Climate forcings and the initiation of low-latitude ice sheets during the Neoproterozoic Varanger glacial interval

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