Can anyone explain why polarizers tend to cool as they polarize?

This is a well known effect, but I've never heard an explanation of what causes it. One interesting thing I've noticed is that if you take a polarizer (in my case a MC Rodenstock) and look through it from the front towards the rear, the polarization is not seen, as the filter is backwards, but you do see the image cool as the filter is rotated towards what would be maximum polarization if looking through in the correct direction (as the film sees). I hope that made sense.... Try it if you don't believe me!

Thank you.