overheating: is there a way to set temperature thresholds in Ubuntu?

You should not put your laptop in your lap. Your clothes can block the intact vents. You should put your laptop on a cooling pad:

cooling cushion.png

The cooling pad in turn can put it in your lap or on your couch, coffee table, bed, etc.

The ventilators of the laptops are controlled by the manufacturer and are activated at certain temperatures. To prevent your laptop from turning off when it is too hot you can use Intel Powerclamp. You should also be using thermal Y tlp.

See: stop cpu overheating