iMac screen fogging up I leave my iMac (24') next to the sliding door in the lounge at night. The door remains open, so the air gets very cold at night. When I turn my computer on in the morning the screen fogs up inside, presumable because of the cold air inside warming up quite suddenly from the heat of the LCD.

Is there an easy fix, or a way to avoid this happening?
Consider the operating temperatures of the iMac and see if you’re not going beyond the limits. Electronics cannot (and shouldn’t) be operated beyond temperature limits. As much as heat is bad, extreme cold is not good either. 

As already suggested, do not expose your iMac to “very cold air at night”.