These computers, often called “rigs,” are purpose-built. Able to withstand dramatic shifts in temperature and humidity, they are singularly programmed not only to perform just one computation trillions of times each second, but to repeat those computations around the clock and without pause. They are also energy hogs: the 7,000 in Saint-Hyacinthe alone consistently draw more energy than the Montreal Canadiens’ nearby hockey arena, even on a sold-out game night.

Globally, millions of these computers are in operation, part of the cryptocurrency boom that began in 2009. In the decade since the inception of Bitcoin, most of this mining work has occurred in countries like China and Romania, which offer plentiful electricity and little regulation. In 2016, Hydro-Québec announced a formal plan to woo data centers like those run by Microsoft and Amazon. Cryptocurrency miners also came calling, and began submitting proposals in September 2017. Interest from them soon became overwhelming, with more requests than the power company could accommodate. Were Quebec to accept even a fraction of them, the province could well become the new global hub of cryptocurrency mining. That has raised questions about how well Hydro-Québec’s grid can sustain these energy demands, particularly in the winter. Meanwhile, environmentalists and social-justice advocates worry about the ecological and cultural impact of this campaign. And that, in turn, raises difficult ethical questions about the real value of a wholly virtual currency.

Worthless puzzles

Cryptocurrencies are energy-intensive by their very nature. As decentralized ledger systems, of which Bitcoin is the largest, most rely for their security on an approach known as “proof of work.” About every 10 minutes, Bitcoin releases new currency in exchange for successfully solving computational problems that verify a “block” of transactions. Participants do this by converting the data representing those transactions into a sequence of code known as a “hash,” trying again and again until they arrive at one that meets certain criteria. And while it doesn’t require an immense degree of sophistication—insiders liken the process to guessing lottery numbers—it does require an immense quantity of wrong guesses.

“You’re essentially solving worthless puzzles that we cannot solve mathematically,” says Christian Catalini, associate professor of technological innovation at MIT and founder of the university’s Crypto­economics Lab. “You can only brute-force your way into it.” And the muscle behind that force comes in the form of electricity used to power miners’ computers.

Resource intensiveness is inherent in a decentralized system like Bitcoin’s, says Catalini, because it is based on a fundamental lack of trust between participants. Instead of being guaranteed by a central bank like, say, the US Federal Reserve, cryptocurrencies like Bitcoin combat fraud by making all transactions transparent and verifiable by all participants. Attempts to tamper with such a ledger must be made self-defeating.

“Basically, you’re placing an economic cost between a user and an attacker,” says Catalini. “If someone wants to subvert the system by faking a transaction, or revert a legitimate transaction, they would have to expend a tremendously high amount of energy and computation—to the point that no rational economic actor would do that, because the cost of doing an attack would be far greater than the benefit.”

But that means legitimate transactions must also expend extensive energy to prove their validity.

David Malone is a senior lecturer at Ireland’s Maynooth University, where he specializes in the mathematical modeling of network systems. The current global Bitcoin hash rate, which is to say the total number of mining computations, is approximately 25,000,000,000,000,000,000 per second, or 25 million terahashes a second. That’s an increase from 300,000 terahashes a second just four years ago, and the figure is expected to continue growing in the months and years to come. Factor in additional energy consumption required to cool the computers (they can’t function in temperatures over 40 °C), and Malone estimates that Bitcoin alone is consuming as much electricity as the entire nation of Ireland at any given moment. And while Bitcoin is the largest proof-of-work cryptocurrency, it’s far from the only game in town: at last count, there were nearly 1,500 in operation, each with its own energy demands.