The early Pliocene (5 to 3 million years ago) is the period in the geological past believed to be the closest analogue to contemporary global warming. Palaeoclimate data suggest that there were persistent El Ni

The Pliocene warm interval has been difficult to explain. We reconstructed the latitudinal distribution of sea surface temperature around 4 million years ago, during the early Pliocene. Our reconstruction shows that the meridional temperature gradient between the equator and subtropics was greatly reduced, implying a vast poleward expansion of the ocean tropical warm pool.