Abstract
Abstract. The late Miocene palaeorecord provides evidence for a warmer and wetter climate than that of today, and there is uncertainty in the palaeo-CO2 record of at least 200 ppm. We present results from fully coupled atmosphere-ocean-vegetation simulations for the late Miocene that examine the relative roles of palaeogeography (topography and ice sheet geometry) and CO2 concentration in the determination of late Miocene climate through comprehensive terrestrial model-data comparisons. Assuming that these data accurately reflect the late Miocene climate, and that the late Miocene palaeogeographic reconstruction used in the model is robust, then results indicate that: 1. Both palaeogeography and atmospheric CO2 contribute to the proxy-derived precipitation differences between the late Miocene and modern reference climates. However these contributions exibit synergy and so do not add linearly. 2. The vast majority of the proxy-derived temperature differences between the late Miocene and modern reference climates can only be accounted for if we assume a palaeo-CO2 concentration towards the higher end of the range of estimates.
Highlights
The terrestrial palaeorecord contains evidence that the late Miocene (11.61–5.33 Ma; Gradstein et al, 2004; Hilgen et al, 2005) climate was, in many regions, much warmer and/or wetter than today (e.g. Pound et al, 2011, 2012)
Late Miocene Data - Modern Observations (CTRLc) Fauna details that the palaeogeographic changes result in a simulation that overlaps less with the mean annual temperature (MAT) data than the modern potential natural climate estimates overlap, but that overall the modelled MATs are closer to the data reconstructions (13 % better) due to improvements in the distance to overlap, mostly seen in the model–data comparison of Tortonian-aged datapoints
They clearly show that the MATs of LM400c are an improvement in their match to the data reconstructions compared to the MATs of LM280c (Table 3, 225 datapoints are closer to model–data overlap in the LM400c than the LM280c – an improvement of 52 % overall, and a 36 % improvement in the number of overlaps)
Summary
The terrestrial palaeorecord contains evidence that the late Miocene (11.61–5.33 Ma; Gradstein et al, 2004; Hilgen et al, 2005) climate was, in many regions, much warmer and/or wetter than today (e.g. Pound et al, 2011, 2012). Significant differences existed in the oceans too, e.g. there is evidence for an open Panama gateway between the Atlantic and Pacific Oceans (Keigwin, 1982; Duque-Caro, 1990) and Published by Copernicus Publications on behalf of the European Geosciences Union. Bradshaw et al.: The relative roles of CO2 and palaeogeography an unrestricted Indonesian seaway between the Pacific and Indian Oceans (van Andel et al, 1975; Edwards, 1975; Kennett et al, 1985; Cane and Molnar, 2001) during the late Miocene
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