This is interesting. A model by Newman et al. (2009) that explores how the stratosphere, and so the solar UV intensity at the earth's surface, would have evolved sans the Montreal Protocol. The idea of actually running through these numbers and publishing them is pretty clever. We take the Protocol for granted but it has been around for so long (1985) that it is also beginning to seem like a 20th century idea. The players have changed. The substances have changed. So the paper has large poltical value.
The paper also shows that there is technical value in modeling what will never be. You can learn new things about a system by watching how a numerical model evolves and responds to changed assumptions and runs off into new parameter spaces. Still this is not a "science" paper in the strict sense. It is a political science paper in that Newman et al. (2009) do two things there:
1. Wave a big stick regarding the model. They say "Our model can deep dive into nonlinear territory and provide consistent results." This is important.
2. The Montreal Protocol is a powerful and successful policy apparatus to control industrial emissions that affect the atmosphere.
One might read into this something like "the Montreal Protocol is successful and the Tokyo Protocol is not."