Dorian Schuyler Abbot

abbot at uchicago dot edu
(773) 834-3048

Room 461
Hinds Geophysical Sciences Building
University of Chicago
5734 South Ellis Avenue
Chicago, IL 60637

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Research

Overview

My research focuses on general and fundamental problems in climate dynamics. I consider limiting examples of climate behavior, vastly different from modern Earth. The tools I use for this research are physical theory and numerical climate models of a hierarchy of complexity. Below are brief descriptions of work I have done on a few problems that I am still interested in.

Snowball Earth Equable Climates Extrasolar Planets and Habitability

Snowball Earth

There appear to have been times (about 635, 710, and 2200 million years ago) when there were ice ages so cold that glaciers extended all the way to down sea level at the equator. In fact, the entire ocean may have been covered in sea ice up to 1-2 kilometers thick. These periods are called Snowball Earth events, and the possibility of their existence may be the most romantic and fascinating idea in all of Earth sciences!

If a Snowball event did ever happen, there must be some way for it to end since we are not in a Snowball now. Unfortunately, it has been hard to understand how Earth could escape from a Snowball state, at least one with ice-covered oceans, using physical laws. My colleagues and I have proposed that dust aersols and dust on the surface of glaciers could absorb enough of the Sun's energy to significantly alter the Snowball energy budget. These potentially important effects have not been included in previous calculations and we find that Snowball deglaciation is much easier to explain when we perform new calculations including them.

I am also involved in a project attempting to understand the initiation of Snowball Earth events, the details of which are still debated. Some scientists have proposed that the Snowballs were actually "Slushballs" with open ocean in the tropics, rather than global sea ice coverage. The appeal of a Slushball model is that it would make it easier to understand the survival of life through the Snowball episodes. Our work on Snowball initiation is relevant for the Snowball/Slushball debate, because it should help us to understand how and whether large an area of tropical ocean can stably remain ice-free during a massive glaciation.

Finally, I proposed an alternative climate state that is nearly a full Snowball, but not completely ice-covered. This state is possible if the sea ice proceeds equatorward into the global desert zone in the subtropics so that bare sea ice, without snow on top, is exposed. Bare sea ice has a much lower reflectivity, which makes it easier for a state that is nearly completely ice-covered to exist without completely freezing over. My colleagues and I were able to demonstrate that this state is possible in different global climate models and in a simpler analytical climate model, if the appropriate modifications are made. We called this climate state a Jormungand, after the world serpent in Norse mythology, because the narrow band of open ocean snakes around the planet. The Jormungand state is an appealing potential model for the Snowball Earth events because it is so close to a fully glaciated Snowball that it shares many of the full Snowball's properties, which allows the Jormungand to explain geological data, but it also has enough open ocean for life to easily survive the event.

selected publications:

  1. Abbot, D.S. and R. T. Pierrehumbert (2010), Mudball: Surface dust and Snowball Earth deglaciation, Journal of Geophysical Research, 115, D03104, doi:10.1029/2009JD012007. [PDF]

    press: New Scientist, Membrana, Teadus, Forte, Globedia, China National News, Web India

  2. Abbot, D.S. and I. Halevy (2010), Dust Aerosol Important for Snowball Earth Deglaciation, Journal of Climate, 23(15), 4121-4132, DOI: 10.1175/2010JCLI3378.1. [PDF]

  3. Abbot, D.S., I. Eisenman, and R.T. Pierrehumbert (2010), The Importance of Ice Resolution for Snowball Climate and Deglaciation, Journal of Climate, 23(22), 6100-6109, DOI: 10.1175/2010JCLI3693.1. [PDF]

  4. Voigt, A., D.S. Abbot, R.T. Pierrehumbert, and J. Marotzke (2011), Initiation of a Marinoan Snowball Earth in a state-of-the-art atmosphere-ocean general circulation model, Clim. Past, 7, 249-263, doi:10.5194/cp-7-249-2011. [PDF]

  5. Abbot, D.S., A. Voigt, and D. Koll (2011), The Jormungand Global Climate State and Implications for Neoproterozoic Glaciations, Journal of Geophysical Research, 116, D18103, doi:10.1029/2011JD015927. [PDF]

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Equable Climates

Among the strange and mysterious climates of Earth's history are those of the late Cretaceous, Paleocene, and Eocene (about 100 million years ago to about 35 million years ago). A wide variety of data indicate that surface temperatures during this period were extremely warm at high latitudes, especially during winter and in continental interiors. Simple examples include fossilized palm trees in Wyoming and crocodiles on islands in the Arctic ocean. At the same time, equatorial temperatures were either roughly the same or only somewhat higher than modern. This type of climate is called "equable" because both (1) the temperature difference between the poles and the equator and (2) the temperature difference between summer and winter were relatively small.

When the most sophisticated climate models are run with continental configurations (where the continents are, they move over millions of years!) and carbon dioxide (CO2) values corresponding to our best guess for what they should have been during the periods of equable climate, they have difficulty simulating the climate picture the data appear to be painting: either the tropics are too warm or the poles are too cold. This allows the possibility that the sophisticated climate models are missing some important physical effect that would explain equable climates. Such a physical mechanism could potentially become active in the future under global warming, increasing the uncertainty in the current climate predictions.

Eli Tziperman and I proposed a "convective cloud feedback" to help explain the mismatch between data and models during equable climates. The basic idea is that as you increase the CO2 and warm Earth, you eventually initiate atmospheric convection at high latitudes, which leads to thick convective clouds that absorb infrared radiation leaving Earth and warm it up. We first proposed the idea using a simple model to describe Earth's climate, and have since refined the idea using a hierarchy of models of different complexity (up to the most complex models) and analytical analysis (pencil and paper).

selected publications:

  1. Abbot, D.S. and E. Tziperman (2008), A High Latitude Convective Cloud Feedback and Equable Climates, Quarterly Journal of the Royal Meteorological Society, 134(630), 165-185, DOI: 10.1002/qj.211. [PDF]

  2. Abbot, D.S. and E. Tziperman (2008), Sea Ice, High Latitude Convection, and Equable Climates, Geophysical Research Letters, 35(3), L03702, doi:10.1029/2007GL032286. [PDF] [Supplementary Material PDF]

  3. Abbot, D.S. and E. Tziperman (2009), Controls on the Activation and Strength of a High Latitude Convective Cloud Feedback, Journal of the Atmospheric Sciences, 66(2), 519-529, DOI: 10.1175/2008JAS2840.1. [PDF]

  4. Abbot, D.S., M. Huber, G. Bousquet, and C.C. Walker (2009), High-CO2 Cloud Radiative Forcing Feedback over both Land and Ocean in a Global Climate Model, Geophysical Research Letters, 36, L05702, doi:10.1029/2008GL036703. [PDF] [Supplementary Material PDF]

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Extrasolar Planets and Habitability

The rapidly expanding field of extrasolar planets is a significant new source of data and ideas relevant for climate theory. Additionally, there are many potential applications of climate theory to extrasolar planet studies. I have recently begun collaborating with astronomers on the intersection of our fields.

selected publications:

  1. Abbot, D.S. and E.R. Switzer (2011), The Steppenwolf: A proposal for a habitable planet in interstellar space, Astrophysical Journal Letters, 735:L27, doi:10.1088/2041-8205/735/2/L27. [PDF]

    press: Science, Science Blog, Wired, New Scientist, National Geographic, Popsci, Weird Sciences, Y Combinator, Feedzilla, Technology Review, Astrobites, Centauri Dreams

  2. Abbot, D.S., N.B. Cowan, and F.J. Ciesla (2011), The effect of land fraction on weathering and habitability, in prep.

  3. Cowan, N.B., A. Voigt, and D.S. Abbot (2011), Thermal phases of exoplanets: Disentangling eccentricity, obliquity, and climate, in prep.

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