The Miocene (24 to 5 million years ago) was<br/>a period of relative global warmth compared to the Quaternary<br/>(2 million years ago to present; e.g. Zachos et al.,<br/>2001) and was characterised by the intermittent glaciation<br/>of Antarctica only. Paradoxically, the majority of available<br/>proxy data suggest that during the Miocene, pCO2 was similar,<br/>or even lower, than the pre-industrial levels (280 ppmv;<br/>Pagani et al., 1999; Pearson and Palmer, 2000; K¨urschner<br/>et al., 1996, 2008) and at times probably crossed the modelled<br/>threshold value required for sustained glaciation in the<br/>Northern Hemisphere (DeConto et al., 2008). Records of<br/>ice rafted debris and the oxygen isotope composition of benthic<br/>foraminifera suggest that at several times over the last<br/>25 million years substantial amounts of continental ice did<br/>build up in the Northern Hemisphere but none of these led<br/>to prolonged glaciation. In this contribution, we review evidence<br/>that suggests that in the Miocene the North American<br/>Cordillera was, at least in parts, considerably lower than today.<br/>We present new GCM simulations that imply that small<br/>amounts of uplift of the North American Cordillera result<br/>in significant cooling of the northern North American Continent.<br/>Offline ice sheet modelling, driven by these GCM<br/>outputs, suggests that with a reduced topography, inception<br/>of the Cordilleran ice sheet is prohibited. This suggests that<br/>uplift of the North American Cordillera in the Late Miocene<br/>may have played an important role in priming the climate for<br/>the intensification of Northern Hemisphere glaciation in the<br/>Late Pliocene
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