Iceland is cold. But it sits atop one of the world’s hottest underground regions, giving the country the ability to tap into a massive store of geothermal energy held by live volcanoes beneath Icelanders’ feet. Drill down only a few hundred meters, and trapped water will come gushing out as high-temperature steam. It’s easy enough to turn that into electricity: just run it through a turbine to drive an electrical generator, like we’ve been doing for over 100 years with any kind of steam.

The only problem is drilling into these volcanic regions also releases carbon dioxide, the major greenhouse gas driving global climate change. Geothermal power is still very clean, producing just 3% of the emissions of a coal plant generating the same power. But Iceland wants to reduce its emissions all the way to zero.

The solution can be found at the Hellisheidi geothermal power plant, Iceland’s largest, just outside the capital Reykjavik. Since 2014, the plant has been extracting heat from underground, capturing the carbon dioxide released in the process, mixing it with water, and injecting it back down beneath the earth, about 700 meters (2,300 ft) deep. The carbon dioxide in the water reacts with the minerals at that depth to form rock, where it stays trapped.

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