Habitable Worlds Across Time and Space STSci Symposium 2014

What Can Earth Paleoclimates Reveal About the Resiliency of Habitable States?

An Example from the Neoproterozoic Snowball Earth

Linda E. Sohl,1,2 Mark A. Chandler,1,2 Jeffrey Jonas,1,2 Alexander Pavlov,3 Thomas Clune,3 Anthony DelGenio,2 Shawn Domagal-Goldman,3 Michael Way2

1 Center for Climate Systems Research, Columbia University, New York, NY2 NASA Goddard Institute for Space Studies, New York, NY

3 NASA Goddard Space Flight Center, Greenbelt, MD

Habitable Worlds Across Time and Space STSci Symposium 2014

The Neoproterozoic “Snowball Earth”

Habitable Worlds Across Time and Space STSci Symposium 2014

How Do We Know It Was Cold?

All cold climate features found in rocks interpreted to have been deposited in

low-latitude regions

Habitable Worlds Across Time and Space STSci Symposium 2014

The “Hard Snowball Earth”

Habitable Worlds Across Time and Space STSci Symposium 2014

Conflicting Model Results

• 1D and 2D modeling produces “snapover effect” on sea ice cover once sea ice front reaches 30 degrees latitude– Tipping point is reached once sea ice front extends

under descending Hadley cell – sea ice albedo effect is self-sustaining

• 3D models with fully coupled oceans cannot achieve this frozen state unless key feedbacks are disabled (Poulsen and Jacobs, 2004)– “Slushball Earth” alternative hypothesis

Habitable Worlds Across Time and Space STSci Symposium 2014

3D Modeling of a Snowball Earth

• NASA/GISS ModelE2-R (Schmidt et al., 2014):– Atmospheric model with 2 x 2.5˚horizontal

resolution, 40 layers with top at 0.1 mb– Ocean model with 1 x 1.25˚ horizontal

resolution, 32 layers, Gent-McWilliams correction included (IPCC AR5 p5)

• Boundary conditions: – Paleogeography, no vegetation, solar

luminosity = 93.8% modern, CO2 = 40 ppm

Habitable Worlds Across Time and Space STSci Symposium 2014

Snowball Earth Global Mean Temperature: -

11.1 ˚C

Control Run Global Mean Temperature:

17.9 ˚C

Habitable Worlds Across Time and Space STSci Symposium 2014

Hypotheses

Habitable Worlds Across Time and Space STSci Symposium 2014

Snowball Earth Global Mean Temperature: -

11.1 ˚C

(Pierrehumbert, 2002)

Habitable Worlds Across Time and Space STSci Symposium 2014