Texas was gasping for electricity. Winter Storm Uri had knocked out power plants across the state, leaving tens of thousands of homes in icy darkness. By the end of Feb. 14, 2021, nearly 40 people had died, some from the freezing cold.

Meanwhile, in the husk of a onetime aluminum smelting plant an hour outside of Austin, row upon row of computers were using enough electricity to power about 6,500 homes as they raced to earn Bitcoin, the world’s largest cryptocurrency.

The computers were performing trillions of calculations per second, hunting for an elusive combination of numbers that Bitcoin’s algorithm would accept. About every 10 minutes, a computer somewhere guesses correctly and wins a small number of Bitcoins worth, in recent weeks, about $170,000. Anyone can try, but to make a business of it can require as much electricity as a small city.

In Texas, the computers kept running until just after midnight. Then the state’s power grid operator ordered them shut off, under an agreement that allowed it to do so if the system was about to fail. In return, it began paying the Bitcoin company, Bitdeer, an average of $175,000 an hour to keep the computers offline. Over the next four days, Bitdeer would make more than $18 million for not operating, from fees ultimately paid by Texans who had endured the storm.

Ninety-two percent of the power demand of the Genesis Digital Assets mine in Pyote, Texas, is met by fossil fuel plants, causing 546,000 tons of carbon pollution each year.

Aerial view showing ten large buildings next to rows of smaller structures surrounded by dirt and sparse plants.

All 34 Bitcoin Mines and the Emissions They Cause

The nonprofit tech company WattTime used data provided by The Times to calculate how much of the additional electric generation the operations required was met by fossil fuel plants, and the carbon emissions that resulted.

Source: WattTime analysis, New York Times research Power levels are as of March 9 and based on information from each company or its most recent prior public statement. Fossil fuel percentages do not include energy imported from other states, the type of which is unknown; that results in low numbers for the Merkle Standard mine in Usk, Wash., and the Atlas Power mine in Butte, Mont.

Ninety-nine percent of the power demand of the Stronghold Digital Mining operation in Nesquehoning, Pa., is met by fossil fuel plants, causing 192,000 tons of carbon pollution each year.

Aerial view showing rows of buildings within three cleared areas surrounded by green grass and trees.

Ninety-two percent of the power demand of the Core Scientific mine in Denton, Texas, is met by fossil fuel plants, causing 501,000 tons of carbon pollution each year.

Aerial view showing a building complex with rows of large structures surrounded by brown ground and green plants.

Ninety-two percent of the power demand of the Galaxy mine in Afton, Texas, is met by fossil fuel plants, causing 400,000 tons of carbon pollution each year.

Aerial view showing a large building with a white roof and rows of attached rectangular structures surrounded by dirt.