The problem is caused by Blizzard trying to improve graphics performance by running the graphics card at full strength, however, something also happened at the same time which limited the detection of the temperature of the GPU and the fan speed control.
This was driving me insane, but I have managed to fix it with two things.
I installed smcFanControl (http://homepage.mac.com/holtmann/eidac/software/software.html), this is a small app that runs in your menu bar of OS X. It allows you to set the speed of your fans. I increased my ODD fan to 2000rpm instead of the default 600.
I also used the following command in WoW.
"/script maxFPS 35"
This sets your maximum fps at 35, which is good enough that I can't see any real difference between this and the 70 I used to get before I started getting the overheating. One side effect of this is when WoW hits the 35fps cap, it actually increases quality a little rather than trying to get the extra fps. I have noticed water translucency and terrain detail are slightly better since I did this.
Fix to WoW graphics glitch introduced in 2.4
This was driving me insane, but I have managed to fix it with two things.
I installed smcFanControl (http://homepage.mac.com/holtmann/eidac/software/software.html), this is a small app that runs in your menu bar of OS X. It allows you to set the speed of your fans. I increased my ODD fan to 2000rpm instead of the default 600.
I also used the following command in WoW.
"/script maxFPS 35"
This sets your maximum fps at 35, which is good enough that I can't see any real difference between this and the 70 I used to get before I started getting the overheating. One side effect of this is when WoW hits the 35fps cap, it actually increases quality a little rather than trying to get the extra fps. I have noticed water translucency and terrain detail are slightly better since I did this.
It is annoying that I needed to fix this with a 3rd party fan speed control program. But it works, and I have not had a problem with it since, even when heavily using Exposé and raiding :D