Stronger El Niño events are more likely when springtime surface waters in the western Pacific Ocean become unusually salty, a new study in Geophysical Research Letters suggests. Traditionally, scientists have focused on temperature and wind patterns to understand El Niño—periodic shifts in the tropical Pacific between warmer and cooler conditions that influence weather patterns across the globe. But researchers now show that subtle variations in ocean salinity north of the equator during boreal spring (March to May) can substantially amplify El Niño's strength and nearly double the odds of an extreme event.