Which type of fuel is most polluting?

Coal—especially lignite (brown coal)—is the most polluting fuel overall, producing the highest greenhouse-gas emissions per unit of energy and the greatest loads of harmful air pollutants like sulfur dioxide, particulate matter, and mercury; oil is next, while natural gas is lower but can be climate-worse than coal if methane leakage is high. This assessment reflects both direct combustion and full life-cycle impacts and remains consistent with current findings from the IPCC, IEA, and environmental agencies.

How to define “most polluting”

“Most polluting” depends on what harms you measure. Policymakers and scientists usually look at climate and air-quality impacts across a fuel’s life cycle—from extraction and processing to combustion and waste.

• Greenhouse-gas intensity: total CO2-equivalent emissions per unit of energy or electricity (e.g., gCO2e/kWh).
• Air pollutants that harm health: sulfur dioxide (SO2), nitrogen oxides (NOx), fine particles (PM2.5), volatile organics, and toxic metals like mercury and arsenic.
• Life-cycle and upstream impacts: methane leakage, land disturbance, water use/contamination, and waste (e.g., coal ash).
• Temporal effects: short-term warming (e.g., methane, black carbon) versus long-term CO2 accumulation.

Taken together, these dimensions consistently place coal at the top of the pollution scale, with lignite being the worst variant due to its low energy density and high moisture content.

The ranking at a glance

Across the main metrics, coal is the dirtiest fuel used at scale. Oil follows, and natural gas is generally less polluting but not “clean”—particularly if methane leaks are poorly controlled. A few niche fuels can be even worse than coal in specific ways, but they are used far less globally.

• By life-cycle climate impact (electricity): lignite/hard coal are highest (about 820–1,100+ gCO2e/kWh); oil-fired power is lower than coal but high (roughly 650–780 gCO2e/kWh); modern combined-cycle gas is lower still (about 450–520 gCO2e/kWh), but high methane leakage can erase this advantage on a 20-year climate horizon.
• By direct CO2 per unit energy: coal emits the most (≈95 kg CO2 per GJ, depending on grade), oil is mid-range (≈73 kg/GJ), and natural gas is lowest among fossil fuels (≈56 kg/GJ), based on IPCC default factors.
• By air pollutants/toxins: coal combustion leads in SO2, PM2.5, and mercury emissions. Heavy fuel oil used in shipping is also extremely high in SOx unless low-sulfur fuel or scrubbers are used (stricter limits have applied globally since 2020).
• Special cases: peat and oil shale can be even more CO2-intensive than coal, but their global use is limited; they do not change the overall conclusion for fuels used at scale.

This ranking reflects both the intensity of emissions and the breadth of harms. Coal dominates on multiple fronts, making it the most polluting mainstream fuel.

Greenhouse-gas emissions per unit of electricity

For climate impact, life-cycle assessments (mining, processing, transport, combustion, and upstream leaks) show coal at the top. Lignite typically performs worse than hard coal because it contains more moisture and yields less energy per ton, raising CO2 per kWh generated.

• Coal (all types): median ≈820 gCO2e/kWh; lignite plants often exceed 1,000 gCO2e/kWh depending on technology and controls (IPCC and IEA assessments).
• Oil-fired power: ≈650–780 gCO2e/kWh; used less in power generation today but still prevalent in some regions and backup applications.
• Natural gas (combined-cycle): ≈450–520 gCO2e/kWh with typical upstream leakage; if methane leakage rises to roughly 3% or more by volume, gas can rival or exceed coal on 20-year warming potential.

While carbon capture and storage (CCS) can reduce stack emissions from coal and gas, real-world projects remain limited, costly, and do not address all upstream or non-CO2 pollutants, so the baseline ranking remains unchanged today.

Air pollutants and toxins

For air quality and health, coal performs worst because it emits high levels of sulfur and particulate matter and releases toxic metals. Controls (scrubbers, filters, low-sulfur fuels) can cut pollutants, but many plants—especially older ones—lack best-available technologies, and mining/ash disposal create additional risks.

• Sulfur dioxide (SO2): Coal is the largest source among common fuels; SO2 contributes to acid rain and secondary fine particles. Heavy fuel oil also has high sulfur unless regulated.
• Nitrogen oxides (NOx): All combustion sources produce NOx, but coal plants are major contributors without advanced controls; NOx forms smog and secondary PM2.5.
• Particulate matter (PM2.5/PM10): Coal emits high primary particulates; gas combustion emits far less PM at the point of use.
• Toxic metals and organics: Coal releases mercury, arsenic, lead, and polycyclic aromatic hydrocarbons; coal ash can contaminate water if mismanaged.
• Natural gas: Very low SO2 and PM at combustion, but upstream operations can emit methane and volatile organics that affect ozone and health.

These pollutants drive respiratory and cardiovascular disease burdens, with coal-heavy regions experiencing the highest health costs from energy use.

Notable exceptions and edge cases

Some fuels or situations can rival or exceed coal on particular metrics, but they do not overturn the general conclusion for mainstream energy use.

• Peat and oil shale: Often higher CO2 per unit energy than coal and destructive to landscapes; global use is comparatively small.
• Heavy fuel oil in shipping: Extremely high sulfur historically; since 2020, the IMO sulfur cap (0.5% globally, 0.1% in emission control areas) has cut SOx unless ships use scrubbers and continue burning high-sulfur fuel.
• Methane leakage from gas: High leakage—especially over short timeframes—can make gas’s near-term climate impact comparable to or worse than coal; rigorous leak detection and repair are critical.
• Household biomass and coal: In homes without clean stoves, both can cause severe indoor and local air pollution; modern district-scale biomass with controls is far cleaner than traditional stoves.
• Uncontrolled diesel and flaring: Produce significant black carbon and local pollutants, with large short-term climate and health impacts.

These cases illustrate that context matters, but they reinforce—not weaken—the overall case against coal for both climate and health.

Implications for policy and choices

Because coal is the most polluting fuel, the biggest immediate gains come from cutting coal use and tightening pollution controls, while also addressing methane from the gas supply chain.

• Accelerate coal retirements and halt new unabated coal plants; prioritize replacing coal with renewables, storage, demand response, and efficient electrification.
• Deploy best-available controls (scrubbers, fabric filters, low-NOx burners) where coal persists temporarily; manage coal ash safely.
• Cut methane leaks in oil and gas with detection, repair, and equipment upgrades; this is one of the fastest ways to slow near-term warming.
• Continue sulfur limits in shipping and shift to cleaner marine fuels or electrification where feasible.
• Support just transitions for workers and communities dependent on coal, and invest in clean energy infrastructure.

These steps deliver outsized climate, health, and economic benefits compared with almost any other fuel-focused actions.

Summary

Among widely used fuels, coal—especially lignite—is the most polluting by both climate and air-quality measures; oil follows, and natural gas is lower but still significant, with methane leakage a crucial variable. A few niche fuels (peat, oil shale) can be even worse on specific metrics, and heavy fuel oil is highly polluting without sulfur controls. Cutting coal use, controlling methane, and scaling clean energy are the most effective ways to reduce fuel-related pollution quickly.

What is the dirtiest fuel source?

coal
Again, coal is the dirtiest fuel. It emits much more greenhouse gases than other sources — more than a hundred times more than nuclear. Oil and gas are also much worse than nuclear and renewables but to a lesser extent than coal.

What are the top 3 contributors to CO2 emissions?

The majority of this increase has resulted from increased fossil fuel consumption and industrial emissions. Agriculture, deforestation, and other land-use changes have been the second-largest contributors. Emissions of non-CO2 greenhouse gases (CH4, N2O, and F-gases) have also increased significantly since 1850.

Which fuel is the most polluting?

Coal
Coal is a fossil fuel, and is the dirtiest of them all, responsible for over 0.3C of the 1C increase in global average temperatures. This makes it the single largest source of global temperature rise. Oil releases a huge amount of carbon when burned – approximately a third of the world’s total carbon emissions.

What is the #1 polluter on planet Earth?

China is the world’s biggest annual greenhouse gas polluter, responsible for nearly a third of global emissions, followed by the United States and India. While China leads in absolute annual emissions, the per capita emissions ranking changes, with countries like Qatar and the United States having higher per person pollution levels due to large individual energy consumption.
 
Absolute vs. Per Capita Emissions

• Absolute Emissions: Opens in new tabThis measures the total amount of pollution from a country. China emits the most carbon dioxide (CO2) annually. 
• Per Capita Emissions: Opens in new tabThis measures the pollution per person in a country. When looking at this metric, countries like the United States, Qatar, and Montenegro have higher emissions per person than China, which has a large population. 

Top Polluters by Annual Emissions

1. China: The largest annual emitter of greenhouse gases, accounting for roughly one-third of the world’s total. 
2. United States: The second-largest annual polluter. 
3. India: The third-largest annual polluter. 

Other Factors

• Historic vs. Current Emissions: Opens in new tabThe total historical contribution to climate change is another important factor to consider. 
• Efforts to Reduce Emissions: Opens in new tabDespite being the top polluter, China is making significant efforts to reduce its emissions by rapidly expanding renewable energy sources like wind and solar.