Influence of Orbital Forcing on the Snowball Earth Deglaciation.

Neoproterozoic snowball Earth events lasted for multiple million years, experiencing many orbital cycles. Here we investigate whether the deglaciation of these events would be triggered more easily at certain orbital configurations than others, by using an atmosphere‐land model that considers meltpond formation on land ice. Results show that the threshold concentration of atmospheric CO2 (pCO2) required for deglaciation can vary from 6 to 10 × 104 ppmv under different orbital forcings. The threshold pCO2 decreases with the equatorial maximum monthly insolation (EMMI), which is affected most by the eccentricity and secondarily by obliquity. Therefore, we conclude that the snowball Earth deglaciation likely occurred when the eccentricity was high and obliquity was low. Compared to previous estimate that used present‐day orbital configuration which has a minimal eccentricity, the duration of snowball Earth events would likely be much shorter when the influence of orbital variations are considered. Plain Language Summary: This study explores how different orbital configurations might have influenced the termination of the Neoproterozoic snowball Earth events, during which Earth was covered by ice globally. Using a coupled atmosphere‐land model that is capable of simulating the formation of melt ponds on ice, we find that the atmospheric CO2 level needed to initiate the deglaciation varies with the Earth's orbital configurations. Specifically, the required CO2 levels are lower when the maximum monthly solar insolation received at the equator is higher, which is achieved when the Earth's orbit is more eccentric and the tilt of Earth's rotational axis is small. The results suggest that the duration of snowball Earth events could have been shorter when the influence of orbital forcing is considered. Key Points: Influence of orbital forcing on the snowball Earth deglaciation is tested using an atmosphere‐land model that considers meltpond on iceThe equatorial maximum monthly insolation is the most important factor that triggers the deglaciation of a snowball EarthThe needed CO2 to deglaciate a snowball Earth at the optimal orbital configuration is 40% lower than that under modern orbit [ABSTRACT FROM AUTHOR]