(Bloomberg) — More than eight years since the birth of bitcoin, central banks around the world are increasingly recognizing the potential upsides and downsides of digital currencies. The guardians of the global economy have two sets of issues to address. First is what to do, if anything, about the emergence and growth of the private cryptocurrencies that are grabbing more and more attention — with bitcoin now sitting above $16,000 and futures trading this week heralding a new level of mainstream acceptance.