Speleothem evidence for late Miocene extreme Arctic amplification – an analogue for near future anthropogenic climate change?

Abstract. The Miocene provides an excellent climatic analogue for near future anthropogenic warming, with atmospheric CO₂ concentrations and global average temperatures similar to those projected for the coming century. However, the magnitude of Miocene Arctic warming remains unclear due to the scarcity of reliable proxy data. Here we use stable oxygen isotope and trace element analyses, alongside clumped isotope and fluid inclusion palaeothermometry of speleothems to reconstruct palaeo-environmental conditions near the Siberian Arctic coast during the late Tortonian (8.68 ± 0.09 Ma). Stable oxygen isotope records suggest warmer than present temperatures. This is supported by temperature estimates based on clumped isotopes and fluid inclusions giving mean annual air temperatures between +6.6 and +11.1 °C, compared with -12.3 °C today. Trace elements records reveal a highly seasonal hydrological environment. Our estimate of >18 °C of Arctic warming supports the wider consensus of a warmer-than-present Miocene and provides a rare paleo-analogue for future Arctic amplification under high emissions scenarios. The reconstructed increase in mean surface temperature far exceeds those projected in fully coupled global climate models, even under extreme emissions scenarios. Given that climate models have consistently underestimated the extent of recent Arctic amplification, our proxy data suggest Arctic warming may exceed current projections. If Arctic warming by 2100 matches our late Miocene estimates, it would have large-scale impacts on global climate, including extensive thawing of Siberian permafrost – a vast fossil carbon store.