Model Sensitivity to Insolation Forcing and Uncertainties in Holocene Temperature Simulations

Abstract The persistent discrepancy between climate models and proxy records regarding temperature variations throughout the Holocene remains evident in our latest isotope‐enabled transient simulations (iTRACE). This study quantifies model sensitivity to insolation forcing and investigates the origins of the uncertainties in mid‐Holocene temperatures by combining iTRACE with multi‐model simulations from the Palaeoclimate Model Intercomparison Project (PMIP4) component of the latest phase of the Coupled Model Intercomparison Project (CMIP6). We show that inter‐model uncertainties in temperature response exceed the ensemble mean signals, particularly over the Northern Hemisphere and during boreal winter. The weak temperature response observed in most models, compared to paleoclimate reconstructions, is attributed to low sensitivity to insolation forcing, arising from insufficient local‐to‐regional feedbacks over northern mid‐to‐high latitudes. Additionally, model uncertainties in boreal summer temperatures originate from uncertainties in sea ice‐albedo feedback and shortwave‐cloud feedback. In boreal winter, model temperature uncertainties are attributed to uncertainties in air moisture content, cloud cover, and ocean heat release to the subpolar atmosphere. The mid‐Holocene temperature response is modulated by the interplay of multiple internal feedbacks within the climate system, in addition to a direct response to insolation forcing. Finally, we argue that improving the mid‐Holocene temperature simulations in mid‐high latitudes will also enhance tropical temperature simulations, as these regions are linked through meridional atmospheric heat transport.