From 1998 to 2012, the Earth’s surface warmed more slowly than expected. Many climate scientists explained that this slowdown was caused by the oceans, which drew heat downward, away from the surface. The authors of a new study question this view: variations in the energy radiated from the surface to space could also have caused the slowdown. Furthermore, the amount of energy required to cause a slowdown is smaller than previously thought. It is in fact considerably smaller than the observational uncertainty, which suggests that the true origin of the recent slowdown may never be discovered.