[halvsjur]

As the first couple of comments on that page says, it's a high chance that this is due to problems with power management in the open-source Radeon driver.

I've been running Debian and Ubuntu on lots of different laptops the last fifteen years, and only ever had problems with overheating on laptops with AMD/ATI graphics and the Radeon driver. If the graphics chip is current enough, installing the proprietary Catalyst driver should fix the problem.