An overview

CCSM, run on some of the world’s most powerful supercomputers, simulates the many interconnected events that drive Earth’s climate. These include changes in the atmosphere and oceans, the ebb and flow of sea ice, and the subtle impacts of forests and rivers.

CCSM is unique among powerful models. Funded by the National Science Foundation and the Department of Energy, it belongs to the entire community of climate scientists, rather than to a single institution. The hundreds of specialists at various institutions in the United States and overseas who collaborate on improvements to CCSM make the model’s underlying computer code freely available on the Web. As a result, scientists throughout the world can use CCSM for their climate experiments.

Scientists unveiled the first version of CCSM in 1998. CCSM-2, the version released in 2002 and constantly updated, represents a major advance because it contains far more information about Earth’s physical processes. For example, it tracks the flow of major rivers that empty into the oceans and influence currents such as the Gulf Stream. It contains up to five characteristics of sea ice within each grid cell, such as the thickness and the melt rate. And the fine scale of its resolution allows scientists to capture significantly greater detail about ocean currents and the mixing of salt and fresh water.

CCSM-2 recreates climate by dividing the world’s water and land surface into rectangular grid points that extend upward into the atmosphere in 26 vertical layers. Its resolution varies from 2.8 degrees longitude by 2.8 degrees latitude to an even finer resolution, for oceans and sea ice, of 1 degree by 1 degree–meaning that each cell of the grid at peak resolution corresponds to approximately 10,000 square kilometers (about 3,900 square miles).

For every grid point, the model uses equations to solve such physical processes as the formation of clouds and the movement of heat and moisture. Scientists also input chemical components such as ozone and carbon dioxide that can affect cloud formation or trap solar heat.

Such complex calculations demand an extraordinary amount of computer power. To recreate a single day of the world’s climate, the model must perform 700 billion calculations. Although this means producing a picture of the atmosphere takes a long time, the payoff is that CCSM-2 can simulate Earth’s climate patterns in considerable detail.