Coal is the single most carbon-intensive way to generate electricity, producing roughly 2.6 times more CO2 per kilowatt-hour than natural gas and infinitely more than wind or solar during operation. Its damage extends well beyond climate change: coal pollutes air and water, poisons ecosystems with heavy metals, and has killed hundreds of thousands of people through particulate emissions alone. Here’s a closer look at the specific ways coal causes harm.
Coal Is the Biggest Driver of Energy-Related CO2
Burning coal to produce one kilowatt-hour of electricity releases about 2.25 pounds of CO2, compared to 0.86 pounds for natural gas. Wind, solar, hydro, and nuclear produce no CO2 at the point of generation, with only minor upstream emissions from manufacturing equipment and fuel processing. That makes coal roughly two and a half times dirtier than the next most common fossil fuel and orders of magnitude worse than renewables.
The climate damage doesn’t stop at CO2. Coal mining itself is responsible for over 10% of all human-caused methane emissions worldwide, releasing an estimated 33 to 41 million metric tons of methane per year. Methane has a much shorter lifespan in the atmosphere than CO2, lasting about a decade rather than centuries, but it traps far more heat per molecule during that time. Cutting methane from coal mines is one of the fastest ways to slow the rate of warming, which is why it gets attention from climate scientists separate from CO2 reduction.
Coal Pollution Kills Tens of Thousands of People
Coal-fired power plants emit fine particulate matter known as PM2.5, tiny particles small enough to pass through your lungs and into your bloodstream. A major study examining U.S. Medicare data from 1999 to 2020 found that 460,000 deaths were attributable to coal-generated PM2.5 during that period. The vast majority of those deaths, about 390,000, occurred between 1999 and 2007, when coal burning was at its peak and regulations were weaker. During those years, coal particulates killed an average of more than 43,000 Americans annually.
What makes coal pollution especially dangerous is its potency relative to other sources of fine particulate matter. Harvard researchers calculated that a small increase in coal-sourced PM2.5 was associated with a 1.12% rise in all-cause mortality, a risk 2.1 times greater than the same amount of PM2.5 from any other source. In other words, particles from coal smoke are roughly twice as deadly as equivalent particles from vehicle exhaust or industrial sources. Stricter emissions regulations and coal plant closures brought the annual death toll down dramatically, to about 1,600 by 2020, but coal remains a significant source of air pollution globally.
Acid Rain, Smog, and Mercury
When coal burns, it releases sulfur dioxide and nitrogen oxides into the atmosphere. These gases react with water vapor to form sulfuric and nitric acid, which fall back to earth as acid rain. Acid rain damages forests, acidifies lakes and streams, corrodes buildings, and degrades soil quality. Nitrogen oxides also combine with volatile organic compounds in sunlight to create ground-level ozone, the main ingredient in smog, which triggers asthma attacks and reduces lung function.
Coal is also a major source of mercury pollution. Stationary coal combustion accounts for 21% of all human-caused mercury emissions worldwide, making it the second-largest source after small-scale gold mining. Mercury released into the air eventually settles into waterways, where bacteria convert it into methylmercury. This accumulates in fish and moves up the food chain. For people who eat contaminated fish regularly, methylmercury exposure can cause neurological damage, and it’s particularly harmful to developing fetuses and young children.
Coal Ash Contains Heavy Metals
After coal is burned, the leftover material is coal ash, a mix of powdery fly ash and heavier bottom ash. Coal ash contains a cocktail of heavy metals including cadmium, chromium, copper, lead, nickel, zinc, and manganese. The finest particles, those smaller than about 54 micrometers, tend to concentrate the highest levels of these metals, and cadmium poses the greatest ecological risk despite being present in lower concentrations than the others.
Coal ash is typically stored in massive surface ponds or landfills, and these storage sites can leak. When heavy metals seep into groundwater or spill into rivers, they contaminate drinking water supplies and aquatic ecosystems. The U.S. has seen several catastrophic coal ash spills, and even routine seepage from unlined storage ponds has been linked to elevated levels of arsenic, selenium, and other toxins in nearby wells.
Mining Destroys Landscapes and Waterways
The environmental damage from coal starts long before it reaches a power plant. Mountaintop removal mining, the dominant form of surface mining in Appalachia, involves stripping away forest cover, blasting through rock layers to reach coal seams, and dumping the excess rock into adjacent valleys. Between 1976 and 2015, surface coal mining transformed an estimated 5,900 square kilometers of Central Appalachia, roughly 7.1% of the entire region. Watersheds affected by mountaintop removal have lost most of their forest cover. Some impacted areas retain as little as 8% forest, with the rest converted to barren land.
The valley fills created by dumped rock and soil bury stream channels entirely, eliminating aquatic habitat and altering water chemistry for miles downstream. Streams below mining sites carry elevated levels of sulfates, selenium, and other dissolved minerals that are toxic to aquatic life. This isn’t temporary disruption. Even after “reclamation,” the landscape rarely returns to anything resembling its original ecosystem within a human lifetime.
Coal Uses Enormous Amounts of Water
Coal-fired power plants require vast quantities of water for cooling. In the U.S., coal plants withdraw an average of 19,185 gallons of water per megawatt-hour of electricity produced. Natural gas combined-cycle plants, by comparison, use about 2,803 gallons per megawatt-hour. That means coal consumes nearly seven times more water than gas for the same amount of electricity. In regions already facing water scarcity, this level of consumption puts additional stress on rivers, lakes, and aquifers that communities and agriculture also depend on.
Coal Is No Longer Economically Competitive
Beyond its environmental and health costs, coal has simply become more expensive than the alternatives. The U.S. Energy Information Administration’s 2025 outlook doesn’t even include new coal plants in its cost comparisons anymore, replacing them with natural gas options instead. For new power plants entering service in 2030, onshore wind is projected to cost about $26 per megawatt-hour, solar about $38, and natural gas combined-cycle about $46. New coal generation can’t compete with any of these.
This economic reality is reshaping global energy markets. The International Energy Agency forecasts that global coal demand has plateaued and will edge downward through 2030, returning to 2023 levels. Coal-fired power generation is expected to decline starting in 2026 as renewable capacity surges, nuclear power expands, and a wave of new liquefied natural gas enters the market. The shift isn’t driven purely by policy. It’s driven by the fact that building new wind and solar is now cheaper than running existing coal plants in many regions.