Bitcoin relies on computers, which rely on electricity, to exist.
As the value of bitcoin goes up, the puzzles become increasingly more difficult, and it requires more computer power to solve them.
A 2019 study by researchers at the Technical University of Munich and the Massachusetts Institute of Technology concluded that, in late 2018, the entire bitcoin network was responsible for up to 22.9 million tons of CO2 per year — similar to a large Western city or an entire developing country like Sri Lanka.