Atmospheric Pressure and Snowball Earth Deglaciation

When a large amount of CO2 is added to the atmosphere, both the mixing ratio and the surface pressure increase. This causes the troposphere to expand in two directions. The greenhouse effect from the increased mixing ratio causes the tropopause pressure to decrease, so the troposphere expands upward. The increased surface pressure causes the troposphere to expand downward. The first effect is radiative and well known, while the second is nonradiative and unexplored. Here, a method is presented to compare the effect of tropospheric expansion in each direction on the surface temperature of a Snowball Earth. A series of models, from a gray model to a spectral model with realistic Snowball parameters, are used to illustrate this concept. It is shown that near the deglaciation threshold, most of the increase in surface temperature that follows an increase in CO2 is due to the nonradiative downward tropospheric expansion at the surface, not the radiative upward expansion at the tropopause. The increased atmospheric mass due to the CO2, entirely apart from its radiative effect, causes an additional increase in surface temperature and therefore aids Snowball deglaciation.

Automated summary

This study explores the impact of increased CO2 levels in the atmosphere on the expansion of the Earth's thermal layer in two directions. It is found that the expansion downward has a more significant effect on surface temperature, aiding in the deglaciation of a "Snowball Earth".