Proof-of-concept: Using ChatGPT to Translate and Modernize an Earth System Model from Fortran to Python/JAX

TL;DR

This paper demonstrates a semi-automated approach using GPT-4 to translate Earth system models from Fortran to Python/JAX, significantly improving speed, accessibility, and enabling differentiability for climate modeling.

Contribution

Introducing a GPT-4 based method for translating legacy Fortran climate models to Python/JAX, enhancing performance and differentiability for scientific research.

Findings

Python/JAX version runs up to 100x faster on GPU

Enables parameter estimation via automatic differentiation

Produces readable and classroom-friendly code

Abstract

Earth system models (ESMs) are vital for understanding past, present, and future climate, but they suffer from legacy technical infrastructure. ESMs are primarily implemented in Fortran, a language that poses a high barrier of entry for early career scientists and lacks a GPU runtime, which has become essential for continued advancement as GPU power increases and CPU scaling slows. Fortran also lacks differentiability - the capacity to differentiate through numerical code - which enables hybrid models that integrate machine learning methods. Converting an ESM from Fortran to Python/JAX could resolve these issues. This work presents a semi-automated method for translating individual model components from Fortran to Python/JAX using a large language model (GPT-4). By translating the photosynthesis model from the Community Earth System Model (CESM), we demonstrate that the Python/JAX version results in up to 100x faster runtimes using GPU parallelization, and enables parameter estimation via automatic differentiation. The Python code is also easy to read and run and could be used by instructors in the classroom. This work illustrates a path towards the ultimate goal of making climate models fast, inclusive, and differentiable.