I don't think it's up to the "better" people to solve this problem. Our genetics and culture both evolve much less slowly than technology, and power accumulates via capital concentration much faster than via common-good consensus-building. Also, the kind of rational people we're talking about here often arise as a product of industrialized society and educational systems & cultures of knowledge. Those are the same societies that often have an outsized impact on global inequalities and climate change. If sustainability is the goal, human intellect is what got us away from it and into trouble to begin with -- not that sustainability without what we call intelligent life would be considered worthwhile, by our standards.

Anyhow. You take a paleolithic ape and give it godlike powers with medieval morality, then increase their population eightfold in <200 years... it's gonna be a shitshow. All the resource-consuming things (breeding, extraction, production, warfare) scale up much better than the forces of restraint (academia, law, treaties, philosophy, self-reflection, etc.). It would happen to any species given such a sudden surge in power without planning, and we are not altogether different enough from our ancestors to prevent this.

I think the "rational" people would do what little they can, if only to fill the time and provide some inkling of hope, but doing so under the assumption that the future is already lost. It's too late for a reversal that doesn't involve billions of people and animals perishing.