Significantly warmer Arctic surface temperatures during the Pliocene indicated by multiple independent proxies

Temperatures in the Arctic have increased by an astounding 1 degrees C in response to anthropogenic forcing over the past 20 years and are expected to rise further in the coming decades. The Pliocene (2.6-5.3 Ma) is of particular interest as an analog for future warming because global temperatures were significantly warmer than today for a sustained period of time, with continental configurations similar to present. Here, we estimate mean annual temperature (MAT) based upon three independent proxies from an early Pliocene peat deposit in the Canadian High Arctic. Our proxies, including oxygen isotopes and annual ring widths (MAT = -0.5 +/- 1.9 degrees C), coexistence of paleovegetation (MAT = -0.4 +/- 4.1 degrees C), and bacterial tetraether composition in paleosols (MAT = -0.6 +/- 5.0 degrees C), yield estimates that are statistically indistinguishable. The consensus among these proxies suggests that Arctic temperatures were similar to 19 degrees C warmer during the Pliocene than at present, while atmospheric CO2 concentrations were similar to 390 ppmv. These elevated Arctic Pliocene temperatures result in a greatly reduced and asymmetrical latitudinal temperature gradient that is probably the result of increased poleward heat transport and decreased albedo. These results indicate that Arctic temperatures may be exceedingly sensitive to anthropogenic CO2 emissions.