Earth models can predict the planet’s future but not their own

I n the 1960s, meteorologist Edward Lorenz was running weather simulations on an early computer system when he realized that a small rounding difference led to extremely divergent weather predictions. He later called this idea the butterfly effect to communicate that small changes in initial conditions, like a butterfly flapping its wings in Nepal, could produce wildly different outcomes, like rain in New York.

But better understanding those initial conditions and how the biological world couples with the atmospheric one can provide better predictions about the future of the planet—from where umbrellas may be most needed in a given season to where electricity needs might sap the grid.

Today, computers are much more powerful than when Lorenz was working, and scientists use a special ki