About the difficulty to find a Pleistocene analogue to the Holocene and Anthropocene
(2013) The 4th PAGES Open Science Meeting — Location: Goa, india (13.February.2013)
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- Abstract
- To understand better our current interglacial and its future, we have investigated the response of the climate system to insolation and GHG at the peaks of the interglacials over the past 800,000 years using both LOVECLIM (Yin and Berger, 2010, 2012) and CCSM3 (Herold et al., in press). If we identify these peaks with NH summer at perihelion, MIS-1, MIS-11 and MIS-19 show a pretty similar latitudinal and seasonal distribution of the incoming solar radiation. When compared to the average of the last 9 interglacials, they are under-insolated over the whole globe during boreal summer and are overinsolated during boreal winter with a maximum at the South Pole. This insolation distribution leads to a cooling over all the continents in boreal summer and to a warming over the whole Earth, except the Arctic, in boreal winter. A warming over the Southern Ocean in austral winter occurs during MIS-1 and MIS-19 due to the summer remnant effect of insolation. However, this does not happen in MIS11 because the large global cooling during this season is dominating the remnant effect of the austral summer. This leads to MIS-11 being a cool insolation-induced interglacials and thus not as good an analogue of MIS-1 as MIS-19, at least as far as insolation is concerned. The CO2e of MIS-1 and MIS-19 is also practically the same (265 ppmv) but is larger for MIS-11 (286 ppmv). This pretty low value for MIS-1 and MIS-19 cools the Earth, reinforcing the insolation-induced cooling during boreal summer and moderating the warming during boreal winter. The reverse happens for MIS-11 for which its higher value allows it to be finally classified among the warm interglacials. The best analogue to MIS-1 depends therefore upon the criteria used to select such an analogue. If we look now for analogues of the whole Holocene and its future, it must be stressed that the next minimum of eccentricity at the 400-ka time scale is approaching. With this and a CO2 concentration at the interglacial level, and even larger under human influence, our interglacial was predicted to be exceptionally long (Berger and Loutre, 2002). The same happened during MIS-11, its long duration having been confirmed by the EPICA record (Jouzel et al., 2007). According to the sensitivity experiments of Berger et al. (1999), moderate values of CO2 sustained for sufficiently long might have led to an interglacial MIS-19 even much longer than MIS-11 and MIS-1. The interglacials MIS-9 and MIS-5 are the warmest over the last 800 ka and, as such, are considered as analogues for our CO2-induced future warm interglacial, although their astronomical forcings are largely different from MIS-1 and its future. MIS-9 is the warmest and MIS-5, which is generally assumed to be a good analogue for the future warmth of our interglacial, is slightly warmer than the simulated present-day climate. During boreal winter, both MIS-5 and MIS-9 are cooler than the climate of a 2xCO2 atmospheric concentration simulated under Pre-Industrial conditions all over the Earth, especially over the continents. During boreal summer, they are much warmer over the continents, but remain cooler over the oceans. This shows the importance of the insolation which is much larger at MIS-5 and MIS-9 (even at MIS-11 and MIS-19) with boreal summer occurring at perihelion than in the future with boreal summer occurring at aphelion.
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Berger, A., Yin, Q., & Herold N. (2013). About the difficulty to find a Pleistocene analogue to the Holocene and Anthropocene. The 4th PAGES Open Science Meeting, Goa, india. https://hdl.handle.net/2078.5/125394