The effects of reduced land fraction and solar forcing on the general circulation: results from the NCAR CCM

• Published in: Global and Planetary Change
• Main Author: Jenkins, Gregory S.
• Other Authors: Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI, USA
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 1993
• Subjects: Geology and Earth Sciences; Science; Sea ice
• Online Access: https://hdl.handle.net/2027.42/30769; http://www.sciencedirect.com/science/article/B6VF0-4893TWC-4/2/51ee41dcbc7803bd63b90fce3699c713; https://doi.org/10.1016/0921-8181(93)90004-8

Land fraction and the solar energy at the top of the atmosphere (solar constant) may have been significantly lower early in Earth's history. It is likely that both of these factors played some important role in the climate of the early earth. The climate changes associated with a global ocean(i.e. no continents) and reduced solar constant are examined with a general circulation model and compared with the present-day climate simulation. The general circulation model used in the study is the NCAR CCM with a swamp ocean surface. First, all land points are removed in the model and then the solar constant is reduced by 10% for this global ocean case.Results indicate that a 4 K increase in air temperature occurs with global ocean simulation compared to the control. When solar constant is reduced by 10% under global ocean conditions a 23 K decrease in air temperature is noted. The global ocean warms much of the troposphere and stratosphere, while a reduction in the solar constant cools the troposphere and stratosphere. The largest cooling occurs near the surface with the lower solar constant.Global mean values of evaporation, water vapor amounts, absorbed solar radiation and the downward longwave radiation are increased under global ocean conditions, while all are reduced when the solar constant is lowered. The global ocean simulation produces sea ice only in the highest latitudes. A frozen planet does not occur when the solar constant is reduced--rather, the ice line settles near 30[deg] of latitude. It is near this latitude that transient eddies transport large amounts of sensible heat across the ice line acting as a negative feedback under lower solar constant conditions keeping sea ice from migrating to even lower latitudes.Clouds, under lower solar forcing, also act as a negative feedback because they are reduced in higher latitudes with colder atmospheric temperatures allowing additional solar radiation to reach the surface. The overall effect of clouds in the global ocean is to act as a positive feedback ...