Publication Abstracts

Chandler and Sohl 2000

Chandler, M.A., and L.E. Sohl, 2000: Climate forcings and the initiation of low-latitude ice sheets during the Neoproterozoic Varanger glacial interval. J. Geophys. Res., 105, 20737-20756, doi:10.1029/2000JD900221.

The GISS GCM was used to determine if a diverse set of climate forcings, alone or in combination, could have initiated the low-latitude ice sheets of the Varanger (∼600 Ma) glacial interval. The simulations use a realistic reconstruction of the paleocontinental distribution and test the following forcings, alone and in combination: 6 percent solar luminosity decrease, four atmospheric CO2 scenarios (1260 ppm, 315 ppm, 140 ppm and 40 ppm), a 50% increase and 50% decrease in ocean heat transports, and a change in obliquity to 60°. None of the forcings, individually, produced year-round snow accumulation on low-latitude continents, although the solar insolation decrease and 40 ppm CO2 scenarios allowed snow and ice to accumulate at high and mid-latitudes. Combining forcings further cools the climate: when solar luminosity, CO2 and ocean heat transports were all decreased, annual mean freezing and snow accumulation extended across tropical continents. No simulation would have initiated low-latitude glaciation without contemporaneous glaciation at higher latitudes, a finding that matches the distribution of glacial deposits, but which argues against high obliquity as a cause of the Varanger ice age. Low-level clouds increased in most scenarios, as did surface albedo, while atmospheric water vapor amounts declined; all are positive feedbacks that drive temperatures lower. In the most severe scenario, global snow and ice cover increased to 68%, compared to 12% under modern conditions, and water vapor dropped by 90%. These results do not necessarily preclude a "snowball" Earth climate scenario for the Varanger glacial interval. However, either more severe forcings existed, or radical changes occurred in the ocean/atmosphere system that are unaccounted for by the GCM. Also, as sea ice extent increased in these experiments, snow accumulation began to decline, owing to an increasingly dry atmosphere. Under snowball Earth conditions glaciation would be impossible, since the hydrological cycle would all but cease if the atmosphere's primary moisture source were cut off.

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BibTeX Citation

@article{ch08000d,
  author={Chandler, M. A. and Sohl, L. E.},
  title={Climate forcings and the initiation of low-latitude ice sheets during the Neoproterozoic Varanger glacial interval},
  year={2000},
  journal={Journal of Geophysical Research},
  volume={105},
  pages={20737--20756},
  doi={10.1029/2000JD900221},
}

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RIS Citation

TY  - JOUR
ID  - ch08000d
AU  - Chandler, M. A.
AU  - Sohl, L. E.
PY  - 2000
TI  - Climate forcings and the initiation of low-latitude ice sheets during the Neoproterozoic Varanger glacial interval
JA  - J. Geophys. Res.
JO  - Journal of Geophysical Research
VL  - 105
SP  - 20737
EP  - 20756
DO  - 10.1029/2000JD900221
ER  -

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