CO2 levels required for deglaciation of a ``Near-Snowball'' Earth

Details CO2 levels required for deglaciation of a ``Near-Snowball'' Earth CO2 levels required for deglaciation of a ``Near-Snowball'' Earth

Jan 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001georl..28..283c&link_type=abstract

Geophysical Research Letters, Volume 28, Issue 2, p. 283-286

Mathematics

Logic

22

Hydrology: Glaciology, Meteorology And Atmospheric Dynamics: Paleoclimatology, Information Related To Geologic Time: Precambrian

Scientific paper

Geologic evidence suggests that in the Late Neoproterozoic (~600 Ma) almost all land masses were glaciated, with sea-level glaciation existing even at the equator. A recent modeling study has shown that it is possible to simulate an ice-covered Earth glaciation with a coupled climate/ice-sheet model. However, separate general circulation model experiments suggest that a second solution may exist with a substantial area of ice free ocean in the tropics. Although 0.1 to 0.3 of an atmosphere of CO2 (~300 to 1000 X) is required for deglaciation of a ``Snowball Earth,'' the ``exit'' CO2 levels for an open water solution could be significantly less. In this paper we utilize a coupled climate/ice sheet model to demonstrate four points: (1) the open water solution can be simulated in the coupled model if the sea ice parameter is adjusted slightly; (2) a major reduction in ice volume from the open water/equatorial ice solution occurs at a CO2 level of about 4X present values-about two orders of magnitude less than required for exit from the ``hard'' snowball initial state; (3) additional CO2 increases are required to get fuller meltback of the ice; and (4) the open water solution exhibits hysteresis properties, such that climates with the same level of CO2 may evolve into either the snowball, open water, or a warmer world solution, with the trajectory depending on initial conditions. These results set useful targets for geochemical calculations of CO2 changes associated with the open-water solution.

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