Bitcoin and energy use

We are told that Bitcoin's value is increasing and many people are investing in it... but what is it? and why is it a fairly terrible idea for the planet? It's hard to work out at first reading what this cryptocurrency actually is, and Warren Buffet has said it is essentially worthless, but its impact on the planet is huge through the energy required to keep the currency growing: it relies on endless random number generation.

Read the BBC News article here.