Previous work has established that warming is associated with an
increase in dry static stability, a weakening of the tropical
circulation, and a decrease in the convective mass flux. Using a set of
idealized simulations with specified surface warming and
super-parameterized convection, we find support for these previous
conclusions. We use an energy and mass balance framework to develop a
simple diagnostic that links the fractional area covered by the region
of upward motion to the strength of the mean circulation. We demonstrate
that the diagnostic works well for our idealized simulations, and use it
to understand how changes in tropical ascent area and the strength of
the mean circulation relate to changes in heating in the ascending and
descending regions. We show that the decrease in the strength of the
mean circulation can be explained by the relatively slow rate at which
atmospheric radiative cooling intensifies with warming. In our
simulations, decreases in tropical ascent area are balanced by increases
in non-radiative heating in convective regions. Consistent with previous
work, we find a warming-induced decrease in the mean convective mass
flux. However, when we condition by the sign of the mean vertical
motion, the warming-induced changes in the convective mass flux are
non-monontonic and opposite between the ascending and descending
regions.