First off I have to state that I fit more in the catastrophists camp (with reservations) than the optimists one. Minor institutional reforms and incremental technological fixes will not, in my opinion, add up to sustainability. Best case projections by scientists in relevant fields who are not on the payroll of energy, auto, etc are far from promising. We are more closely aligning to worst case scenarios as far as we can tell with the currently available data. Predictions about the number of years before any specific catastrophe are generally bound to be wrong. Forty years or eighty years; it doesn't matter. I don't believe it is probable that the necessary changes to prevent an environmental catastrophe will come about in time. I doubt it will mean the extinction of our species however. No one can know which cause will give the greatest "bang for the buck" so to speak in bringing about change. We can assume that some will be more effective than others and simply focus our energies on those. Will fighting for the rights of same-sex couples to marry have a direct effect on anthropomophic climate change? Probably not, but you're unlikely to find many people fighting for this cause to the exclusion of all others. Pick a decent battle and fight it.
John Thornton