If my aim is to make a positive impact on the emerging climate crisis, the least productive possible use of my time is spending 5-6 years in the U.S. doing a PhD in political science or international relations.
It could be argued that the best use would be getting an engineering degree. Then, I could either (a) contribute more intelligently to policy, by better understanding the physical dynamics of what we’re dealing with or (b) actually go off and try and build a better battery / solar panel / electricity grid.
Conversely, it could be argued that high-level direction is what is needed, serving to get more specific forms of expertise applied to a sufficient degree. Even if that contention is accepted, however, it seems unlikely that an additional degree in a social science would help.