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Models allow a user to explore a variety of what-if scenarios and the interdependencies of the system under scrutiny

System dynamics modeling tools enable users to experiment with complex systems and recognize the mechanisms that govern dynamic interactions. Several modeling tools are designed specifically to study Earth system science of which Stella and ESMF are the popular ones.

STELLA is a commercial software package for building and simulating models of dynamic systems and processes. Some of the models generated by ESSE21 community using STELLA include the global carbon cycle, Earth energy balance, Darcy tube, short time-scale biosphere, radiative transfer, hydrologic cycle, and nutrient cycle.
Earth System Modeling Framework (ESMF) is a public domain flexible software infrastructure for Earth system studies.
Community Climate System Model (CAM) is a coupled climate model for simulating the earth's climate system and is composed of four separate models.
The MITgcm (MIT General Circulation Model) is a numerical model designed for study of the atmosphere, ocean, and climate. 
EdGCM is an educational implementation of GCM models