The non-analogue nature of Pliocene temperature gradients

The strong warming of the North Atlantic and high latitudes in the Pliocene (5.3 – 2.6 million years ago) continually fails to be simulated in climate model simulations. Being the last period of Earth history with higher global temperatures and carbon dioxide levels similar to today, it is an important target period for palaeoclimate models. One of the key features of the Pliocene climate is the reduced meridional gradients, particularly in the high latitudes of the Northern Hemisphere. Here we show that previously unconsidered palaeogeographic changes (river routing, ocean bathymetry and additional landmass in the modern Barents Sea), in the North Atlantic region can produce significant temperature responses at high latitudes. Along with orbital forcing, this can significantly decrease equator to pole temperature gradients in the Atlantic Ocean. These additional forcings show that the large Arctic warming and significantly reduced temperature gradients in the Pliocene are not analogous to future warming and that careful consideration of all the possible climatic forcings are required to accurately simulate Pliocene climate.