CO2 — Solar power emits no carbon dioxide. However, solar power’s intermittency and unpredictability require other power sources — which often emit significant amounts of carbon dioxide — to back up solar power on a minute-by-minute basis, Accordingly, solar power is a “zero-emissions” power source but is not as effective at reducing carbon dioxide emissions as more reliable zero-emissions power sources such as nuclear and hydro power. Impact: 2

Miscellaneous — Solar power presents the same question as does wind power: Should the “green” or “clean” nature of a power source be measured solely by its air emissions? If so, nuclear and hydro power are equal or superior to wind and solar power. If not, wind and solar power impose environmental harms in other areas that are more severe than many of their competitors. Impact: 2

Geothermal – Environmental Impact: 14

Geothermal power is an expensive source of energy that would produce little if any commercial-scale power without substantial government subsidies. Even with government subsidies, federal auctions for geothermal power rights attract few buyers. Environmentally, geothermal power is a mixed bag of environmental advantages and harms.

Air — Geothermal power can be produced in closed-loop or open-loop facilities. Closed-loop facilities capture and reinject water and toxic pollutants underground. They are also more expensive than open-loop facilities. Closed-loop production emits just a few percent of air pollutants emitted by coal power. Impact: 2

Land — Geothermal power has a significant land impact, requiring 13 acres of land to produce just a single megawatt of power, according to studies. The Union of Concerned Scientists notes “many geothermal sites are located in remote and sensitive ecological areas.” The U.S. Energy Information Administration notes, “Many geothermal features are national treasures.” Impact: 5

Species — Geothermal power entails significant land disruption, often in areas that are remote and ecologically sensitive. This negatively impacts resident plant and animal species. Impact: 3