How Far Ahead Can We Forecast?

Chaos and the limits of prediction

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• The atmosphere is chaotic: small errors grow exponentially, doubling every couple of days.
• Each halving of the initial error buys only one doubling time, so forecasts are limited to about two weeks.
• Ensembles forecast probabilities; climate projections forecast statistics, not days.

Steps

1. A rounding error
2. Ten days on
3. Buying more days
4. Ensembles
5. Better measurements
6. Weather versus climate