Historical Development of Climate Models

Early Models

As developed in the early 1920s, the first proper model of climate-related events was a mathematical technique used for numerical weather prediction. This model treated a local weather area as a grid of cells. Using a set of basic equations, the model could, in principle, calculate how differences in pressure between adjacent cells determined wind speed and direction across the represented weather area. Lewis Fry Richardson, a pioneer of numerical weather prediction, attempted to apply the model to actual weather conditions. Richardson's attempt was unsuccessful because he was unable to perform calculations faster than the weather occurred.

During the late 1940s and early 1950s, computers were developed that could reliably perform complex calculations much faster than human beings. American meteorologists used computers to build models [Page 504]of weather simulation, one of the earliest of which was run on a computer named ENIAC. This particular model divided North America into a grid of cells. Taking the known weather conditions for each grid, the model calculated how air should move across the cells. When compared to the real weather that emerged, the model proved partially accurate, though the applicability of the model was limited by computational capacity and scientific knowledge of weather and climate processes.

As scientists developed more successful weather models, scientific focus expanded during the 1950s and early 1960s to include the development of simple climate models. In the earliest of these models designers analyzed the effects of geography and topography of mountain ranges on airflow across North America. They also simulated how energy and momentum moved through the atmosphere, and were able to predict wind patterns with some accuracy. Additionally, simple models began to represent equilibrium in the atmosphere by incorporating calculations for balancing incoming solar radiation with outgoing radiation reflected from the Earth. By the mid-1960s, these developments gave some degree of credibility to climate modeling; models could now simulate coarse processes of the Earths atmosphere.

General Circulation Models

In the late 1960s and early 1970s, computers advanced to the point of performing complex calculations in short timescales. Better observational data and measurements were made available through satellites and ground measurements. These conditions facilitated the emergence of three-dimensional atmospheric general circulation models, which represented climate as a comprehensive system. As they developed, general circulation models treated the atmosphere as layers and incorporated processes of convection, evaporation, and rainfall. The models could simulate the transfer of radiation vertically through the atmosphere, the reflectivity of sunlight from snow and ice, and basic seasonal changes. During this period, oceans were represented in models and coupled with the atmosphere, though these early models treated the ocean as a slab, without any unique dynamics of its own. General circulation models permitted analysis of how the movement of radiation through the atmosphere was affected by water vapor and CO2.

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