Stratospheric modulation of the Boreal response to Pliocene tropical Pacific sea surface temperatures

Variations in the sea surface temperature of the Eastern Equatorial Pacific, usually associated with the El Niño Southern Oscillation, have a global impact. Previous work has shown that the stratosphere modulates the Northern Hemisphere response to these temperature anomalies. Here, we show that the stratosphere also plays a major role in modulating the response to tropical sea surface temperature anomalies representative of the mean state of the Pliocene era, approximately four million years ago. Key to the response is a predominance of sudden stratospheric warmings during boreal winter, which cause a large anomalous surface pressure response over the North Atlantic Ocean. The stratospheric modulation results in relatively cold winter/spring Eurasian surface temperatures and relatively warm surface temperatures in Greenland and North America. The implications of these results for simulating and understanding the climate of the Pliocene era are discussed.