I have a GTX460 and it goes wild when outdoors, as well. I fixed the heat, and subsequent noise, issue by undervolting it from the default 0.925v to 0.825v, but I had to do a very slight underclock to keep the GPU stable. Peak temps dropped from ~83C to ~62C and I still get 60 FPS 95% of the time.

As Shokun pointed out, all cards behave differently, so you may get different results undervolting your card. I used MSI Afterburner to undervolt and underclock.