The MIS 11 – MIS 1 analogy, southern European vegetation, atmospheric methane and the "early anthropogenic hypothesis"

Abstract

Abstract. Marine Isotope Stage (MIS) 11 has been considered a potential analogue for the Holocene and its future evolution. However, a dichotomy has emerged over the precise chronological alignment of the two intervals, with one solution favouring a synchronization of the precession signal and another of the obliquity signal. The two schemes lead to different implications over the natural length of the current interglacial and the underlying causes of the evolution of greenhouse gas concentrations. Here, the close coupling observed between changes in southern European tree populations and atmospheric methane concentrations in previous interglacials is used to evaluate the natural vs. anthropogenic contribution to Holocene methane emissions and assess the two alignment schemes. Comparison of the vegetation trends in MIS 1 and MIS 11 favours a precessional alignment, which would suggest that the Holocene is nearing the end of its natural course. This, combined with the divergence between methane concentrations and temperate tree populations after 5 kyr BP, provides some support for the notion that the Holocene methane trend may be anomalous compared to previous interglacials. In contrast, comparison of MIS 1 with MIS 19, which may represent a closer astronomical analogue than MIS 11, leads to substantially different conclusions on the projected natural duration of the current interglacial and the extent of the anthropogenic contribution to the Holocene methane budget. As answers vary with the choice of analogue, resolution of these issues using past interglacials remains elusive.

Global and regional sea surface temperature trends during Marine Isotope Stage 11

“…The presence of an extended "climatic optimum", lasting around 30 kyr, has been documented in sea surface temperature records across the world ocean (McManus et al, 1999;Hodell et al, 2000;Kandiano and Bauch, 2003;De Abreu et al, 2005;Dickson et al, 2009;Stein et al, 2009;Voelker et al, 2010), in temperature proxies from Antarctic ice cores (Petit et al, 1999;Pol et al, 2011) and in terrestrial pollen records (Tzedakis, 2010). Like the Holocene, the MIS11 climatic optimum appears to have been a stable interglacial period McManus et al, 1999), characterized by low-amplitude millennial-scale climate variability Healey and Thunell, 2004;Pol et al, 2011;Vázquez Riveiros et al, 2013).…”

“…Higher variance in the proxy data may result from noise and calibration uncertainties, or from uncertainties in seasonal and/or vertical attribution in the proxy records, as also suggested by Brewer et al (2007) and Sundqvist et al (2010) as well as from a different temporal SST resolution. The latter phenomenon, however, should , 982 [g] , 983 [h,i,j,k] (Laskar et al, 2004)), (B) relative temperature changes in the South Atlantic and Southern Ocean and Antarctic temperature changes recorded in the Dome C ice core during MIS11 [a]) (thin pink line: original data; thick pink line: smoothed curve), (C) mean relative temperature change in the North Atlantic records with high loadings to the first EOF and CO 2 concentration recorded in the Dome C ice core from the Antarctic (Siegenthaler et al, 2005;[b]), and (D) relative sea-level changes in the Red Sea (Rohling et al, 2009;[c]) and the LR04 benthic stack (Lisiecki and Raymo, 2005;[l]). Scores of the second EOF mean relative temperature changes in records with high positive loadings (> 0.75) on the second EOF versus (E) δ 18 O of sea water as proxy for ice volume (Elderfield et al, 2012;[d]), and (F) mean δ 13 C values in the North Atlantic as a proxy for North Atlantic deep water (NADW) strength and the East Asian winter monsoon signal as reflected by the GT32 grain size (content of > 32 µm particles) in loess sequences (Hao et al 2012;; note inverse scale).…”

“…However, whereas the present interglaciation has so far lasted through one single summer insolation maximum at 65 • N, the MIS11 interglacial optimum spans two such insolation maxima. Further, the deglaciation culminating in MIS11 climatic optimum (Termination V) was associated with an unusually weak orbital forcing and a different phasing of precession and obliquity, making orbital alignment with the Holocene difficult, and driving a protracted deglacial sea-level rise during Termination V, twice as long as during Termination I (Lisiecki and Raymo, 2005;Rohling et al, 2010;Tzedakis, 2010). In contrast to the differences in orbital parameters, the greenhouse gas concentrations in the atmosphere during MIS11 and the rate of their increase during Termination V were similar when compared to the preindustrial Holocene (Petit et al, 1999;Siegenthaler et al, 2005).…”

Sub-decadal- to decadal-scale climate cyclicity during the Holsteinian interglacial (MIS 11) evidenced in annually laminated sediments

“…A number of proxy datasets have provided insights into the long-term comparability between MIS 11 and the present interglacial (e.g. McManus et al, 2003;de Abreu et al, 2005;Helmke et al, 2008;Rohling et al, 2010;Tzedakis, 2010), but owing to a lack of data with sufficiently high temporal resolution, the short-term comparability between the two interglacials has remained ambiguous.…”

Conceptions of time in (paleo)climate science and some implications

“…However intractable such disagreements may be given the paucity of evidence, or the lack of understanding of complex interacting processes, there is a need to agree on how best to communicate contested topics, especially those involving a temporal dimension, to nonacademic audiences. Climate scientists may disagree for instance on whether the next Ice Age is either imminent and being kept at bay by anthropogenic climate forcing,57,58 or about 10,000 years off 59. They do though need to agree on how to explain why research over such varying timescales, where the crucial point of disagreement is millennial in extent, has any relevance for climate today and the immediate future.…”