  The carbon footprint of Bitcoin has drawn wide attention, but Bitcoin's
long-term impact on the climate remains uncertain. Here we present a framework
to overcome uncertainties in previous estimates and project Bitcoin's
electricity consumption and carbon footprint in the long term. If we assume
Bitcoin's market capitalization grows in line with the one of gold, we find
that the annual electricity consumption of Bitcoin may increase from 60 to 400
TWh between 2020 and 2100. The future carbon footprint of Bitcoin strongly
depends on the decarbonization pathway of the electricity sector. If the
electricity sector achieves carbon neutrality by 2050, Bitcoin's carbon
footprint has peaked already. However, in the business-as-usual scenario,
emissions sum up to 2 gigatons until 2100, an amount comparable to 7% of global
emissions in 2019. The Bitcoin price spike at the end of 2020 shows, however,
that progressive development of market capitalization could yield an
electricity consumption of more than 100 TWh already in 2021, and lead to
cumulative emissions of over 5 gigatons by 2100. Therefore, we also discuss
policy instruments to reduce Bitcoin's future carbon footprint.
