Re: venting vaulted ceilings
It would help. However, the air leaks you'd add having a operable window or skylights may make it colder and more drafty in winter. I believe your heating season is longer than cooling, so it might ultimately work against you.
For the couple weeks you need AC, a small portable AC unit might not be a bad thing to have. Even a 9000 BTU unit might cool a pretty large area or at least remove a lot of humidity and make it more comfortable.
Global warming... well, lets just leave that topic alone.... lets just say that energy conservation is good policy. Carbon credits and sequestering CO2 in some "Interesting" ways isn't the best use of resources.
1925 Two-Story Stucco Beaux Arts Neoclassical