>[!abstract] >The Galton board[^1] can be used as an analog to illustrate the difference between forecasting the weather and forecasting the climate. The inspiration for this comes from [[Tackle, 1995|Tackle (1995)]] (although oddly named the pinball analogy there). > >Each row of pegs, starting from the top, represents one day in a weather forecast. Our confidence in the forecast is reasonably strong after the first day (we have a good idea of where the ball might be past the first row), but it decreases rapidly after each subsequent day/row. Past just a few days/rows, our forecast is effectively useless. > >Climate forecasting, on the other hand, is akin to the distribution of balls at the bottom of the Galton board, after they have passed through an arbitrary large number of rows of pegs. This assumes that the equations in the model (or model ensemble) describe with enough fidelity Earth's climate and boundary conditions (analogous to the elasticity, horizontal position, and shape of the pegs), as well as the initial conditions (analogous to the top ball feeder's characteristics). In this case, each individual ball trajectory only represents a plausible sequence of daily weather, rather than individual day-by-day forecasts. Introducing perturbations such as adding greenhouse gases to the atmosphere is then analogous to adjusting the position or properties of the pegs. ![[includes/assets/notes/galton+board+analogy.jpg]] >[!related] >- **North** (upstream): [[Climate modeling]] >- **West** (similar): — >- **East** (different): — >- **South** (downstream): — [^1]: The Galton board is a device invented to demonstrate the central limit theorem. It consists of a vertical board with interleaved rows of pegs. Beads are dropped from the top and, when the device is level, bounce either left or right as they hit the pegs. Eventually they are collected into bins at the bottom, where the height of bead columns accumulated in the bins approximate a bell curve (Wikipedia, 2025).