Greenland Ice Cores Reveal a South‐To‐North Difference in Holocene Thermal Maximum Timings

Holocene temperature evolution remains poorly understood. Proxies in the early and mid‐Holocene suggest a Holocene Thermal Maximum (HTM) where temperatures exceed the pre‐industrial, whereas climate models generally simulate monotonic warming. This discrepancy may reflect proxy seasonality biases or errors in climate model internal feedbacks or dynamics. Using seasonally unbiased ice core reconstructions at NEEM, NGRIP, and Greenland Ice Sheet Project 2, we identify a Greenland HTM of ∼2°C above pre‐industrial, in agreement with other Northern Hemisphere proxy reconstructions. The firn‐based reconstructions are verified through borehole thermometry, producing a multi‐core, multi‐proxy reconstruction of Greenland climate from the last glacial to pre‐industrial. HTM timing across Greenland is heterogenous, occurring earlier at high elevations. Total air content measurements suggest a temperature contribution from elevation changes; regional oceanographic conditions, a weakened polar lapse rate, or variable near‐surface inversions may also be important sensitivities. Our reconstructions support climate simulations with dynamic Holocene vegetation, highlighting the importance of vegetation feedbacks. Plain Language Summary Climate change during the Holocene, the current geological time period, is important to understand. This period began ∼11.7 thousand years ago and contains the transition from the last ice age to today. Simulations of this transition suggest that global climate continued to warm across this whole period. Proxy evidence, however, tends to suggest that warmer‐than‐modern temperatures were reached at the start of the Holocene, followed by gradual cooling. Resolving this dispute in our recent climatological past is important to verify climate model behavior, and understand nuances in proxy records. Using ice core reconstructions of Greenland climate, which broadly follows northern high‐latitude climate, we lend further support to a warm period in the early Holocene. These new records are spread across Greenland, allowing for the spatial fingerprint of this warm period to be identified. Key Points We identify a Holocene Thermal Maximum (HTM) across three Greenland ice cores of 1.6–2.6°C above pre‐industrial The HTM has a south‐to‐north difference in timing, beginning earlier at Greenland Ice Sheet Project 2 in the south (9.9 ka) and later at NEEM in the north (6.85 ka) Total air content suggests that deglacial elevation change contributes to this