Well Fortran was, notably, one of the first languages to have proper source-to-source autodiff (TAPENADE) [1-3], so it’s probably not impossible, though my choi

Well Fortran was, notably, one of the first languages to have proper source-to-source autodiff (TAPENADE) [1-3], so it’s probably not impossible, though my choice for a fully differentiable climate model would personally be Julia, like the CliMA folks at Caltech [4]. [1] https://doi.org/10.1145/2450153.2450158 https://doi.org/10.1145/2450153.2450158 [2] http://www-tapenade.inria.fr:8080/tapenade/index.jsp http://www-tapenade.inria.fr:8080/tapenade/index.jsp [3] http://www-sop.inria.fr/ecuador/tapenade/distrib/README.html http://www-sop.inria.fr/ecuador/tapenade/distrib/README.html [4] https://clima.caltech.edu/ https://clima.caltech.edu/