Synopsis The Tesla CEO said he worries about “massive use” of coal and other carbon-intensive energy to generate electricity needed to mine digital currency. AFP In February, Tesla said it had purchased $1.5 billion in Bitcoin and planned to accept it as a payment, triggering a rally in its own stock as well as the currency By Chester Dawson Elon Musk stepped up his criticism of Bitcoin as environmentally unsustainable while also signaling support for another digital coin and saying he remains a believer in cryptocurrency. The Tesla Inc. chief executive officer said in a tweet Thursday he worries about “massive use” of coal and other carbon-intensive energy to generate electricity needed to mine digital currency. That followed an earlier Twitter post of a chart from the University of Cambridge showing Bitcoin’s electricity consumption has skyrocketed this year.