Sorry FROMAIBTOBOEING, I have to disagree ;-)
VMCG and VMCA are the minimum speeds on ground/in the air, where the airplane can be controlled with the most critical (in terms of yaw-momentum) engine inoperative by aerodynamic means (i.e. rudder) only.
Thus, VMCG and VMCA behave similar to the installed takeoff thrust of the engine:
with increasing OAT, VMCG/VMCA get lower (thrust gets lower)
with increasing PA, VMCG/VMCA get lower (thrust gets lower)
However, this is not linear. Typcial jet engines are flat rated up to a certain "break point" temperature (e.g. ISA+15-17) and above that they are full rated, with the thrust rapidly decreasing over temperature. With increasing PA this curve shape is moved towards less thrust.
Typical example would be:
oft, VMCG 126kts up to 30degC, then falling to 112kt at 54degC
10000ft, VMCG 111kt up to 10degC, then falling to 100kt at 35degC
There is an additional restriction for VMCA concerning VStall (VMCA <= 1.2xVStall) but I'm not sure about the exact number.
On some airplanes VMCG might also change with bleed settings (A/I and A/C) and T/O weight.