From what I have read and watched(never actually applied), if you dig below the frost line, you can accomplish the same thing. While it may be 80 degrees out, 2-3 feet down it could be a cool 30ish degrees. You will have to have some sort of insulating cover for this (such as moss, etc.)
Anyone disagree with this thought?

On a side note, in reference to the previous post by Bob, I used a very large swamp cooler last year while working outdoors at Daytona Bike Week and found it to be a refreshing ally to the humid heat in Florida.