Abstract
Abstract. Understanding the sequence of events occuring during the last major glacial to interglacial transition (21 ka BP to 9 ka BP) is a challenging task that has the potential to unveil the mechanisms behind large scale climate changes. Though many studies have focused on the understanding of the complex sequence of rapid climatic change that accompanied or interrupted the deglaciation, few have analysed it in a more theoretical framework with simple forcings. In the following, we address when and where the first significant temperature anomalies appeared when using slow varying forcing of the last deglaciation. We used here coupled transient simulations of the last deglaciation, including ocean, atmosphere and vegetation components to analyse the spatial timing of the deglaciation. To keep the analysis in a simple framework, we did not include freshwater forcings that potentially cause rapid climate shifts during that time period. We aimed to disentangle the direct and subsequent response of the climate system to slow forcing and moreover, the location where those changes are more clearly expressed. In a data – modelling comparison perspective, this could help understand the physically plausible phasing between known forcings and recorded climatic changes. Our analysis of climate variability could also help to distinguish deglacial warming signals from internal climate variability. We thus are able to better pinpoint the onset of local deglaciation, as defined by the first significant local warming and further show that there is a large regional variability associated with it, even with the set of slow forcings used here. In our model, the first significant hemispheric warming occurred simultaneously in the North and in the South and is a direct response to the obliquity forcing.
Highlights
The last deglaciation – 21 to 9 kyrs Before Present (BP) – is Earth’s most recent transition from a glacial-like climate to an interglacial-like climate, a type of transition that occured repeatedly with a periodicity of 100 kyrs over the late Quaternary (Hays et al, 1976; Waelbroeck et al, 2002)
The orbitally-forced changes in insolation received by the Earth are the only long-term forcing truly external to the Earth’s climatic system, whereas ice-sheet waxing and waning and greenhouse gases that strongly affect the climate over similar time periods are only internal feedbacks to that one forcing
In the version applied here, components for atmosphere (ECBilt), an ocean (CLIO) and vegetation (VECODE) are activated. It is a follow-up of the ECBilt-CLIO-VECODE coupled model that has been successful in simulating a wide range of different climates from the Last Glacial Maximum (Roche et al, 2007) to the future (Driesschaert et al, 2007) through the Holocene (Renssen et al, 2005, 2009) and the last millenium (Goosse et al, 2005)
Summary
The last deglaciation – 21 to 9 kyrs Before Present (BP) – is Earth’s most recent transition from a glacial-like climate to an interglacial-like climate, a type of transition that occured repeatedly with a periodicity of 100 kyrs over the late Quaternary (Hays et al, 1976; Waelbroeck et al, 2002). Milutin Milankovitch was one of the first to propose that this low-frequency variability of the climate system is linked to the variations of the orbit of the Earth around the Sun, thereby modifying the energy received at the top of the atmosphere in summer. He proposed that summer insolation at high northern latitudes could be considered as the main driver of the ice-age cycles as it constrained the capacity of winter snow to survive the summer and contributed to the buildup of glacial ice-sheets. The response of the Earth’s system is non-linear and the exact timing of the deglaciation may be set by a threshold crossing, as is suggested by several authors (Paillard, 1998; Barker et al, 2009; Lamy et al, 2007; Wolff et al, 2009)
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