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A warm Miocene climate at low atmospheric CO 2 levels
Author(s) -
Knorr G.,
Butzin M.,
Micheels A.,
Lohmann G.
Publication year - 2011
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 - 10.1029/2011gl048873
Subject(s) - climatology , forcing (mathematics) , environmental science , albedo (alchemy) , climate change , atmospheric sciences , climate model , atmosphere (unit) , paleoclimatology , sea surface temperature , late miocene , water vapor , carbon dioxide in earth's atmosphere , geology , oceanography , geography , paleontology , art , structural basin , performance art , meteorology , art history
Proxy records from the Miocene epoch (∼23‐5 Ma) indicate a warmer climate than today in spite of lower atmospheric carbon dioxide (CO 2 ) concentrations in the range of preindustrial levels. As yet the simulation of a warm Miocene climate with these low CO 2 values has proven to be a challenge. In this study we present climate simulations of the Late Miocene (11‐7 Ma) with a preindustrial CO 2 level, using a coupled atmosphere‐ocean general circulation model (AOGCM). The simulated global mean surface temperature of ∼17.8 °C represents a significantly warmer climate than today. We have analyzed the relative importance of tectonic and vegetation changes as forcing factors. We find that the strongest temperature increase is due to the Late Miocene vegetation distribution, which is more than three times stronger than the impact induced by tectonic alterations. Furthermore, a combination of both forcing factors results in a global temperature increase which is lower than the sum of the individual forcing effects. Energy balance estimates suggest that a reduction in the planetary albedo and a positive water vapor feedback in a warmer atmosphere are the dominating mechanisms to explain the temperature increase. Each of these factors contributes about one half to the global temperature rise of ∼3 K. Our results suggest that a much warmer climate during the Late Miocene can be reconciled with CO 2 concentrations similar to preindustrial values.