Earth's heat: Impact on nature
Compact and low-carbon, with sinking ground and tremors
Compact and low-carbon, with sinking ground and tremors What this tab covers What taking energy from this source does to land, water, air and climate, wildlife and ecosystems, with life-cycle emissions and land use where measured.Geothermal plants are compact and low-carbon on average, but some reservoirs release large amounts of CO2 and hydrogen sulphide, and fluid extraction or injection can cause subsidence and earthquakes.
Life-cycle emissions 38 (range 6-79) g CO2e/kWh13 Life-cycle, median and range, IPCC AR5 Annex III; individual fields with CO2-rich reservoirs can exceed 1,000 g/kWh Land use about 404 (0.04 ha per GWh) m2 per GWh over 30 years12Effects on nature
| Area | Effect | Size | How it is reduced |
|---|---|---|---|
| Climate (reservoir gases) | Steam carries CO2 from the reservoir; emissions vary enormously by geology10 | Global average about 121 g CO2/kWh; some Turkish fields 400-1,300 g/kWh, comparable to coal | Binary plants that pump and reinject all fluid emit almost nothing; gas capture and reinjection |
| Induced seismicity | Injecting water at high pressure into hot rock can trigger earthquakes11 | Magnitude 5.5 earthquake at Pohang, South Korea, 15 November 2017, hypocentre about 1 km from an enhanced geothermal site | Soft stimulation (stopping injection after small tremors and letting fluid flow back), avoiding stressed faults |
| Subsidence | Withdrawing fluid compacts the reservoir and the ground sinks8 | Wairakei: 15 m after 50 years, rates over 450 mm/yr in the 1970s; Tauhara 2.6 m | Reinjection of spent fluid |
| Air (hydrogen sulphide) | Rotten-egg gas from reservoirs; toxic at high concentration12 | Abatement converts over 99.9% of H2S to elemental sulphur | H2S abatement systems |
| Water | Plants use a little fresh water for cooling; arsenic in the fluid ends up in sludge and scale, boron mostly in condensate that is reinjected12 | About 5 gallons (19 litres) of fresh water per MWh, against 361 gallons for natural gas plants; air-cooled binary plants use none | Reinjection of fluid and condensate, air cooling |
| Land | Well pads, pipelines and plant12 | About 404 m2 per GWh over 30 years, against 3,632 m2 per GWh for coal | Directional drilling from shared pads |
Geothermal's environmental record depends on the reservoir more than on the technology. A binary plant that reinjects all its fluid is close to zero-emission, while a flash plant on a carbonate-rich field can emit as much CO2 per kWh as coal, as measurements in Turkiye show. The two physical risks, subsidence and induced earthquakes, both come from changing the pressure underground, and both are reduced by reinjecting fluid and controlling injection pressure.
Sources
- Update on subsidence at the Wairakei-Tauhara geothermal system, New Zealand USGS Publications Warehouse, 2009
- Greenhouse Gas Emissions from Geothermal Power Production (ESMAP) World Bank, 2016
- Earthquake close to a geothermal site in South Korea GFZ German Research Centre for Geosciences, 2018
- A Guide to Geothermal Energy and the Environment Geothermal Energy Association, 2007
- Climate Change 2014: Mitigation, Annex III Technology-specific cost and performance parameters (Table A.III.2) IPCC Working Group III, 2014