Reducing greenhouse-gas emissions is not enough to limit global warming to a level that wouldn’t risk young people’s future, according to a new study by a team of scientists who say we need negative emissions. Measures such as reforestation could accomplish much of the needed CO2 removal from the atmosphere, but continued high fossil fuel emissions would demand expensive technological solutions to extract CO2 and prevent dangerous warming. The study is published today in Earth System Dynamics, a journal of the European Geosciences Union.