Did humankind prevent a Holocene glaciation?
Comment on Ruddiman's hypothesis of a pre-historic Anthropocene
by M. Claussen, V. Brovkin, R. Calov, A. Ganopolski, C Kubatzki
Recently, W.F. Ruddiman (2003, Climatic Change,Vol. 61, pp. 261-293) suggested that the anthropocene, the geolog ical epoch of significant anthropospheric interference with the natural Earth system, has started much earlier than previously thought (P. I. Crutzen and E. F. Stoermer, 2000, IGBP Newsletter,Vol. 429, pp. 623-628). Ruddiman propos ed that due to human land use, atmospheric concentrations of CO2 and CH4 began to deviate from t heir natural declining trends some 8000 and 5000 years ago, respectively. Furthermore, Ruddiman concluded that greenhous e gas concentrations grew anomalously thereby preventing natural large-scale glaciation of northern North America that sh ould have occurred some 4000-5000 years ago without human interference. Here we would like to comment on (a) natural cha nges in atmospheric CO2 concentration during the Holocene and (b) on the possibility of a Holocene glacial in ception. We substantiate our comments by modelling results which suggest that the last three interglacials are not a proper analogue for Holocene climate variations. In particular, we show that our model does not yield a glacial inception during the last several thousand years even if a declining trend in atmospheric CO2 was assumed.
