Environmentalists have an above-ground and a below-ground view of the world. Energy sources harnessed on or close to the surface, like wind, wave, tidal, solar and hydropower, are good. They are renewable and do not emit carbon dioxide, the main greenhouse gas from human activity warming the planet.
However, energy sources found under the ground, such as the fossil fuel trio (coal, oil and natural gas), and uranium used for nuclear power, are bad.
Fossil fuels are major greenhouse gas emitters while nuclear power, although it produces almost no global warming emissions, is still regarded by many environmentalists as too much of a safety and proliferation risk.
Yet there is another form of underground energy gaining prominence as a future source of power that gets an environmental seal of approval: geothermal heat. What comes out of the ground with this form of energy are hot water and steam, and almost no pollution.
Advocates point out that geothermal is currently the only renewable energy that provides a near-constant supply of base-load electricity to commercial grids in the same way that plants powered by coal, oil, gas and nuclear fuel do.
Other types of renewable energy generate electricity intermittently, depending on the strength of the sun, wind, waves and tides. But they seem unlikely to match geothermal power in cutting greenhouse gas emissions and changing the way electricity is generated.
Southeast Asia is a world leader in exploiting the first wave of geothermal power, although it could do even more with the right incentives.