The United States and much of the world was built on coal. From early steamboats to today’s massive power plants, coal has provided a cheap and widely available source of energy for more than a century.
But like the person who keeps throwing trash in their backyard until the smell becomes unbearable, the real impact of coal is finally becoming impossible to ignore. So, just how bad is it?
Since it’s hard to visualize millions of tons of anything, let’s put the question to more personal terms: What is coal’s environmental impact from powering your home for a month? The average US home uses 914 kilowatt hours (kWh) per month so we will round this up to 1,000 kWh to keep things simple (1,000 kWh is the same as 1 megawatt hour).
How much coal is burned to generate 1 MWh of electricity?
It takes 1,100 pounds of coal to generate 1 MWh of electricity, enough coal to fill a hot tub.
Let’s look at the environmental impact of this coal in terms of carbon dioxide, pollution, greenhouse gas emissions, and physical wastes, as well as the land used in mining and water used to cool power plants.
Here’s a quick synopsis of the pollution and greenhouse gases from that megawatt hour of electricity that lights and cools your house for a month:
- 2,100 pounds of carbon dioxide
- 346 pounds of methane
- 185 pounds of coal ash
- 3.9 pounds of sulfur dioxide
- 1.6 pounds of nitrogen oxides
- 1.7 ounces of radioactive uranium and thorium
- 13 mg of mercury (nasty stuff)
- 16,000 gallons of fresh water
- 3.75 square feet of strip mining
One MWh of coal power creates 2,100 pounds of CO2 emissions
Coal’s most notorious byproduct is carbon dioxide (CO2). Each megawatt hour of electricity from coal power plants emits 2,100 pounds of CO2 (960 kg), more than a ton!
But wait, how can 1,100 pounds of coal produce twice its weight in CO2? An article from the US Energy Information Adminstration explains this in detail but, in short, it’s because the carbon atoms in coal are each combined with two atoms of oxygen from the air to form the CO2. In other words, the CO2 from burning coal gets most of its weight from the air.
The 2,100 pounds of CO2 would fill five 18-wheeler trucks.
Mining a MWh worth of coal releases 346 pounds of methane (CH4)
Methane (CH4) is usually associated with natural gas. Indeed, most unwanted methane leaks come from gas wells and pipelines. But many people are surprised to learn that coal mining is also a very large source of this greenhouse gas. Since methane is far more environmentally damaging than CO2, atmospheric methane is usually expressed as a CO2 equivalent, or CO2e. Using this approach, coal mining releases 346 pounds (CO2e) of methane per 2,100 pounds of coal, enough to generate a MWh of electricity. The EPA says:
By 2020, global methane emissions from coal mines are estimated to reach nearly 800 MMTCO2E, accounting for 9 percent of total global methane emissions.
Generating 1 MWh with coal leaves behind 185 pounds of coal ash
Coal ash is the solid byproduct left over after coal is burned. Every megawatt hour generated in a coal plant leaves behind 185 pounds of ash.
According to the American Coal Ash Association, coal power plants created 102 million tons of ash in 2018, making it the second-largest source of waste in the US after trash. While 58% was recycled into things like cement and wallboard, the remaining ash was mixed with water and dumped into ponds. The EPA reports there are more than 1,000 coal ash ponds scattered across the country, covering almost 75,000 acres. Together, they store more than 2 billion tons of ash, enough to cover the entire state of Rhode Island waist-high (ACA).
Burning 1 MWh of coal emits 3.9 pounds of sulfur dioxide
Sulfur dioxide (SO2) is one of the main causes of acid rain (EPA). Coal plants are the largest source of SO2, creating 64% of all human-emitted SO2 in 2014 (DOE). Thanks to increased regulations and power plant upgrades, as well as the rapid shift to natural gas, SO2 emissions have been declining sharply over the last two decades, releasing only 2.2 million tons in 2018.
Coal plants emit 1.6 pounds of nitrogen oxides for every MWh
What about nitrogen oxides (NOx and NO2)? These pollutants lead to acid rain, aggravate respiratory diseases, and create the smog we see hanging over cities (EPA). In 2018, coal plants created 931 thousand tons of NOx.
1.7 ounces of radioactive uranium and thorium is leftover from a MWh of coal power
The geologic processes that create coal also concentrate a range of trace materials into these black rocks. A study by the US Geologic Survey of 2,300 coal sites found the majority had concentrations of uranium between 1 and 4 parts per million. Similar results were found for thorium. Averaging this to 2.5 ppm for both elements leaves us with 5 ppm of radioactive materials per ton of coal. Even small numbers of these heavy atoms leave behind a measurable level of radioactive material.
While the concentration of these heavy elements varies tremendously across the world, it’s useful to look at overall averages. It turns out that electrifying your house leaves behind about 1.7 ounces of thorium and uranium each month, about the same weight as 8 US quarters (Freeing Energy). In some places, the concentrations can be 6-7 times higher – so high that at least one mining company is finding it cheaper to extract uranium from coal ash than uranium mines.
Just how dangerous is this radiation? Most research says not much at all. Remember, there is already a lot of natural background radiation and all the material from coal ash is caught and stored within the plant (at least in the US). So, even if you live within a mile of a coal plant, you will only increase your exposure to radiation about 5% a year, less than an x-ray.
More interesting is that nuclear plants have far less radiation. A widely cited paper by Alex Gabbard, of Oakridge National Laboratory, found that the radioactivity outside a coal plant is up to 100-times higher than a nuclear plant. This is largely due to the safety regulations governing the nuclear industry (see: What are the risks of radiation from nuclear power plants?)
Coal plants leave behind 13 milligrams of mercury per MWh
Coal plants released 22 tons of mercury in 2014 – the last year any data was released (EPA). This is half of all human-released mercury (EPA). Many people have had the mercury in broken thermometer touch their skin without incident – so what’s the problem? When mercury (Hg) gets into the environment, which happens all too often from coal plants, it can readily combine with other elements becoming one of the most toxic substances on earth.
Mercury has a mean lethal dose (LD50) of 1 mg/kg. This means 62 mg of mercury can be lethal to 50% of people, assuming the average weight of a person is 62 kg. In terms of your monthly electricity consumption, five months of powering your house leaves behind 65 mg of mercury, enough to kill an average-sized human being. Yikes. Of course, this is just illustrative. You’d have to eat almost 1,000 pounds of coal ash to get this much mercury and, if you did, mercury would be the least of your issues.
But the story of researcher Karen Wetterhahn is a cautionary tale. She tragically died after only a drop or two of a particularly lethal compound of mercury fell on her hand. Despite wearing latex gloves, the mercury seeped through to her skin in a matter of seconds and she later died.
Mining coal and cooling plants uses 16,300 gallons per MWh
If your home were powered entirely by coal plants, it would take 150 gallons of water per month to mine the 1,100 pounds of raw coal. Cooling the power plant uses a far larger amount of water: 16,150 gallons per MWh, enough to fill an average size swimming pool. For many coal plants, this volume is “pass through”, meaning the water is extracted from a river or lake, used to cool the power plant, and then returned into th environment. But, some plants actually “consume” the water, meaning it is evaporated and lost to the ecosystem. On average, about 300 gallons of water are “consumed” for coal plants per MWh of electricity generated/
To see how water consumption compares across every kind of power plant, check out: Energy Fact; Solar and wind use 250-times less water than coal and nuclear plants.
Strip mining the coal for 1 MWh requires 3.75 square feet of land
The most visible impact of coal power is the land used for strip mining. While 3.75 square feet per MWh may seem tiny, a century of mining and billions of MWh’s has accumulated into 8.3 million acres of impacted land (the government does not track strip mining land so this is based on research from environmental organizations).
Our civilization … is founded on coal, more completely
than one realizes until one stops to think about it. The machines that
keep us alive, and the machines that make machines, are all directly or
indirectly dependent upon coal. In the metabolism of the Western world
the coal-miner is second in importance only to the man who ploughs the
From the 1937 book, The Road to Wigan Pier, by George Orwell, as referenced in Vaclav Smil’s book, Energy and Civilization.
- EIA: Annual coal report
- Freeing Energy: Ever wonder why we use so much coal? America was built on it.
- Freeing Energy: How is coal formed?
- Freeing Energy: Five trends that will lead to the end of fossil fuels
Note: There are numerous sources of information on the topic of coal byproducts. The math is shown here to help explain how our numbers were derived but it is inevitable that other approaches will yield different results. If you find a glaring mistake, please let us know in the comments below.
Also note: we use the US government data wherever possible. Many environmental groups do their own studies and find pollution is often worse than reported by the government. Our goal here is to bring as many people as possible into these conversations so we avoid using data that could be perceived as biased.