By Karin Kirk for Yale Climate Connection.
Broadcast version by Laura Hatch for Big Sky Connection reporting for the Yale Climate Connection-Public News Service Collaboration
On September 2, 2023, a specially equipped aircraft flew to Colstrip, Montana. On this fine late summer morning, the plane flew over the Colstrip coal-fired power plant, one of the largest and dirtiest in the U.S. The plant was generating about 1,500 megawatts of electricity that day.* The airplane flew back and forth in tidy parallel paths, making 12 passes over the power plant and its surroundings.
The airplane is called the Global Airborne Observatory, and it measures climate-warming pollution in pinpoint detail. Data from the flyover revealed a billowing plume of carbon dioxide coming from Colstrip’s twin smokestacks, with concentrations reaching beyond 100,000 parts per million. These measurements showed the power plant was emitting about 1.7 million pounds of CO2 an hour, which is what you’d get from burning 4.4 railcars full of coal.
The result of the flyover is a visual representation of climate-warming pollution that conveys something that numbers cannot. Most readers already know that a coal-burning power plant is a major source of CO2 emissions. But it strikes a different chord to see a plume of pollution emerging from a power plant and spreading silently over the landscape.
As the Trump administration moves to cancel greenhouse gas reporting by major polluters, a constellation of satellites and aircraft is already taking up the slack. Scores of instruments are peering down through Earth’s atmosphere, finding pollution all across the globe, every day. These programs are run by private companies, nonprofits, and governments, and most of them display their data for free so anyone can see it.
Carbon Mapper shines a light on CO2 and methane
Carbon Mapper is one of the easiest-to-use tools for observing greenhouse gas pollution. One of the strengths of Carbon Mapper is that it combines data from multiple sources, both government and privately operated missions. Carbon Mapper uses data from three aircraft, NASA’s EMIT instrument on the International Space Station, and a satellite called Tanager-1.* The Tanager satellite is owned and operated by Planet Labs, PBC, which partnered with Carbon Mapper to develop the satellite. The findings are displayed in a free mapping tool.
Snapshots from above capture a different view than EPA reporting
EPA reporting can be based on direct measurements at some facilities, or a calculation called an “inventory.” An inventory is simply the sum of the amount of fossil fuel burned, multiplied by an average emissions factor for the type of fuel, such as coal, gas, or oil.
Riley Duren, CEO of Carbon Mapper, said that inventory-style measurements don’t capture the full picture.* For example, if a power plant generates the same amount of power on two different days, one might reasonably calculate the same rate of emissions. But that’s not necessarily true, said Riley. For every megawatt of power generated, the emissions can vary due to the efficiency of the power plant’s combustion. Riley said that a standardized emissions calculation doesn’t capture these variations, and “outliers can dramatically change the emission rate.”
Riley expects satellite monitoring will generate more accurate measurements of CO2 and methane pollution than inventory calculations, and satellites can fill in gaps in countries with no emissions reporting. This data will become more robust as more satellites are added to the fleet. Carbon Mapper plans to launch three new satellites, and Carbon Mapper is just one of several programs that are finding and mapping climate-warming pollution.
Coal plants are the largest CO2 super-emitters in the U.S.
In the U.S., the largest plumes of CO2 pollution are all coming from coal-burning power plants. In fact, the map of the country’s worst emitters looks exactly like a map of the places that still rely on coal to generate electricity.
The list below shows the largest CO2 polluters in the U.S. in the Carbon Mapper database, as of August 2025. More details about these super-emitters are listed in the table at the bottom of this article, and the links for each power plant take you directly to that facility in Carbon Mapper’s data portal.
1. Labadie Energy Center-Labadie, Missouri, emits 2,646,000 pounds of CO2 per hour, the equivalent of burning 6.7 railcars of coal per hour
2. Coal Creek Power Station-Underwood, North Dakota, emits 2,425,500 pounds of CO2 per hour, the equivalent of burning 6.1 railcars of coal per hour
3. Oak Grove Steam Electric Station-Franklin, Texas, emits 1,905,800 pounds of CO2 per hour, the equivalent of burning 4.8 railcars of coal per hour
4. Jim Bridger Power Plant-Rock Springs, Wyoming, emits 1,847,300 pounds of CO2 per hour, the equivalent of burning 4.6 railcars of coal per hour
5. Colstrip Generating Plant-Colstrip, Montana, emits 1,663,700 pounds of CO2 per hour, the equivalent of burning 4.2 railcars of coal per hour
6. Iatan Generating Station-Weston, Missouri, emits 1,502,700 pounds of CO2 per hour, the equivalent of burning 3.8 railcars of coal per hour
7. Robert W. Scherer Power Plant-Juliette, Georgia, emits 1,498,100 pounds of CO2 per hour, the equivalent of burning 3.8 railcars of coal per hour
8. James H. Miller Electric Generating Plant-Adamsville, Alabama, emits 1,255,500 pounds of CO2 per hour, the equivalent of burning 3.2 railcars of coal per hour
9. Fayette Power Project, aka Sam Seymour Power Plant-La Grange, Texas, emits 1,222,000 pounds of CO2 per hour, the equivalent of burning 3.1 railcars of coal per hour
10. Four Corners Steam Electric Station-Waterflow, New Mexico, emits 1,207,900 pounds of CO2 per hour, the equivalent of burning 3 rail cars of coal per hour
Karin Kirk wrote this story for Yale Climate Connection.
