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Late Holocene climate: Natural or anthropogenic?
Author(s) -
Ruddiman W. F.,
Fuller D. Q.,
Kutzbach J. E.,
Tzedakis P. C.,
Kaplan J. O.,
Ellis E. C.,
Vavrus S. J.,
Roberts C. N.,
Fyfe R.,
He F.,
Lemmen C.,
Woodbridge J.
Publication year - 2016
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1002/2015rg000503
Subject(s) - holocene , natural (archaeology) , ice core , physical geography , climate change , greenhouse gas , glacial period , geology , climatology , earth science , environmental science , geography , oceanography , paleontology
For more than a decade, scientists have argued about the warmth of the current interglaciation. Was the warmth of the preindustrial late Holocene natural in origin, the result of orbital changes that had not yet driven the system into a new glacial state? Or was it in considerable degree the result of humans intervening in the climate system through greenhouse gas emissions from early agriculture? Here we summarize new evidence that moves this debate forward by testing both hypotheses. By comparing late Holocene responses to those that occurred during previous interglaciations (in section 2), we assess whether the late Holocene responses look different (and thus anthropogenic) or similar (and thus natural). This comparison reveals anomalous (anthropogenic) signals. In section 3, we review paleoecological and archaeological syntheses that provide ground truth evidence on early anthropogenic releases of greenhouse gases. The available data document large early anthropogenic emissions consistent with the anthropogenic ice core anomalies, but more information is needed to constrain their size. A final section compares natural and anthropogenic interpretations of the δ 13 C trend in ice core CO 2 .