Seasonal climate forecasts: reading tea-leaves in a digital age

Lewis Fry Richardson came up with the idea of numerical weather forecasting in 1922. Back then, his computers were real people in a large room scribbling parts of the calculation on notepads and passing them to messengers and an overall coordinator. A weather forecast starts with Newton’s laws of motion as they apply to gases (the atmosphere) and throws in some basic thermodynamics and the ‘ideal gas’ law. These days, digital computers synthesise millions of observations with Richardson’s mathematical equations on a fine grid covering the entire planet to produce 10-day weather forecasts before morning tea.