Technicians make repairs to bitcoin mining machines at a mining facility operated by Bitmain in Ordos, Inner Mongolia, China, on Friday, Aug. 11, 2017. Qilai Shen | Bloomberg | Getty Images China could end up exceeding its emissions reduction targets as a result of carbon-intensive bitcoin mining, according to a study published this week. Some 75% of the world's bitcoin mining is done in China, where there is cheap electricity and relatively easy access to manufacturers who make specialized hardware, according to the study. As a result, the nation's bitcoin carbon footprint is as big as one of its ten largest cities, the paper claims. Unlike most forms of currency — issued by a single entity like a central bank — bitcoin is based on a decentralized network and needs to be "mined." This takes place when bitcoin transactions, recorded on a public ledger called the blockchain, are "verified" by miners. These miners run purpose-built computers to solve com