The "I have not heard from him since." was kind of cryptic. How long ago was this? And have you written back since?

Tim

tim, sorry, should have been more clear. we were in the habit of corresponding at least a few times a year up until that exchange. no, i have not written back since, as the tone of his email seemed clear to me ("not interested in discussing this issue further"). several months to a year would not have been unusual to pass, but 3 years is. in the past he has been more than interested & willing to discuss his geology projects and views with me. this just came across to me in two ways: "oh no, my buddy has been caught up in this crackpot idea of peak oil" and/or "this is something i don't want to be caught dead expressing an opinion on"

Then just call him up and see if you can buy him lunch. Couldn't hurt.