Snowball Earth - Mechanisms

Mechanisms

The initiation of a Snowball Earth event would involve some initial cooling mechanism, which would result in an increase in the Earth's coverage of snow and ice. The increase in Earth's coverage of snow and ice would in turn increase the Earth's albedo, which would result in positive feedback for cooling. If enough snow and ice accumulates, runaway cooling would result. This positive feedback is facilitated by an equatorial continental distribution, which would allow ice to accumulate in the regions closer to the equator, where solar radiation is most direct.

Many possible triggering mechanisms could account for the beginning of a Snowball Earth, such as the eruption of a supervolcano, a reduction in the atmospheric concentration of greenhouse gases such as methane and/or carbon dioxide, changes in solar energy output, or perturbations of the Earth's orbit. Regardless of the trigger, initial cooling results in an increase in the area of the Earth's surface covered by ice and snow, and the additional ice and snow reflects more solar energy back to space, further cooling the Earth and further increasing the area of the Earth's surface covered by ice and snow. This positive feedback loop could eventually produce a frozen equator as cold as modern-day Antarctica.

Global warming associated with large accumulations of carbon dioxide in the atmosphere over millions of years, emitted primarily by volcanic activity, is the proposed trigger for melting a Snowball Earth. Due to positive feedback for melting, the eventual melting of the snow and ice covering most of the Earth's surface would require as few as 1,000 years.