Write a summary of the article Geothermal to Heat Buildings.

The ancient Romans used the heat from beneath the Earth's crust to heat buildings and water, but only relatively recently have we begun to rediscover its potential. Under the Ecofys scenario, more than a third of building heat comes from geothermal sources by 2050. This is not restricted to volcanically active areas: direct geothermal heat can provide central heating for buildings in almost all parts of the world.

When temperatures are high enough, geothermal energy can be used to generate electricity and local heating, including high-temperature heat for industrial processes. Unlike wind or solar power, which vary with the weather, geothermal energy provides a constant supply of electricity. Iceland already gets a quarter of its electricity and almost all of its heating from its molten "basement". In the Philippines, geothermal plants generate almost a fifth of total electricity.

Geothermal electric capacity is growing at around 5 per cent each year; the Ecofys analysis suggests we could reasonably hope to at least double this growth rate to provide about 4 per cent of our total electricity in 2050. Geothermal would also provide 5 per cent of our industrial heat needs. Exploiting geothermal resources will undoubtedly affect the surrounding environment and the people who live there. Geothermal steam or hot water used for generating electricity contains toxic compounds, but "closed loop" systems can prevent these from escaping. If sites are well chosen and systems are in place to control emissions, they have little negative environmental impact. In fact, because geothermal plants need healthy water catchment areas, they may actually strengthen efforts to conserve surrounding ecosystems.