Navigating legacy Earth System Model software

As a Research Software Engineer in the natESM project, you have the opportunity to work with a wide range of Earth System Models (ESMs) developed by the German scientific community. Many of these models, originating in the 1990s, were predominantly written in Fortran. While the broader scientific software world has since transitioned toward languages such as C/C++ and Python, the ESM community is still in the process of catching up. As a result, legacy Fortran code—often 20 years old or more—presents unique and sometimes amusing challenges when attempting to adapt or port to modern technologies.

This talk offers a humorous look at these challenges through the eyes of an RSE navigating outdated code in order to accomplish present-day tasks. Topics will include unsustainable methods of structuring software, relic configuration files used for input, ambiguous naming conventions, unused or nonfunctional code that has never been removed, version control practices that can be improved, and other long-standing programming habits that need to evolve. The session will also highlight more modern and maintainable alternatives to these practices, offering a lighthearted yet constructive perspective on bringing legacy ESM code into the future.