Coal has historically been the largest source of global electricity generation. For the first half of the 20th century, more than half of the world’s electricity came from coal power plants. Until the 1950s, most of the rest came from hydroelectric plants. Nuclear power grew rapidly from the 1950s up until a decline that began at the turn of the new century. Natural gas assumed a growing role that has continued to increase since then. Only in the past two decades have renewables like solar and wind power become significant contributors.