The identification of a Pliocene time slice(s) for data/model comparison

The characteristics of the mid-Pliocene Warm Period (3.264 to 3.025 Ma BP) have been examined using geological proxies and climate models. Whilst there is agreement between models and data, details of regional climate differ. Uncertainties in prescribed forcings and in proxy data, limit the utility of the interval to understand the dynamics of a warmer than present climate or evaluate models. This uncertainty comes, in part, from the reconstruction of a time slab rather than a time slice, where forcings required by climate models can be more adequately constrained. Here we describe the rationale and approach for identifying a time slice(s) for Pliocene environmental reconstruction. A time slice centred on 3.205 Ma BP (3.204 to 3.207 Ma BP) has been identified as a priority for investigation. It is a warm interval characterised by a negative benthic oxygen isotope excursion (0.21-0.23‰) centred on Marine Isotope Stage KM5c (KM5.3). It occurred during a period of orbital forcing which was very similar to present-day. Climate model simulations indicate that proxy temperature estimates are unlikely to be significantly affected by orbital forcing for at least a precession cycle centred on the time slice, with the North Atlantic being an important exception. As a result, uncertainties in the chronological control of proxy records will only be moderately detrimental to the synthesis of temperature data. Furthermore, proxy estimates are already able to restrict the carbon dioxide increase in the atmosphere to <120 ppmv above the pre-industrial concentration, and sea-level rise to ~22 m ± 10 m higher than present-day.