I had hoped for Julia.

If the margins are so tight that 1 day can only produce 2.5 days of simulation, why to lose even a small margin with Julia?

How do you know they would lose a significant margin with Julia?

There were talks about it in the Climate modelling arena, and around a 10% slower was mentioned in some discussions.

Well, if that's not hard data!

Please can you specify what do you mean?

I believe the parent was trying to say that the information provided is anecdotal, and that they would prefer hard data. They were doing this in an exasperated tone--the full version of their expression would be some version of "If that isn't hard data, I don't know what is!", and is meant ironically in this context.

For reference: https://clima.caltech.edu/

Most of what they do in the Climate simulation arena uses fortran, this case not being an exception, reason being other language would be less efficient --- and thus more climate endangering emissions would be produced. Plotting and data wrangling is another story.

They don't use FORTRAN because of efficiency or emissions reductions lol, they use FORTRAN because they always did and the sort of scientists who do modelling rarely see any reason to upgrade their skills or tools.

Programming is something scientists tend to study only as far as needed to get results that look right. This is how the most influential COVID model ended up being a 15,000 line student-quality C program with hundreds of single-letter name global variables.

Fortran is no longer in ALL CAPS.

When will people learn it..

They definitely stick to it, and it might be that they build convenient narratives about it. Mind you that the energy use of climate simulations is not trivial, or do you think such machine can be fed with a typical electric installation from a regular office?