How Should Snowball Earth Deglaciation Start

Abstract

Once Earth enters a snowball Earth state (e.g., Hoffman et al., 1998, 2017), it is very difficult to recover because the whole globe will be covered by highly reflective snow and ice. Early estimates using energy balance models (EBMs) showed that 0.16-0.29 bar of CO 2 was required to deglaciate the Neoproterozoic (1,000-541 Ma) snowball Earth (Caldeira & Kasting, 1992; Tajika, 2003). Later studies using general circulation models (GCMs) obtained similar results, i.e., greater than 0.1 bar of CO 2 was required to initiate the deglaciation (Hu et al., 2011; Le Hir et al., 2007; R. T. Pierrehumbert, 2004). Extremely high CO 2 level (far greater than 0.2 bar) was required to deglaciate a snowball Earth in the GCM FOAM (Pierrehumbert, 2004, 2005), but it was later identified to be due to a caveat in its cloud parameterization (D. S. J. J. o. C. Abbot, 2014; D. S. Abbot et al., 2012). Nevertheless, the required CO 2 level to deglaciate a snowball Earth was high. To facilitate the deglaciation, deposition of volcanic dust and other terrestrial dust have been invoked to lower the surface albedo (e.g., D. Li & Pierrehumbert, 2011) or planetary albedo (D. S. Abbot & Halevy, 2010). For the latter, the surface is warmed by the atmosphere, which absorbs large amount of solar insolation due to its high dust loading (Liu et al., 2020). Voluminous dust in the atmosphere or in the ice could lower the threshold CO 2 level for snowball Earth deglaciation to a range of 0.01-0.1 bar (

A breviary of Earth’s climate changes using Stephan-Boltzmann law

“…However, several other processes may be occurring, such as the presence of melt ponds (Wu et al, 2021) and regions of net sublimation (Warren et al, 2002), particularly around the tropics, which suggested albedo may not have been greater than 0.4 -which still translates into a global temperature 16°C lower than today's-(Fig1. Ice-Snow).…”

Fine Cloud Structures on a Hard Snowball Earth

“…The threshold of CO 2 concentration to trigger the deglaciation has been extensively investigated using different energy balance models and global general circulation models (GCMs) (e.g., Abbot et al., 2012, 2013; Caldeira & Kasting, 1992; Hu et al., 2011; Hyde et al., 2000; Pierrehumbert, 2004; Pierrehumbert et al., 2011; Tajika, 2003). However, the obtained CO 2 thresholds vary from 0.01 to 0.4 bar because of divergent treatments of several processes, for example, ice/snow albedo (Pierrehumbert et al., 2011), cloud parameterization (Abbot, 2014; Abbot et al., 2012), surface dust or aerosols (Abbot & Halevy, 2010; Abbot & Pierrehumbert, 2010; de Vrese et al., 2021), atmospheric pressure (Edkins & Davies, 2021), melt ponds (Wu et al., 2020), and vertical resolution of sea ice model (Abbot et al., 2010).…”