QUESTION:
If it were possible to raise the surface temperature of Mars above 0°C,
possibly through the greenhouse effect, what effect would that have on
the thickness of the permafrost?  If a significant portion of the
permafrost
was melted, what effect would that have on the topography of the planet?

ANSWER from Bruce Jakosky on March 29, 1999:
Technically, permafrost is defined as those regions in which the
temperature
never rises above the melting temperature of ice.  In this sense,
raising
the surface temperature to 0 degrees C would have no effect on the
distribution of permafrost near the surface.  At depth, though, where
geothermal heating and conductive loss of heat cause the temperature to
increase, raising the surface temperature would raise the lower boundary
of where permafrost exists; that is, the depth to the bottom of the
permafrost region, which currently is probably 3-6 km below the surface,
would shrink.

We know that there must be (or must have been) a depth at which there is
a
transition from ground ice to groundwater:  The surface is certainly too
cold
for water to exist as a liquid, yet we see compelling geological
evidence that
liquid water was released in catastrophic floods to the surface.

The distribution of ground ice is a complicated function of where ice is
stable today, how water molecules or liquid move around and on what
timescales,
and what the recent history of the distribution of ice has been.  To
date,
there are really only theoretical calculations of where ice is likely to
exist.

A good place to see a detailed discussion of some of these issues is in
Michael Carr's recent book on "Water on Mars", published by Oxford
University
Press.