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Early Earth's climate: Cloud feedback from reduced land fraction and ozone concentrations
Author(s) -
Jenkins Gregory S.
Publication year - 1995
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/95gl00818
Subject(s) - troposphere , atmospheric sciences , environmental science , climatology , cloud feedback , climate model , cloud fraction , stratosphere , cloud cover , snow , longwave , climate sensitivity , radiative transfer , climate change , meteorology , geology , cloud computing , geography , oceanography , physics , quantum mechanics , computer science , operating system
Two features of early Earth—reduced ozone (O 3 ) concentration and land fraction are investigated with a general circulation model (GCM). These features are components of a paradox (Faint‐Young Sun paradox) which has intrigued researchers for more than two decades. In this study, land fraction and O 3 concentrations are uniformly reduced by 100 percent. The reduction in O 3 takes place in the troposphere and stratosphere with all other variables held constant including present‐day land fraction. Two sensitivity tests under global ocean conditions are reported: one case with implied oceanic poleward transports of heat, the other case with no implied oceanic poleward transports of heat. The results show that the removal of land under present‐day conditions increases cloud fractions and cool surface temperatures, unless heat is transported poleward by oceans. In a third sensitivity test with zero O 3 concentrations, global mean air temperatures are increased by 2 K because of an increase in upper tropospheric and lower stratospheric clouds. The clouds enhance the greenhouse effect within the troposphere, increasing downward longwave radiation to the surface, melting sea ice and snow. Similar studies using radiative‐convective models which do not include interactive clouds do not show such surface warming.