Question

Why link Romer and Nordhaus in one Nobel Prize?

Answer 1

Well, the official reason is that "[t]his year’s Laureates have designed methods for addressing some of our time’s most basic and pressing questions about how we create long-term sustained and sustainable economic growth." If you want to learn details about the nomination and selection process, you need to wait for 50 years. I'm not sure what other answers you would expect.

Comments

Maybe I should rephrase the question:

Is there any good argument for linking Romer and Nordhaus in one Nobel Prize?

   At EJMR someone made a good observation: absolutely nobody in discussions predicted that they would be joint winners, which is a good indication that their work  is entirely unrelated.

Answer 2

Joshua Gans takes a shot at channeling the Nobel economics committee here: https://digitopoly.org/2018/10/08/a-nobel-prize-for-breaking-through-hurdles-placed-by-economists/

Comments

Gans: "They were present in every, single policy discussion and tipped the balance towards action in cases where there were significant barriers and hurdles. In so doing, each showed how a careful accounting of economic forces can lead to progress, reduce uncertainty and make the case. That is what ties these two together..."
        That's just  polite, high school English concluding paragraph stuff.  Yes, what they did had policy implications and actually affected policy.  That's not linkage.