Today we are looking at the past–more specifically, the Proterozoic Eon, 2,500 to 542 million years ago. There is evidence that in this timeframe, the entire Earth was covered in glaciers, even the oceans frozen over; a global ice age referred to as ‘Snowball Earth’. How you get to a Snowball Earth state is another story; today we are focusing on how you get out of Snowball Earth.
The solution may seem obvious; temperatures warm enough to melt the ice and snow. Snowball Earth generally includes volcanoes putting more CO2 (carbon dioxide) into the atmosphere; this greenhouse gas then helps with deglaciation (the lessening of glaciers). However, data collected and simulated models put the amount of CO 2 in the atmosphere at that time as much too low to begin deglaciation. So, then, what was present millions of years ago to make our Snowball turn into the world we know today?
Today’s article is “Clouds and Snowball Earth Deglaciation“, written by Dorian S. Abbott, Aiko Voigt, Mark Branson, and Raymond T. Pierrehumbert. Published in the American Geophysical Union’s Geophysical Research Letters journal in 2012, these authors point out that clouds can act to cool a planet, or warm it.
The cooling effect of clouds is reduced by a high albedo. Albedo is a measure of reflectivity of a surface; a Snowball Earth would be highly reflective. Therefore, it would be logical that clouds above a Snowball Earth would warm the planet, instead of cooling it further. They ran six different three-dimensional models, with the same conditions for albedo, atmosphere, amount of sunlight received, and axial tilt of Earth. This was done in a way such that the main difference in temperatures between models would be created by the effect of the clouds. They found that due to the clouds warming effects, the temperature rose above freezing, and melting occurred. Even if seasonal, this suggests that Snowball Earth could have slowly melted into the present day without there being any issue with the known data for CO2 levels in the Proterozoic. Additionally, dust from volcanoes may have helped (as this would have changed the albedo of the planet). Clouds are not definitive as the answer for how Snowball Earth deglaciated, but may be part of the puzzle; the authors also call for more investigation.
Abbot, Dorian S., et al. “Clouds and Snowball Earth deglaciation.”Geophysical Research Letters. 39.20 (2012).
Today’s main article.
National Aeronautics and Space Administration. “The Blue Marble: Land Surface, Ocean Color, Sea Ice and Clouds.” Visible Earth. NASA Visible Earth. 8 Feb. 2002. Web.
The source for the image used in this post.
Stephen Marshak. Earth: Portrait of a Planet. Third Edition. New York: W. W. Norton & Company, 2007. Print.
My geology textbook, as a source for information about Snowball Earth.