Wood, coal, gas and oil have long-fueled societies since prehistoric times but they all emit carbon dioxide and all are finite. Today, rapid economic growth is straining the Earth’s ability to meet demand for these fuels, and rising greenhouse-gas concentrations are threatening the climate’s stability. Clean, renewable energy alternatives are being proposed to replace these fuels, but many have limitations: Wind may not blow when demand is up, the sun shines only part of the day and drought can cripple a hydropower plant. Because fossil fuels are still abundant and relatively cheap, they will continue to provide the bulk of
The 2016 Summer Olympics boating and swimming events have put an international spotlight on what has been a long-running problem in Rio de Janeiro—untreated sewage and trash are clogging up major bays and waterways.