Check out the NASA/GISS climate model source code here: Should we bet $45 trillion that this code flawlessly represents Earth's actual climate?

modelE Browser

NASA GISS: GISS GCM ModelE

The latest incarnation of the GISS series of coupled atmosphere-ocean models is now available. Called ModelE, it is a complete rewrite of Model II' physics, combined with greater flexibility and more options. These include better representations of the stratosphere, tracer components and various ocean models.
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F90 Code Viewer

The source code corresponding to the basic configuration of ModelE1 can be seen in it's entirety using the f90t0html software package. This allows you to jump around the code in a very intuitive graphical interface. Feel free to notify us of any errors you might find!