Totting up bitcoin’s environmental costs

AS COINBASE’S IPO shows, cryptocurrencies have many fans. But they have detractors, too. Environmentalists, in particular, fret about how much energy bitcoin uses. In a paper in , a group of academics led by Dabo Guan of Tsinghua University and Shouyang Wang at the Chinese Academy of Sciences examine bitcoin’s energy use in China. They conclude that, in the absence of legal curbs, bitcoin could by 2024 become a “non-negligible” barrier to China’s efforts to decarbonise its economy.Bitcoin’s hunger for energy stems from its design. It forgoes centralised record-keeping in favour of a “blockchain”, a transaction database that is distributed among users. The blockchain is maintained by “miners”, who validate transactions by competing to crack mathematical puzzles with solutions that are hard to find but easy to check. Each successfully mined block of transactions generates a reward, currently 6.25 bitcoins ($357,000).