  We investigate the effect of increased greenhouse gas concentrations on the
zonally averaged location of the jet stream boundary of the polar cell in a
latitude dependent, two-layer Energy Balance Model. The model includes separate
terms for atmospheric and surface albedos, and takes into account reflections
of shortwave radiation between the surface and atmospheric layers. We introduce
the notion of a cloud factor function, which depends on temperature gradients,
to simulate the cell structure of Earth's global atmospheric circulation. A
simulation of increased greenhouse gas concentrations initially results in a
poleward movement of the polar jet stream's mean latitude, but as the
concentration increases the jet moves equatorward. When the model takes both
the atmospheric and the surface temperature gradients into account, under high
concentrations the location of the jet stream becomes unstable and
quasi-periodic as its mean location moves equatorward.
