Mining around the world is noted for its environmental impact: that’s true of Bitcoin mining as well. A new analysis from researchers at MIT and the University of Munich reveals that the computations required to produce this cryptocurrency take as much energy annually as an American city of more than 400,000 people.
Christian Stoll, who studies energy use, and his coauthors aren’t the first to try and calculate the power requirements of cryptocurrency mining, but getting an accurate figure isn’t simple as there are many factors involved. To arrive at a number, the researchers had to learn more about two variables, says Stoll: how much energy the computers that do the actual mining use, and where they’re distributed.
Cryptocurrencies, the best-known of which is Bitcoin, are untraceable digital currency produced using cryptography techniques by a decentralized network of computers. Bitcoin miners use computer hardware to solve numerical puzzles: each solution helps validate the currency and produce Bitcoin for the miners themselves. Over the last few years, as the currency boomed, the number crunching it takes to produce a single Bitcoin has gone up more than four times, and with it, the energy required.
“The key to a reliable estimate of the power demand is the hardware which the miners use to solve these Bitcoin puzzles,” says Stoll. The researchers relied on the information that Bitmain, Canaan, and Ebang, the major producers of Bitcoin mining hardware, had to provide as part of their IPOs as they became publicly traded companies on the stock market. Then they looked at all the different scenarios in which people mine Bitcoin, from single computers to large operations, and figured out how much total power was likely used between an upper and lower threshold of energy-use efficiency.
Total energy use still doesn’t match up directly with emissions, since different methods of energy production produce different quantities of carbon. Mining on a computer powered by solar panels isn’t as carbon-intensive as running the same program on the same device in an area that uses coal. To figure this out, the researchers looked at the IP addresses of the computers, servers, and networks involved in the mining process to find their location.
By looking at the geographic footprint for mining combined with local emissions via energy consumption, and linking that to total energy consumption, the researchers found that Bitcoin mining produces around 22 million metric tons of carbon dioxide annually. That’s close to the output of Kansas City, which has a population of around 489,000. To put that in a global perspective, the authors write, ”the emissions produced by Bitcoin sit between the levels produced by the nations of Jordan and Sri Lanka.”
“You need the localization as a key ingredient to know how dirty or clean the power is that these miners are using,” says Alex de Vries, a Bitcoin expert with PriceWaterhouseCooper who was not involved with the study.
In a way, Bitcoin mining is the ultimate expression of capitalism gone off the rails: an individual miner or a consortium of miners can make mad bank, but it’s coming at the cost of the collective good. “In order to keep global warming below two degrees Celsius—as internationally agreed in Paris COP21—net-zero carbon emissions during the second half of the century are crucial,” the researchers write. This adds to a growing body of work suggesting that we might need crypto regulations “to protect individuals from themselves and others from their actions,” they write.
“Cryptocurrency, I would say, is only the first step,” says Stoll. Blockchain technology is used elsewhere, in things like logistics and even video games. Blockchain is highly secure and can’t be edited or deleted. But given how energy-intensive Bitcoin mining is, Stoll says, it’s worth asking if we should be using it at all.
“There have been some claims floating around that Bitcoin mining is green,” says de Vries. “This paper disproves that.”
Correction: A previous version of this article stated that mining produces around 22 metric tons of carbon dioxide a year when it in fact produces around 22 million metric tons.