Decrease in Hysteresis of Planetary Climate for Planets with Long Solar Days

Abstract

The ice-albedo feedback on rapidly-rotating terrestrial planets in the habitable zone can lead to abrupt transitions (bifurcations) between a warm and a snowball (ice-covered) state, bistability between these states, and hysteresis in planetary climate. This is important for planetary habitability because snowball events may trigger rises in the complexity of life, but could also endanger complex life that already exists. Recent work has shown that planets tidally locked in synchronous rotation states will transition smoothly into the snowball state rather than experiencing bifurcations. Here we investigate the structure of snowball bifurcations on planets that are tidally influenced, but not synchronously rotating, so that they experience long solar days. We use PlaSIM, an intermediatecomplexity global climate model, with a thermodynamic mixed layer ocean and the Sun's spectrum. We find that the amount of hysteresis (range in stellar flux for which there is bistability in climate) is significantly reduced for solar days with lengths of tens of Earth days, and disappears for solar days of hundreds of Earth days. These results suggest that tidally influenced planets orbiting M and K-stars that are not synchronously rotating could have much less hysteresis associated with the snowball bifurcations than they would if they were rapidly rotating. This implies that the amount of time it takes them to escape a snowball state via CO 2 outgassing would be greatly reduced, as would the period of cycling between the warm and snowball state if they have a low CO 2 outgassing rate.

Habitable Snowballs: Temperate Land Conditions, Liquid Water, and Implications for CO2 Weathering

“…These results likely do not however generalize to tidally locked planets—Checlair et al () and Abbot et al () found that tidally locked and slowly rotating planets do not undergo the same snowball hysteresis that Earth‐like planets exhibit. Our finding that bare soil subject to strong insolation can reach warm temperatures even in mostly frozen climates would apply to substellar land in such cases, but if such planets do not undergo a sharp transition from snowball conditions to globally warm conditions, then our partially temperate snowballs would simply be another state on a continuum for tidally locked planets.…”

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

“…First, we consider a climate that can contain hysteresis. The sea‐ice feedback has been known to result in hysteresis in planetary climate for a long time (Abbot et al., 2018; Budyko, 1969; Sellers, 1969; Yang et al., 2017), while several recent studies found hysteresis in warm climates due to a positive cloud feedback (Popp et al., 2016; Schneider et al., 2019). Here, we assume that the planetary albedo is specified by the following equation, possibly as a result of changes in stratiform clouds (Schneider et al., 2019): …”

The critical current of disordered superconductors near 0 K

“…Similarities with insulators -The heat-balance approach we used throughout this article is a general concept that can account for thermal bi-stabilities in various systems such as superconductors 12,22,[26][27][28][29] , insulators 20,25 , and even in earth's T 30,31 . Here its use was inspired by earlier studies of the B-driven insulating phase of a:InO 32 .…”