Comparing Liquefied Natural Gas with coal is one of the most-repeated questions in energy debate. The honest answer is that LNG is generally better than coal on most environmental axes — sometimes by a large margin — but the size of the advantage depends heavily on methane leakage along the gas chain. Getting the comparison right requires being specific about what is measured, where, and over what timescale.
At combustion: gas is clearly cleaner than coal
On a per-unit-of-energy basis at the burner tip, natural gas emits substantially less CO₂ than coal:
- Natural gas combustion emits approximately 53 kg CO₂ per MMBtu (roughly 0.41 t CO₂/MWh-thermal).
- Bituminous coal combustion emits approximately 93 kg CO₂ per MMBtu; lignite emits more.
- In power generation, the gap widens because modern combined-cycle gas turbines (CCGT) operate at higher thermal efficiency (55–63%) than most coal plants (typically 33–42%).
Net of efficiency, a modern CCGT typically emits around 40–50% less CO₂ per kilowatt-hour generated than an average coal plant, with the exact figure depending on plant vintage and operating mode. This is the figure often cited to justify replacing coal with gas for power generation.
Lifecycle, not just combustion
Combustion is only part of the story. A full lifecycle comparison includes:
For LNG
- Upstream production, including methane leakage from wells, pads, and gathering systems.
- Pipeline transport to the liquefaction plant.
- Liquefaction energy and combustion CO₂ at the export plant (roughly 8–10% of feed gas energy).
- Shipping, with fuel combustion and methane slip.
- Regasification at the import terminal.
- End-use combustion in the power plant or industrial user.
For coal
- Mining emissions, including methane released from coal seams (sometimes significant for deep underground mines).
- Bulk transport by rail, truck, barge, or ship (coal is energy-dense enough that long-distance shipping is tractable).
- End-use combustion, producing CO₂ plus larger quantities of local air pollutants.
- Ash handling and disposal, with associated land-use and water-quality implications.
For LNG, the critical lifecycle variable is upstream methane leakage. Below roughly 2–3% leakage (depending on assumptions about warming potential and efficiency), LNG retains a meaningful climate advantage over coal on both 20-year and 100-year timescales. As leakage rises toward and above that range, the 20-year climate advantage erodes and in some studies can disappear. See Methane emissions for how leakage is measured and reduced.
Local air quality
On local air pollutants, the gap between gas and coal is typically larger than on CO₂ alone:
- Sulphur dioxide (SO₂). Natural gas contains very little sulphur after pre-treatment. Modern coal plants use flue-gas desulphurisation ("scrubbers"), but even scrubbed coal emits more SO₂ per kWh than gas.
- Nitrogen oxides (NOx). Both fuels produce NOx, but modern gas turbines with dry low-NOx burners and SCR systems operate at lower NOx per kWh than typical coal fleets.
- Particulate matter (PM2.5 and PM10). Coal combustion produces substantially more primary and secondary particulates than gas combustion, even with electrostatic precipitators and fabric filters.
- Mercury and heavy metals. Coal contains trace mercury and other metals that are released on combustion; gas does not.
For people living near power plants, the health differences — reduced PM2.5 exposure and fewer SO₂-related acid aerosols — are often the most directly tangible benefit of a gas-for-coal switch.
Water
Water-use patterns differ in both directions:
- Coal plants typically have large cooling-water demands (once-through or closed-cycle) and also require water for ash handling and flue-gas desulphurisation. Once-through cooling can have significant thermal and biological impacts on source water bodies.
- CCGTs have lower absolute water needs per kWh than coal plants, and some modern designs use air cooling that eliminates most water withdrawal — at a thermodynamic penalty.
- LNG-specific water effects arise at regasification terminals using open-loop seawater vapourisation, which warms and returns large volumes of seawater; and at upstream gas production, particularly unconventional operations, which can be water-intensive through hydraulic fracturing.
Economics
Head-to-head economics depend on fuel prices, which vary by region and over time. Structural differences are more durable:
- Capital cost. CCGTs typically have lower overnight capital cost per kilowatt than new coal plants.
- Build times. CCGTs are faster to build than new pulverised-coal plants, meaning gas can ramp faster into a market where demand grows quickly.
- Fuel cost sensitivity. Gas plants have higher fuel cost as a share of total generating cost than coal plants, so they are more exposed to gas-price volatility. Long-term LNG contracts partially mitigate this for countries that rely on imports.
- Flexibility. CCGTs and simple-cycle gas turbines are more flexible than most coal plants — faster to ramp and better suited to balancing variable renewables.
Context: neither fuel is zero-carbon
A final framing point matters. Comparing LNG with coal is useful but narrow. Both fuels are fossil, and any durable path to large reductions in power-sector emissions must eventually lead away from both toward renewables (wind, solar, hydro), nuclear, and potentially hydrogen-based or geothermal generation — paired with the storage and transmission needed to make them reliable. LNG's climate case is frequently framed as a "bridge" while that transition is built. Whether that framing is borne out in a specific country depends on the pace of electrification, the credibility of methane-reduction programmes, and the speed at which zero-carbon alternatives become available at scale.