i had this same problem with a sapphire 7950. it would jack right up to 100 within five minutes of mining. all the other cards on the mobo were an acceptable 78 degrees. i rma'd it and got back a card that can't mine for S*** so now im dealing with that. boy o mining is fun!
What software are you using to mine? You can adjust the temperature of work with some software like CGMiner or BFGMiner.
My rig is using two USB fans to help and my working temperature is always 70 degrees
If you have a big fridge, put your rig inside. Hahaha!!