Global climate model high-obliquity solutions to the ancient climate puzzles of the Faint-Young Sun Paradox and low-altitude Proterozoic glaciation


  • Gregory S. Jenkins


There is a general consensus that warm temperatures throughout Precambrian were caused by very high CO2 or CH4 atmospheric concentrations. Episodes of glaciation in the early and late Proterozoic were caused by a reduction in these greenhouse gases through intensive weathering or large reduction in the methane producing bacteria population. There are suggestions that these episodes were global because the continents occupied low latitudes at or near the time of glaciation. Here it is reported that high-obliquity throughout the Precambrian serves as a mechanism for producing warm temperatures throughout the Archean and glaciation in the late Proterozoic. In this paper, Global climate model simulations using high-obliquity values that range from 54° to 70° are undertaken. These simulations use a simple 50-m slab ocean, a faster rotation rate corresponding to an 18 hour day, an idealized supercontinent located in the tropics which has a north-south mountain chain and CO2 concentrations which range from 170 to 3400 ppmv. Further, four simulations under global ocean conditions, faster rotation rate and reduced solar constant (15 and 20%) using present-day and high-obliquity values have been undertaken. The simulations show warm conditions with high-obliquity but Snowball Earth conditions for the present-day obliquity in the global ocean simulations. Near Snowball Earth conditions also occur for the tropical supercontinent simulation for an obliquity of 70° and CO2 concentrations less than 1020 ppmv. Together, these simulations show that for high-obliquity the ocean remains relatively warm while land areas are cooled because of their lower heat capacity. Large fluxes of latent heat from the ocean balance the longwave energy lost at the top of the atmosphere thereby keeping high latitudes warm during winter seasons. It is suggested from this results that lower and upper limits of 65°–70° for obliquity serve as a solution for the Faint-Young Sun Paradox and low-latitude Proterozoic. Finally, the high-obliquity-climate relationship sheds some insight on the carbon isotope (δ13C) excursions during the late Proterozoic.