You know, compared to any miles you can ride instead of driving, arguing over the eco-friendliness of various frame materials really is marginal gains, IMO. Coming from a guy who burns a wood stove and also has an 8kW solar array on his roof. Aside from that, I follow some people on Strava that have close to 100,000 miles on their carbon race bikes.

I'm going to go ahead and say I bet that the various aluminum bearing surfaces molded into the headtube or BB may even wear faster than you would have to start worrying about fatiguing the frame, on a quality carbon frame. The cheaper, no name lay ups, maybe, I'd be more wary of.