The Snowball Earth Hypothesis

Exploring the Myths of Runaway Climate Feedbacks

The Snowball Earth hypothesis, a theory that proposes the Earth's surface was entirely or nearly entirely frozen at least once, during the Proterozoic Eon about 650 million years ago, presents a fascinating paradox when considering the role of carbon dioxide (CO2) and the dynamics of climate feedback systems. According to this hypothesis, a series of global ice ages were so severe that they led to the glaciation of the entire planet.

An artist’s concept of the Earth frozen in snow, during one of the planet’s most severe ice ages. Source: https://www.nytimes.com/2019/12/02/science/snowball-earth-ice-age.html

Yet, the Earth eventually emerged from these frozen states into warm periods, driven by natural processes. This historical climatic event provides a compelling framework for scrutinizing the arguments surrounding current climate change narratives, particularly the emphasis on CO2 as a driver of runaway global warming.

The Snowball Earth hypothesis is supported by a variety of geological evidence. This evidence, spanning from chemical signatures in ancient rocks to the distribution of certain sediment types across different continents, paints a compelling picture of global-scale glaciation events, particularly during the Cryogenian period, roughly between 720 to 635 million years ago.

One of the most striking pieces of evidence for Snowball Earth events is the presence of glacial deposits found in regions that were at or near the equator during the Proterozoic eon. These deposits include tillites (sedimentary rocks formed by glacial action) and associated glacial striations (bedrocks scraped by glaciers). The widespread distribution of these deposits, even in tropical latitudes where glaciers are unheard of in the current climate, suggests a much colder global climate capable of supporting equatorial ice sheets.

Global Distribution of Glacial Deposits between 710 ma and 582 ma. Source: https://sites.dartmouth.edu/dujs/2010/05/30/oceans-of-ice-the-snowball-earth-theory-of-global-glaciation/

Beyond direct geological evidence, theoretical models and climate simulations support the Snowball Earth hypothesis by demonstrating that certain conditions could lead to global glaciation. These models take into account the Earth's albedo (reflectivity), atmospheric CO2 levels, and solar luminosity, showing that a decrease in CO2 or an increase in albedo could trigger a global freeze.

Together, these geological records and models provide a strong foundation for the Snowball Earth hypothesis, illustrating a time when Earth underwent extreme climate changes that profoundly impacted its surface conditions, oceans, and biosphere.

During Snowball Earth, it is hypothesized that volcanic activity continued to release CO2 into the atmosphere. With the Earth's surface covered in ice, the planet's albedo (or reflectivity) increased, reflecting more of the sun's energy back into space and perpetuating the icy conditions. However, over millions of years, the accumulation of CO2 from volcanic emissions, and the lack of plant life to absorb this CO2, gradually thickened the atmospheric blanket, trapping more heat and eventually warming the planet enough to melt the ice and end the snowball state.

This narrative suggests a natural feedback system where CO2 levels can rise significantly without leading to runaway heating. Instead, the Earth system appears capable of self-regulating, with ice ages and warm periods following each other in a cyclical pattern throughout geological history.

The recovery from Snowball Earth challenges the notion of runaway climate feedback systems, where an initial change in climate leads to effects that cause further climate change in the same direction, potentially leading to uncontrollable warming or cooling.