Climates of Warm Earth-like Planets I: 3-D Model Simulations

M. J. Way, A. D. Del Genio, I. Aleinov, T. L. Clune, M. Kelley, N. Y. Kiang

Published 2018-08-20Version 1

We present a large ensemble of simulations of an Earth-like world with an increasing range of insolation & length of day. We show how important cloud parameterization can be for determining the habitable zone & the importance of ocean dynamics. The ensemble uses ROCKE3D, a 3-D GCM. Insolations vary from present day Earth's value of 1360.67 up to 3959.37 Wm2. Day length is extended in increasing powers of 2 from 1 Earth sidereal day up to 256. The simulations focus on a world with modern Earth-like topography & orbital period, but with zero obliquity & eccentricity. The atmosphere is 1 bar N2 dominated with CO2=400 ppmv and CH4=1 ppmv. The simulations include two types of oceans; one without ocean heat transport (a 100 meter mixed layer ocean), while the other is a fully coupled dynamic bath-tub type ocean of maximum depth 1360 meters. As shown in other studies the dynamical regime transitions that occur as day length increases induce climate feedbacks that produce cooler temperatures, first via the reduction of water vapor despite decreasing shortwave reflection by clouds, and then via a further decrease in water vapor and increasing reflection by clouds. We show that simulations without ocean heat transport are more sensitive to insolation changes than simulations with a dynamic ocean for shorter day lengths, while simulations with longer day lengths are relatively insensitive to ocean choice. We also show that uncertainties in cloud parameterization preclude a precise determination of habitability but do not affect robust aspects of exoplanet climate sensitivity. This is the first paper in a series that will investigate aspects of habitability in the simulations presented herein. The model diagnostics datasets from this study are publicly available and we encourage their use by the community.