Can we reliably reconstruct the mid-Pliocene Warm Period with sparse data and uncertain models?

Abstract. We present a reconstruction of the surface climate of the mid-Pliocene Warm Period (mPWP), specifically Marine Isotope Stage (MIS) KM5c or 3.205 Ma. We combine the ensemble of climate model simulations which contributed to the PlioMIP projects, with compilations of proxy data analyses of sea surface temperature (SST). The different data sets we considered are all sparse with high uncertainty, and the best estimate annual global mean surface air temperature (SAT) anomaly varies from 1.0 up to 4.7 °C depending on data source.

We argue that the latest PlioVAR analysis of alkenone data is likely more reliable than other data sets we consider, and using this data set yields a SAT anomaly of 3.6 ± 1.0 °C, with a value of 2.8 ± 0.9 °C for SST (all uncertainties are quoted at one standard deviation). However, depending on the application, it may be advisable to consider the wider range to account for structural uncertainty. The regional scale information in the reconstruction may not be reliable as it is largely based on the patterns simulated by the models. Nevertheless, despite the uncertainties, there is some indication that polar amplification may be underestimated in the models.