Interglacials of the last 800 ka and possible Pleistocene analogues of the Holocene

Yin, Qiuzhen;Berger, Andre
(2014) Milankovitch 135 Anniversary UNESCO Symposium. Water management in transition countries as impacted by climate and other global changes, Lessons from paleoclimate, and Regional scale — Location: Belgrade (3.September.2014)

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To understand better our current interglacial and its future, we have investigated the response of the climate system to insolation and GHG during the warm intervals (Climatic Optimum) of the interglacials over the past 800,000 years using both LOVECLIM (Yin and Berger, 2010, 2012; Yin, 2013) and CCSM3 (Herold et al., 2012; Nikolova et al., 2013). A particular attention is paid to the 5 warmest interglacials MIS-1, -5, -9, -11 and -19. If we identify the peaks of the interglacials 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 over-insolated 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 the interglacial peaks are considered, their global annual mean temperatures are slightly lower than when NH summer occurs at perihelion due to a smaller obliquity and to NH fall instead of summer occurring at perihelion. MIS-5 and MIS-9 remain the warmest interglacials. MIS-11 and MIS-19 are now globally cooler than MIS-1 with a larger temperature gradient between the low and the high latitudes and no good analogue of MIS-1 can be found. All snapshot simulations of the five interglacials show a global annual mean temperature higher than pre-industrial time, except for the MIS-19 peak simulation. This similarity between the climate of MIS-19 at its δ18O peak and of the pre-industrial time extends to the regional scale and to precipitation. This leads to the possibility of using the MIS-19 climate at its δ18O peak as an analogue for the natural climate of the present-day and the next centuries, and underlines the necessity of obtaining more proxy-based climate reconstructions of high temporal resolution during MIS-19. In the transient simulations, the past interglacials are much warmer than PI in JJA, slightly warmer at the annual scale but cooler in DJF. This can be explained by the relatively small obliquity at pre-industrial time and its NH summer occurring at aphelion, both leading to much less insolation received by the Earth during boreal summer. In all simulations, 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. 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) from a simulation where a simple ice-sheet model was interactively coupled to the rest of the climate system. The same happened during MIS-11, its long duration having been confirmed by the EPICA record (Jouzel et al., 2007).
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Yin, Q., & Berger, A. (2014). Interglacials of the last 800 ka and possible Pleistocene analogues of the Holocene. Milankovitch 135 Anniversary UNESCO Symposium. Water management in transition countries as impacted by climate and other global changes, Lessons from paleoclimate, and Regional scale, Belgrade. https://hdl.handle.net/2078.5/188703