Quantitative estimations of the global circuit parameters have been made to test the terrestrial and/or extraterrestrial controls of the global atmospheric electric circuit. A global model of electrical conductivity in the lower atmosphere between 0 and 60 km was constructed first. In this model we consider the ionization caused by cosmic rays and radioactive substances and attachment of ions to condensation nuclei or cloud particles. The responses of the atmospheric electrical parameters to the variations of the cosmic ray ionization and the condensation nuclei concentration were then examined. In the first case, when the cosmic ray ionization decreases by 20%, the ionospheric potential increases by 15%, and the electric fields above the ocean and the continent increase by 20% and 7%, respectively. On the other hand the global current does not increase so much (0.8%), and the air-earth current decreases by 0.7% above the ocean but increases by 3% above the continent. This difference between responses above the ocean and above the continent is caused by the ionization resulting from the radioactive substances over the continent. In the second case, when the condensation nuclei concentration increases by 20%, the ionospheric potential increases by 8%, and the electric field increases in the nonmountain region more than in the high mountain region, while the air-earth current increases obviously in the high mountain region.