The operators of the only bitcoin mine in Missoula County, Montana, thought they were doing everything right. They set up shop in an abandoned mill on the edge of town, made a plan to recycle the computers when they conked out, and contracted with a nearby dam for cheap renewable power. Sure, it might be a warehouse full of energy-intensive computers and cooling systems, designed to churn out digital money day and night. But it would be a low-carbon, low-impact operation all the same.

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