What do you think about using reclaimed timber for construction? Would this save money? Would it reduce tree cutting and reduce global warming and water pollution caused by clear cutting?
From what little I know about reclaimed timber, it has a special niche in the market due to the 'story.' As far as costs go though, I doubt you would save money given the low costs of structural lumber. In fact, forest landowners I know that have sawn their own logs to build an outbuilding, for example, have told me that they did it primarily for the satisfaction of using their own wood; it would have been cheaper to buy the lumber at the local home center when you account for all the costs. And one of those costs is related to local building code requirements that the wood be grade-stamped. If you're talking about using reclaimed lumber for appearance purposes (e.g., flooring, siding, wainscoting, etc.) then it probably doesn't matter. But to reuse the lumber for structural members, I suspect it would need to be graded by a lumber grader, unless it already has a visible grade stamp on it.
On the idea of reducing tree cutting - given the enormous volumes of wood we use to build new structures and remodel existing structures, I don't suspect that using reclaimed lumber would have any significant impact on timber harvesting. In fact, if we are doing a good job of designing and maintaining structures for longevity, there should be less and less wood available to reclaim, right? That said, since reclaimed timber falls into the 'reuse' category of the 'reduce, reuse, recycle' ethic and therefore it's a great idea where feasible.
Regarding global warming, what little I know about the subject suggests we want to use wood in such a way that we sequester carbon for as long as possible - so yes, I'd say reclaiming wood to reuse it as well as ensuring our wood-based structures last as long as possible are steps we can take to address global warming.
On the last topic of water quality, see an article from one of my colleagues: Dr. Paul Adams Responds to Oregonian Water Quality Story.