If use of the power-hungry digital currency bitcoin grows rapidly in the coming years, its emissions could significantly accelerate global climate change, according to an analysis published today (October 29) in Nature Climate Change

Critics say the study is flawed, and its problems include ignoring likely future energy-efficient advances in how bitcoin operates.

It’s well known that bitcoin and similar digital currencies have high energy demands. Bitcoin has no central banking authority, and transactions are instead verified by “miners” through a computationally demanding process. “Bitcoin is a cryptocurrency with heavy hardware requirements, and this obviously translates into large electricity demands,” says study coauthor Randi Rollins of the University of Hawaii at Manoa in a press release

Rollins and her colleagues estimated that the use of bitcoins in the year 2017 emitted 69 million metric tons of CO2. They also used the...

“We don’t have a single thing–not agriculture, not transportation–that we can think of that in two decades would be enough to warm the planet by two degrees. But Bitcoin can,” lead author Camilo Mora of the University of Hawaii tells Forbes.

David Malone, a lecturer at Maynooth University in Ireland who was not involved in the study, writes in an email to The Washington Post that extrapolating from the rates of adoption for other technologies is “speculative, but not unreasonable.” But he adds that technical challenges “might limit Bitcoin’s growth, and so limit the growth in CO2 emissions.”

“While the future growth of cryptocurrencies like bitcoin is highly unpredictable, we do know that the global electric power sector is decarbonizing and that information technologies—including cryptocurrency mining rigs—are becoming much more energy efficient,” writes Eric Masanet, a sustainability and climate change researcher at Northwestern University, in a statement emailed to The Scientist. “It appears the authors have overlooked these two latter trends in their projections, while simultaneously insisting on tremendous growth in cryptocurrency adoption, resulting in inflated and dubious estimates of future carbon emissions.”

Making such changes is part of the point, Mora tells the Post. “This is a good time for the people who have the power to operate these things to be aware of this potential threat that bitcoin is having. . . . And they have choices that are viable to reduce those emissions considerably right now.”

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