True north is on the move. What if the earth tilts further and further till Antarctica is close to the equator and warms up again.
True north moves because the earth wobbles slightly on its axis. There is little danger of further tilt without a very significant event occuring (moon shifting its orbit significantly, meteor impact etc). If Antarctica does move anywhere it will be due to continental drift/tectonic plate activity. http://en.wikipedia.org/wiki/Earth
The angle of the Earth's tilt is relatively stable over long periods of time. The tilt does undergo nutation; a slight, irregular motion with a main period of 18.6 years. The orientation (rather than the angle) of the Earth's axis also changes over time, precessing around in a complete circle over each 25,800 year cycle; this precession is the reason for the difference between a sidereal year and a tropical year. Both of these motions are caused by the varying attraction of the Sun and Moon on the Earth's equatorial bulge. From the perspective of the Earth, the poles also migrate a few meters across the surface. This polar motion has multiple, cyclical components, which collectively are termed quasiperiodic motion. In addition to an annual component to this motion, there is a 14-month cycle called the Chandler wobble. The rotational velocity of the Earth also varies in a phenomenon known as length of day variation.