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Arctic climate is uniquely sensitive to ongoing warming. The feedbacks that drive this amplified response remain insufficiently quantified and misrepresented in model scenarios of future warming. Comparison with paleotemperature reconstructions from past warm intervals can help close this gap. The Early Holocene (11.7-8.2 ka BP) is an important target because Arctic temperatures were warmer than today. This study presents centennially resolved summer temperature reconstructions from three Svalbard lakes. We show that Early Holocene temperatures fluctuated between the coldest and warmest extremes of the past 12 ka, exceeding the range of instrumental observations and future projections. Peak warmth occurred similar to 10 ka BP, with temperatures 7 degrees C warmer than today due to high radiative forcing and intensified inflow of warm Atlantic waters. Between 9.5 and 8 ka BP, temperatures dropped in response to freshwater fluxes from melting ice. Facing similar mechanisms, our findings may provide insight into the near-future response of Arctic climate.

Plain Language Summary The Arctic warms much faster than the global average. This amplified response can trigger feedbacks that affect the trajectory of future change. In areas formerly covered by ice, darker open water or rocks reflect less solar heat, enhancing warming. However, freshwater from melting ice may slow ocean circulation, leading to cooling. The climate impact of these mechanisms remain insufficiently understood, restricting efforts to predict future change. To reduce uncertainty, our research uses geological information from the most recent past period when the Arctic was warmer than the present, the Early Holocene, which lasted from 11,700 to 8,200 years ago. We analyzed fats from algae preserved in Svalbard lakes that yield information about past summer temperatures. Our findings show that the Early Holocene was characterized by the coldest and warmest extremes experienced since the last Ice Age. During peak warmth, summer temperatures were 7 degrees C warmer than today as more solar radiation and warm water reached the Arctic. However, Early Holocene warming was much slower than today. But warming was interrupted when freshwater pulses from melting Ice Sheets lowered temperatures. As we face a warmer Arctic with a melting Greenland Ice Sheet, our findings provide a rare window into the region's future.