Most Earth System Models are written in Fortran, but may be re-written in another language because Fortran has some issues running on GPU based supercomputer.
Some consider using C instead, but there are many arguments to use Julia, as clima.caltech.edu are doing. https://www.nature.com/articles/d41586-019-02310-3
We started a discussion on Slack #climate, but I am posting it here to not lose the thread, and have the possibility to add more arguments.
I personally need a ~10 lines arguments to write in a whitepaper why I believe we should use Julia. (and what ESM might look like in 10 years) Here are my arguments so far:
First, obviously, Julia is fast as C and dynamic (easy to read, shorter) like Python or R.
Secondly, Julia has a large and active AI/ML libraries.
Third, Julia works great with GPU.
Fourth, Julia is more attractive for young scientists.
5th, Julia can be used directly and simply for visualization.
6th, Currently, empiricists and modelers use different languages (R/python vs. Fortran), which is a barrier to communication and collaboration. Julia would solve this.
7th, future ESMs will be modular, a Julia ESM would make it easy to add a module created by an empiricist