioxide Emissions

Fossil Fuel CO2 Emitted (lbs/Billion Btu)
Coal (anthracite) 228.6
Coal (bituminous) 205.7
Coal (lignite) 215.4
Coal (subbituminous) 213.6
Diesel fuel and heating oil 161.3
Gasoline 157.2
Propane 139.0
Natural gas 117.0

– Coal has the highest CO2 emissions per unit of energy, followed by oil, and natural gas the lowest.

– Burning natural gas emits 50-60% less CO2 than burning coal.

Methane Emissions

Fossil Fuel Methane Emitted (lbs/Billion Btu)
Natural gas 2.3
Petroleum 0.3
Coal 0.9

– Natural gas infrastructure leads to substantially higher methane leakage rates.

– Methane is 86 times more potent than CO2 on a 20 year time scale.

Other Air Pollutants

Pollutant Natural Gas Oil Coal
Nitrogen Oxides (NOx) 0.092 0.448 0.457
Sulfur dioxide (SO2) 0.001 0.424 2.591
Particulates (PM) 0.007 0.084 2.744

– Natural gas combustion produces very low particulate matter, SO2, and NOx compared to oil and especially coal.

– These pollutants have negative health and environmental effects.

So while natural gas has lower carbon emissions at combustion per unit of energy compared to oil and coal, methane leakage throughout its lifecycle can significantly undermine that benefit. And all fossil fuels produce harmful air pollution to varying degrees.

Is natural gas actually cleaner?

Natural gas is often branded as the cleanest fossil fuel, providing a lower carbon “bridge” as the world transitions to renewable energy. But this reputation is being challenged due to methane leakage.

Climate Benefits of Natural Gas

– 50-60% lower CO2 emissions when burned compared to coal.

– Replacing coal with gas in electricity lowers power sector emissions.

– More flexibility than coal and nuclear, can better pair with renewables.

Concerns Around Methane Leakage

– Natural gas infrastructure leads to substantial methane leaks.

– Methane has 86 times the warming power of CO2 over 20 years.

– Just 3% leakage can negate climate benefits over coal.

– Estimates find 2-4% leakage across gas value chain.

Ways to Reduce Methane Impact

– Stricter regulations on leakage detection and repair.

– Improvements in valves, seals, pipelines to prevent leaks.

– Phasedown of oil and gas production to reduce extraction emissions.

– Shift to renewable energy sources like wind and solar.

While burning natural gas may produce fewer direct emissions than coal, managing leakage throughout the gas value chain is critical to maximize any climate benefits over other fossil fuels. Still, renewable energy remains the cleanest option.

How much air pollution comes from natural gas?

Compared to coal and oil, natural gas combustion does produce lower emissions of key air pollutants. But it still results in harmful levels of air pollution.

Nitrogen Oxides

– Contribute to smog, acid rain, and ground level ozone.
– Cause respiratory illness.
– Natural gas NOx emissions are 50% lower than coal.

Sulfur Dioxide

– Major cause of acid rain.
– Leads to haze and particulate formation.
– Natural gas SO2 emissions are 99% lower than coal.

Particulate Matter

– Soot, smoke, ash that causes respiratory issues.
– Natural gas particulate emissions are 99% lower than coal.

Volatile Organic Compounds

– Contribute to smog formation and ground level ozone.
– Linked to cancer and organ damage.
– Emitted from incomplete combustion and methane leakage.

While natural gas has lower emissions for these major pollutants, it is not emission free. Stricter regulations, efficiency improvements, pollution controls, and transitions to renewables are still needed to improve air quality.

Why consider natural gas a “bridge” fuel?

Natural gas is often described as a “bridge fuel” – an energy source that is not as clean as renewables but cleaner than coal and oil as we transition to low-carbon energy systems. There are several key advantages to natural gas:

Lower Carbon Intensity

– 50-60% lower CO2 per unit of energy when burned compared to coal.
– With methane leakage controlled, can reduce overall GHG emissions from power sector.

Cleaner than Coal and Oil

– 99% lower sulfur dioxide emissions than coal and oil.
– Far fewer particulates than from burning coal.
– Can help reduce air pollution when displacing other fossil fuels.


– Rapid ramping capability supports growth of variable renewables like wind/solar.
– Dispatchable baseload power to complement intermittent sources.

Existing Infrastructure

– Large natural gas pipeline network and power plants already in place.
– Lower barriers than building whole new energy systems.

Cheap and Abundant Supply

– Fracking boom has created large surplus of low-cost gas.
– Can keep energy costs lower as renewable supplies increase.

But methane leakage risks, remaining air pollution, and need to transition fully to carbon neutral call into question how long natural gas can serve as an effective bridge and what role it should play.

How does natural gas compare to renewable energy?

Natural gas has some advantages over coal and oil, but renewable energy sources like solar, wind, geothermal remain far cleaner options with zero direct emissions.

Greenhouse Gas Emissions

– Renewables – Zero direct GHG emissions during operation.

– Natural Gas – Lowest emitting fossil fuel when methane leakage controlled, but still significant CO2 and methane emissions.

Air Pollution

– Renewables – Negligible air pollutants emitted during operation.

– Natural Gas – Low SO2, NOx, particulates compared to coal but still emits at harmful levels.

Health and Environmental Impacts

– Renewables – Minimal negative health and ecological impacts.

– Natural Gas – Contributes to respiratory illness, smog, acid rain. Risks from fracking, methane leakage.


– Renewables – Vast solar, wind, geothermal resources can expand to meet all energy needs.

– Natural Gas – Remaining reserves likely inadequate to displace all coal/oil long-term as supplies deplete.


– Renewables – Plummeting costs, now cheaper than coal and gas for electricity generation.

– Natural Gas – Cheap due to fracking boom, but higher long-term economic costs from climate and health damages.

While natural gas emits less than coal and oil, renewables represent the cleanest, lowest impact energy option with the greatest scalability to sustainably meet future energy demand.


Natural gas is the lowest carbon emitting fossil fuel and can provide a cleaner alternative to coal and oil, but it is not without significant disadvantages when it comes to greenhouse gas emissions and air pollution. While natural gas emits 50-60% less CO2 than coal when burned, methane leakage throughout the production and distribution process can greatly reduce its climate advantage unless strictly controlled through regulations and technologies. Natural gas also creates less air pollution than other fossil fuels, but still produces harmful levels of nitrogen oxides, volatile organic compounds, and particulate matter. And it still relies on the extraction of finite resources. Renewable sources like wind, solar and geothermal are cleaner across the board, with near zero emissions and far lower health and environmental impacts. Natural gas does offer some advantages as a “bridge fuel” over the short term, but minimizing leakage, continuing to improve efficiency, implementing pollution controls, and increasing renewables will be critical to maximize any climate and air benefits.

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