Snowball Earth: sensitivity to sea ice and surface albedo
Date
2010-02-18T19:10:22Z
Authors
Lewis, Jeffrey Philip
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The snowball Earth theory. that low-latitude continents became glaciated after sea ice extended from the poles to the equator during the Neoproterozoic (1000 - 545 Ma), has sparked a flood of numerical modelling studies investigating all phases of the proposed extreme climatic cycle. Modelling studies have both supported and refuted the original ‘hard’ snowball theory, as well as offered alternative theories such as the ‘soft’ snowball theory, where glaciers covered all land masses but sea ice did not extend equatorward of -25° latitude. Presented here are a number of sensitivity studies investigating the effects of different sea ice models on snowball inception and how large ranges in accepted albedo values affect the amount of radiative forcing required for deglaciation. These experiments shed light on disparities between previous modelling results.
This study demonstrates the importance of a sea ice component's thermodynamic formulation by comparing the physically complete thermodynamic sea ice model in the UVic Earth System Climate Model to an incomplete sea ice model used in an early version of the Fast Ocean Atmosphere Model. As well as the importance of a sound thermodynamic sea ice model is the inclusion of sea ice dynamics. Sea ice dynamics have not previously been included in snowball simulations and their inclusion suggests that the alternative `soft' snowball theory may not be plausible. With a purely thermodynamic sea ice component. the 'soft' snowball state is stable whereas with the inclusion of sea ice dynamics it is not. Also gained from this study was the influence of wind speed on the level of CO2 required to produce a hard snowball solution: greater wind speed results in a cooler ocean and easier snowball inception.
Finally, although albedo values are critical for the albedo feedback that initiates snowball inception, they are even more important for determining the amount of radiative forcing required to deglaciate the snowball Earth, as the entire planet is covered by snow and ice. Through a suit of sensitivity studies, the amount of forcing required to deglaciate a hard snowball Earth is found to be extremely sensitive to the snow albedo, sea ice albedo and snow masking depth.
Description
Keywords
paleoclimatology, proterozoic