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UCAR
What Is a Climate Model?
Global climate models (GCMs) use math - alot of math - to describe how the atmosphere, the oceans, the land, living things, ice, and energy from the Sun affect each other and Earth's climate. Thousands of climate researchers use global climate models to better understand how global changes such as increasing greenhouses gases or decreasing Arctic sea ice will affect the Earth. The models are used to look hundreds of years into the future, so that we can predict how our planet’s climate will likely change.
There are various types of climate models. Some focus on certain things that affect climate such as the atmosphere or the oceans. Models that look at few variables of the climate system may be simple enough to run on a personal computer. Other models take into account many factors of the atmosphere, biosphere, geosphere, hydrosphere, and cryosphere to model the entire Earth system. They take into account the interactions and feedbacks between these different parts of the planet. Earth is a complex place and so many of these models are very complex too. They include so many math calculations that they must be run on supercomputers, which can do the calculations quickly. All climate models must make some assumptions about how the Earth works, but in general, the more complex a model, the more factors it takes into account, and the fewer assumptions it makes. At the National Center for Atmospheric Research (NCAR), researchers work with complex models of the Earth's climate system. Their Community Climate System Model is so complex that it requires about three trillion math calculations to simulate a single day on planet Earth. It can take thousands of hours for the supercomputer to run the model. The model output, typically many gigabytes large, is analyzed by researchers and compared with other model results and with observations and measurement data.
There are currently several other complex global climate models that are used to predict future climatic change. The most robust models are compared by the IPCC (Intergovernmental Panel on Climate Change) as they summarize predictions about future climate change.
