A brief history of models

CCSM belongs to an elite category of computer-based simulations known as general-circulation models. Such models use mathematical formulas to recreate the chemical and physical processes that drive Earth’s climate. Extraordinarily sophisticated, they incorporate phenomena ranging from the effect that volcanic eruptions have on temperature patterns to the impact of shifting sea ice on sunlight in the atmosphere. What emerges from trillions of computer calculations is a picture of the world’s climate in all its complexity.

Models such as CCSM are vital to climate science because researchers cannot recreate the atmosphere in a test tube and run experiments on it. Instead, since the 1950s, scientists have used increasingly sophisticated computer programs to answer our most fundamental climate questions, such as the impact of El Niño on North American rainfall and the effect industrial pollution has on temperature and precipitation. As they become more powerful, these models eventually will help us predict the likelihood of climate patterns for specific regions or individual states, providing information that government and business leaders can use to protect investments—and even save lives.

Climate modeling has its roots in the 1950s, when meteorologists tracking daily weather turned to the first vacuum-tube computers to try to forecast variables such as temperature, wind, and humidity. As technology advanced, model simulations were carried out for longer time scales, thus giving birth to climate models. Researchers created models using classical physics equations, such as the conservation of momentum and heat, to shed light on the average state of the entire atmosphere over long time periods. The resulting general circulation models, by the 1970s, emerged as a central tool of climate science.

Meanwhile, oceanographers created computer models of their own to simulate general circulation in the oceans. Since ocean currents and temperatures are a major component of the overall climate system, climatologists began "coupling" ocean and atmosphere models in the 1980s.

To mimic climate even more accurately, scientists in the last 15 years or so have turned to increasingly powerful supercomputers to incorporate additional pieces of Earth’s climate system, including sea ice and land. Today’s models represent a staggeringly complex effort to simulate natural events that may occur hourly (large frontal systems), monthly (jet-stream meanders), or even on timescales of decades or centuries (ocean circulation and glacial changes).

Climatologists around the world have created about a dozen fully coupled atmosphere-ocean models. Some of the better known models, in addition to CCSM, have been developed by Britain’s Hadley Centre for Climate Prediction and Research and Germany’s Max Planck Institute for Meteorology.