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What are the different global climate models?

Projecting future climate requires sophisticated computer models. The 2009 Climate Scenarios Project used projections from six global climate models, all of which had been run with two selected emissions scenarios (A2—mid-high; B1—lower). On one hand we have different emission scenarios, on the other we have different models to predict how the environment will react to these scenarios. This is called “climate sensitivity” which depends on Earth’s response to certain physical processes, including a number of “feedbacks” that might amplify or lessen warming.

For example, as heat-trapping emissions cause temperatures to rise, the atmosphere can hold more water vapor, which traps heat and raises temperatures further—a positive feedback. Clouds created by this water vapor could absorb and re-radiate outgoing infrared radiation from Earth’s surface (another positive feedback) or reflect more incoming shortwave radiation from the sun before it reaches Earth’s surface (a negative feedback). Because many of these processes and their feedbacks are not yet fully understood, they are represented somewhat differently in different global climate models. The four global climate models available in Cal-Adapt are:

The grid sizes of these global climate models are very coarse, in the order of 150 by 150 miles (see the graph below). For this reason, there is a need to further “downscale” the results of these global climate models to produce climate scenarios for California at adequate level of geographical resolution (see the California map at the right hand corner below).


Model Uncertainty

The future climate data available, and used within Cal-Adapt, represent a projection of potential future climate scenarios, they are not predictions. These data are meant to illustrate how the climate may change based on a variety of different potential social and economic factors.  A thorough examination of model performance and evaluations can be found in the IPCC's Third Assessment Report.

Post last edited on: 2011 April 13

Tags: background, climate models

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