There was an IEEE paper back in 2006 that estimated Blu-Rays as having a life expectancy over 50 years in the Amazon, 200 years in Montreal, 500 years in Osaka, 1000 years in a typical office environment, and 2000 years in Montreal based on temperature and humidity. Whether it is a normal Blu-Ray or a special archival one, I don't know. The title is "Over 500 Years Lifetime Dual-layer Blu-ray Disc Recordable based on Te-O-Pd Recording Material" by Naoyasu Miyagawa, Hideki Kitaura, Katsuyuki Takahashi, Yukako Doi, Haruhiko Habuta, Shigeru Furumiya, Ken’ichi Nishiuchi and Noboru Yamada.

I'm not sure if it is just a marketing piece or what, but it was presented at the Optical Data Storage Topical Meeting in 2006.