Bitcoin jumped above US$39,000 after Elon Musk said Tesla would resume transactions with the cryptocurrency when mining is done with more clean energy. The electric car maker will allow bitcoin transactions again “when there’s confirmation of reasonable (~50 per cent) clean energy usage by miners with positive future trend”, Musk, Tesla’s chief executive, said in a tweet. His posting was in reply to a report in Cointelegraph, which cited Magda Wierzycka, executive chair of South African asset manager Sygnia, as saying Musk’s recent tweets on bitcoin should have prompted an investigation by the US Securities and Exchange Commission. This is inaccurate. Tesla only sold ~10% of holdings to confirm BTC could be liquidated easily without moving market. When there’s confirmation of reasonable (~50%) clean energy usage by miners with positive future trend, Tesla will resume allowing Bitcoin transactions. — Elon Musk (@elonmusk) June 13, 2021 The cryptocurrency gained as much as 9.3 per cent to US$39,372 on Sunday afternoon in New York, the highest level since June 3 and just below the US$40,000 round-number level seen as key by some chart watchers. It was down about 1 per cent to US$38,881 as of 7am in Hong Kong on Monday. Musk has whipsawed bitcoin and other digital tokens in the past few months. In February, Tesla announced it had bought US$1.5 billion in bitcoin and signalled its intent to start accepting bitcoin as payment for vehicles. In March, Musk tweeted, “you can now buy a Tesla with bitcoin”, only to say in May that the practice was suspended due to concerns about fossil-fuel usage for bitcoin mining and transactions. The U-turn has been controversial, as Wierzycka’s reported comments indicate, partially because the moves by Tesla and Musk have had noticeable effects on Bitcoin’s price. While there are other issues out there, ranging from institutional adoption and diversification on the positive side to sustainability and regulatory concerns on the negative, a Musk tweet can often change momentum and can dominate the narrative for days or weeks.