What is the Environmental Impact of Geothermal Energy?
Geothermal energy has one of the smallest environmental footprints of any electricity source, but it is not impact-free. A geothermal power plant emits roughly 38 to 76 grams of CO2 equivalent per kilowatt-hour across its life cycle, against about 450 grams for natural gas and close to 1,000 grams for coal. It uses less land per unit of electricity than solar or wind, and an air-cooled plant consumes less water than a coal or nuclear station. The real trade-offs sit elsewhere: hydrogen sulfide in the steam, land subsidence at older fields, and earthquakes triggered by injecting water underground.
This guide gives the measured numbers for each of those effects, names the projects where they went wrong, and explains what enhanced geothermal changes in 2026.
Does geothermal energy cause pollution?
Yes, but far less than any fossil fuel. Geothermal power produces air emissions because the geothermal fluid pulled from underground carries dissolved gases with it. The main ones are carbon dioxide, hydrogen sulfide, methane, ammonia, and boron. What reaches the atmosphere depends almost entirely on the plant design.
Open-loop flash and dry-steam plants vent some of those gases. Binary and closed-loop systems keep the geothermal water in a sealed circuit, transfer its heat to a second working fluid, and reinject everything, so their air emissions are close to zero. Hydrogen sulfide is the pollutant of greatest concern: dry-steam plants release roughly 0.0002 pounds per megawatt-hour, while flash plants release about 0.35 pounds per megawatt-hour. Both figures are a fraction of what a coal plant emits in sulfur dioxide.
Some operators go further and put the gases back underground. The CarbFix project at Iceland’s Hellisheidi plant dissolves the plant’s own exhaust in water and injects it into basalt, where it mineralizes. It captures roughly 34% of the plant’s CO2 and about 60% of its hydrogen sulfide.
How much carbon dioxide does geothermal energy produce?
Life-cycle emissions for geothermal electricity cluster around 38 to 45 grams of CO2 equivalent per kilowatt-hour in NREL’s assessments, which puts it in the same band as wind and below solar photovoltaics. The spread across real fields is wide, because it depends on how much gas is dissolved in the reservoir. The New Zealand Geothermal Association reports a range of 21 to 341 grams per kilowatt-hour with an average of 76.
| Electricity source | Life-cycle CO2e (g/kWh) | Notes |
|---|---|---|
| Geothermal (binary, closed-loop) | Near zero at the plant | Gases reinjected, not vented |
| Geothermal (typical, all types) | 38 to 76 | NREL central estimates; field range 21 to 341 |
| Wind | ~11 to 12 | Mostly manufacturing and construction |
| Solar photovoltaic | ~40 to 50 | Mostly panel manufacturing |
| Natural gas | ~450 | Combustion dominates |
| Coal | ~1,000 | Roughly 13 to 26 times geothermal |
One caveat worth keeping: a handful of high-gas reservoirs in Turkey and Italy sit at the top of that 341-gram range, which is closer to a gas plant than to wind. Geothermal is low-carbon as a category, not automatically low-carbon at every site.
How much land does a geothermal plant use?
Less than any other renewable. This is the reverse of a claim that circulates widely, including in an earlier version of this page: that geothermal occupies more ground than other generation. The measured data says otherwise. A geothermal facility occupies roughly 7.5 square kilometers per terawatt-hour generated. Solar thermal needs about double that, solar photovoltaic close to five times, and wind close to ten times. Measured per megawatt of capacity, a geothermal plant typically needs 1 to 8 acres including wells, pipelines, and the powerhouse.
| Source | Approximate land use per TWh | Relative to geothermal |
|---|---|---|
| Geothermal | ~7.5 km2 | Baseline |
| Solar thermal | ~15 km2 | About 2x |
| Solar photovoltaic | ~37 km2 | About 5x |
| Wind (total project area) | ~75 km2 | About 10x |
The amount of land required is small, but where that land sits matters. Productive geothermal resources cluster in volcanic and tectonically active terrain, and those places are often protected. Yellowstone’s geysers and fumaroles have statutory protection precisely because drilling nearby can drain the plumbing that feeds them. In the United States, a federal geothermal project triggers review under the National Environmental Policy Act before it is permitted.
How much water does geothermal energy use?
It depends on the cooling system, and the range is enormous. Air-cooled geothermal plants consume under 200 gallons per megawatt-hour. Water-cooled plants consume anywhere from 500 to 5,000 gallons per megawatt-hour, which is why a single “geothermal uses X gallons” figure is misleading. For comparison, a closed-loop coal plant consumes roughly 500 to 600 gallons per megawatt-hour and a closed-loop nuclear plant 700 to 1,100.
The more important distinction is what kind of water. Geothermal fluid is typically brackish, high in salt and sulfur, and not drinkable, so a plant running on its own reinjected geothermal water is not competing with drinking supplies. Enhanced geothermal systems are stingier still, with long-term consumption of roughly 14 gallons of degraded water per megawatt-hour over a 30-year well life. The Geysers field in California goes one better and injects treated municipal wastewater from nearby Santa Rosa and Lake County into the reservoir, turning a disposal problem into reservoir pressure support.
Can geothermal energy cause earthquakes?
Yes. Injecting water into hot rock changes pore pressure along existing faults, and that can trigger seismic events. Induced seismicity is the most serious environmental objection to geothermal development, and it is the reason two flagship projects were shut down.
Two projects define the risk. The Basel Deep Heat Mining project in Switzerland triggered more than 10,000 events during stimulation in December 2006, the largest reaching magnitude 3.4, felt across the city; the project was cancelled outright in December 2009. In November 2017 a magnitude 5.5 earthquake struck Pohang, South Korea, injuring dozens and damaging buildings, and a government investigation panel concluded it was triggered by the nearby enhanced geothermal project. It remains the largest earthquake attributed to geothermal operations anywhere.
Routine operation looks different from stimulation. The Geysers geothermal field in California generates tens of thousands of microseismic events per year, but they cluster between magnitude 0.5 and 3.0, and machine-learning catalogs that detect roughly 60,000 events annually find the great majority are too small to feel. The industry response is traffic-light protocols: continuous seismic monitoring with pre-agreed injection cutbacks and shutdowns as magnitudes climb. Fervo Energy and other next-generation developers now design around them from the start.
Does geothermal drilling cause land subsidence?
It can, when fluid is withdrawn faster than it is replaced. The reference case is Wairakei in New Zealand, which began producing in 1958 without reinjection. The center of its subsidence bowl has dropped roughly 14 meters over about 50 years, damaging pipelines, drains, roads, power lines, and a local hotel. Subsidence rates there fell from over 450 millimeters per year in the 1970s to 80 to 90 millimeters per year by the 2000s once management changed.
Reinjection is the fix, and it is now standard. Fields designed with reinjection from day one, such as Ngawha in New Zealand, have not repeated the Wairakei pattern. Subsidence is a solved engineering problem on new projects and a legacy liability on a handful of old ones.
Are geothermal heat pumps environmentally friendly?
Geothermal heat pumps are a different technology from geothermal power plants, and their impacts are much smaller. A ground-source heat pump moves heat rather than generating electricity, using shallow loops a few hundred feet down instead of production wells thousands of feet deep. The EPA estimates they cut energy consumption by up to 44% against an air-source heat pump and up to 72% against conventional electric heating and cooling.
Their environmental issues are narrow and manageable. Closed-loop systems circulate an antifreeze mixture, usually propylene or ethylene glycol, which is biodegradable but still a contamination concern if a loop leaks near an aquifer. Open-loop systems draw and return groundwater, which can shift local groundwater temperature and chemistry. Refrigerant accounts for roughly 16% of a system’s lifetime CO2 footprint. Most jurisdictions impose minimum setbacks from wells and wellhead protection areas for exactly these reasons.
What are the environmental trade-offs at a glance?
| Environmental benefit | Environmental cost |
|---|---|
| Life-cycle emissions of 38 to 76 g CO2e/kWh, roughly 6 to 26 times lower than coal | High-gas reservoirs can reach 341 g CO2e/kWh, near gas-plant territory |
| Smallest land footprint of any renewable per terawatt-hour | Sited in volcanic and geologically sensitive terrain that is often protected |
| Air-cooled plants use under 200 gal/MWh, well below coal or nuclear | Water-cooled plants can reach 5,000 gal/MWh |
| Runs around the clock, so it needs no gas backup or battery storage | Injection can trigger earthquakes; Pohang 2017 reached magnitude 5.5 |
| Modern fields reinject fluid, preventing subsidence and contamination | Legacy fields without reinjection subsided; Wairakei dropped ~14 m |
| Plants last decades and the resource replenishes with proper management | Upfront cost of roughly $4,000 to $6,000 per kW, with drilling risk before any revenue |
How is enhanced geothermal changing the picture in 2026?
The old objection that geothermal only works in a few volcanic hotspots is weakening. Enhanced geothermal systems, also called hot dry rock geothermal, create permeability in hot rock that lacks natural fluid pathways, using horizontal drilling and fracturing techniques imported from oil and gas. That opens the resource to regions with no surface expression of heat at all.
The scale test is under construction now. Fervo Energy’s Cape Station in southwest Utah is the largest enhanced geothermal development in the world, with 500 MW of capacity fully contracted, including what were the largest geothermal power purchase agreements ever signed when Southern California Edison committed in June 2024. First power is scheduled for 2026, with roughly 70 MW online that year and the balance by 2028, backed by $421 million in non-recourse project financing closed in March 2026. Data-center operators chasing round-the-clock carbon-free power are a large part of the demand, which is also why energy storage and firm clean generation are being bid against each other for the same contracts.
The context for all of this is how small geothermal still is. Worldwide installed capacity sits above 16 GW across 26 countries, producing roughly 95 TWh a year. The United States leads with about 3.97 GW of nameplate capacity as of 2024, up 8% from 3.67 GW in 2020, and geothermal supplies well under 1% of U.S. electricity generation. The environmental question is therefore not whether geothermal is cleaner than the grid it would displace, because it clearly is, but whether the seismic and siting risks can be managed as enhanced geothermal scales into places that have never hosted a plant.
Does the environmental record make geothermal a good investment?
The environmental profile is a reason geothermal keeps winning long-dated contracts, not a reason any particular stock or fund will perform. Firm, round-the-clock carbon-free generation is scarce, which is why utilities and data-center buyers pay for it. That is a demand argument, not a valuation argument.
The risks that show up in this page’s environmental sections show up again on the balance sheet. Drilling costs roughly $4,000 to $6,000 per kW and is spent before anyone knows whether a well produces. A seismic event can stop a project outright, as Basel did. Permitting in geologically sensitive terrain is slow. Investors looking at the sector generally reach it through broader renewable energy funds rather than pure-play geothermal names, of which there are few. This is not financial advice, and anyone considering the sector should do their own research or speak with a licensed financial advisor.
How we researched this guide
Emissions and land-use figures come from NREL life-cycle harmonization work, the World Bank’s review of greenhouse gases from geothermal power production, the Union of Concerned Scientists, and the New Zealand Geothermal Association. Seismicity figures come from the published record on the Basel 2006 and Pohang 2017 events and from peer-reviewed catalogs of The Geysers. Subsidence data comes from published Wairakei-Tauhara monitoring. Capacity and project figures come from U.S. Department of Energy market reporting and company announcements. Where sources disagree, this page gives the range rather than a single number, and every figure is dated. Ranges reflect real variation between plant types, not uncertainty in the underlying measurement.
Last updated July 2026. This revision corrected an earlier claim that geothermal plants use more land than other generation sources, which is the reverse of the measured data; replaced the statement that hydrothermal plants are “completely benign” with the measured emissions, subsidence, and seismicity record; and added the induced-seismicity section, which the previous version omitted. Any investing discussion here is for informational purposes only and is not financial advice.
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