Evolving CO₂ Rather Than SST Leads to a Factor of Ten Decrease in GCM Convergence Time

Abstract

The response of the climate to a change inmixing ratio is a key question in the field of climate research. The equilibrium climate sensitivity (ECS) is defined as the increase in global-mean surface temperature per doubling of , 1990). Several recent studies have demonstrated a robust increase in ECS in climates warmer than modern Earth due to state-dependent feedback and forcing by 2

ExoCAM: A 3D Climate Model for Exoplanet Atmospheres

“…Still, anytime that model time steps are increased in length, whether primary, dynamical, or radiative, numerical instabilities become more common occurrences. Lastly, a recent work by Zhang et al (2021) used ExoCAM to develop an inverse modeling mode 21 in 3D. Inverse modeling, where the surface temperature is prescribed and the radiative forcings are allowed to evolve (greenhouse or solar), is commonly used in 1D models (Kopparapu et al 2013); however, Zhang et al (2021) applied the method to ExoCAM and were able to effectively duplicate the forward modeling results of Wolf et al (2018) for high-CO 2 atmospheres, while reducing the computational burden per simulation by a factor of ten.…”

“…ExoCAM has been well-received and well-used since being made public. ExoCAM, and its ancestral versions, have been employed for a wide variety of studies, including the Faint Young Sun Paradox for Earth (Wolf & Toon 2013, 2014a, high-CO 2 atmospheres (Wolf et al 2018;Zhang et al 2021), runaway and moist greenhouse thresholds for Earth (Wolf & Toon 2014b, Earth-like extrasolar planets (Wolf et al 2017;Adams et al 2019;Kang 2019aKang , 2019bKang , 2019c, habitable zone exoplanets around M-dwarf stars (Kopparapu et al 2017;Wolf 2017;Haqq-Misra et al 2018;Komacek et al , 2020aKomacek et al , 2020bWolf et al 2019;Yang et al 2019a;Hu et al 2020;Rushby et al 2020;Suissa et al 2020b;Wei et al 2020;Chen et al 2021;May et al 2021;Song & Yang 2021), planets in circumbinary systems (Wolf et al 2020), and model intercomparison studies (Yang et al 2016(Yang et al , 2019bFauchez et al 2020Turbet et al 2021). ExoCAM results have also been used off-line in projects to drive photochemistry and observability studies (Afrin Badhan et al 2019;Suissa et al 2020a).…”

Hydrologic cycle weakening in hothouse climates

“…For a given T s , the input CO 2 concentration is higher for a lower solar constant. ( C ) ExoCAM experiments with increasing CO 2 concentration for an aqua-planet with modern solar constant ( 49 ). ( D ) Small-domain fixed-SST (sea surface temperature) cloud-resolving experiments using DAM ( 22 ) and SAM ( 45 ).…”

“…We use simulation data from three atmospheric GCMs (ExoCAM, ROCKE-3D, and CAM3), two cloud-resolving models: Das Atmosphärische Modell (DAM) and System for Atmospheric Modeling (SAM), and a radiative transfer model (ExoRT) to examine the global-mean or domain-mean precipitation from cold to hot climates. ExoCAM experiments were conducted by Wolf and Toon ( 18 ), Wolf et al ( 48 ), and Zhang et al ( 49 ), ROCKE-3D experiments were performed by Way et al ( 30 ), DAM experiments were done by Seeley and Wordsworth ( 22 ), and SAM experiments were performed by Dagan et al ( 45 ). We use their output data in our analysis.…”

“…We use their output data in our analysis. Previous investigations primarily focus on surface temperature and clouds ( 18 , 30 , 48 , 49 ) or the temporal variability of precipitation ( 22 , 45 ), while our study focuses on the mean precipitation. We conduct experiments using CAM3 and ExoRT (table S1).…”