ENSO blogger Tony Barnston explains why climate forecasters can't get by with just a single indicator for predicting El Niño and La Niña.

The forecasts often provided useful information for the coming few months, but had more limited accuracy and value in forecasting beyond that.

 We’d like our forecasts—both weather and climate—to be simple and certain. Because of the fluid and chaotic nature of the ocean and atmosphere, however, forecasts are never about certainty: they’re about probability.

ENSO arises from changes across the tropical Pacific Ocean. So why does ENSO affect the climate over sizable portions of the globe, including some regions far removed from the tropical Pacific Ocean?