Laboratory, analytical, and simulation studies suggest that Martian dust clouds can become significantly charged via dust/dust contact electrification. If moderate-size dust clouds on Mars are like their terrestrial counterparts, they are expected to have the capacity to create electric fields in excess of 1 kV/m. As on Earth, there is an expectation that these storm-generated electric fields terminate into both the ground and the ionosphere, coupling directly to the capacitor created by these bounding surfaces. Such charged dust storms are expected to drive ionospheric and ground currents, which complete their current path through the fairweather atmosphere remote from the storm. This system forms a Martian atmospheric electric circuit analogous (but not identical) to that created in the terrestrial atmosphere via thunderstorms. Here we define the requirements on Martian dust storms and the surrounding environment to create such a global electric circuit and then model the system. We find that the variation in global electric field is a strong function of Martian season, with possible values ranging in excess of hundreds of volts per meter in the active storm season (southern summer) to less than a volt per meter during the nonstorm season. ¿ 2001 American Geophysical Union