Functionality of Ice Line Latitudinal EBM Tenacity (FILLET). Protocol Version 1.1

TL;DR

FILLET provides a standardized exoplanet intercomparison protocol for Earth-like EBMs to address variability in climate predictions across models. The v1.1 update expands the parameter space—most notably extending the CO$_2$ abundance range to $[1,10^5]$ ppm—and updates outputs to include two ice-edge latitudes per hemisphere, the diffusion coefficient, and $OLR$, enabling robust discrimination of snowball to ice-free states. Key contributions include revised Benchmarks/Experiments, a 50-point logarithmic CO$_2$ grid for Experiment 4, and comprehensive ice-edge and radiative outputs that support ensemble statistics. The work aims to deliver a CMIP-like ensemble (mean and standard deviation) for Earth-like exoplanet climates, enhancing robustness for observational planning and the search for life beyond the Solar System.

Abstract

The Functionality of Ice Line Latitudinal EBM Tenacity (FILLET) project is a CUISINES exoplanet model intercomparison project (exo-MIP) that compares various energy balance models (EBMs) through a series of numerical experiments. The objective is to establish rigorous protocols that enable the identification of intrinsic differences among EBMs that could lead to model-dependent results for past, current, and future EBM studies. Such efforts also provide the community with an EBM ensemble average and standard deviation, rather than a single model prediction, on benchmark cases typically used by EBM studies. These experiments include Earth-like planets at different obliquity, instellation, and carbon dioxide abundance. Here we update the v1.0 protocol (Deitrick et al., 2023) to accommodate the requirements of previously untested community models. In particular, we expand the range of carbon dioxide abundances for Experiment 4 to ensure any code will capture both snowball and ice-free end states. Additionally, participants are now required to report two ice edge latitudes per hemisphere to fully distinguish all climate states (snowball, ice caps, ice belts, and ice-free). The outputs described in FILLET protocol version 1.0 have also now been revised to include the maximum and minimum ice extent, in latitude, for each hemisphere, as well as the diffusion coefficient and outgoing longwave radiative flux.