North American Hydroclimate During Past Warms States: A Proxy Compilation-Model Comparison for the Last Interglacial and the Mid-Holocene

During the mid-Holocene (MH: similar to 6,000 years Before Present) and Last Interglacial LIG (LIG: similar to 129,000-116,000 years Before Present) differences in the seasonal and latitudinal distribution of insolation drove Northern Hemisphere high-latitude warming comparable to that projected for the end of the 21st century in low emissions scenarios. Paleoclimate proxy records point to distinct but regionally variable hydroclimatic changes during these past warm intervals. However, model simulations have generally disagreed on North American regional moisture patterns during the MH and LIG. To investigate how closely the latest generation of models associated with the Paleoclimate Model Intercomparison Project (PMIP4) reproduces proxy-inferred moisture patterns during recent warm periods, we compare hydroclimate output from 17 PMIP4 models with newly updated compilations of moisture-sensitive North American proxy records during the MH and LIG. Agreement is lower for the MH, with models producing wet anomalies across the western United States (US) where most proxies indicate increased aridity relative to the preindustrial period. The models that agree most closely with the LIG proxy compilation display relative wetness in the eastern US and Alaska, and dryness in the northwest and central US. An assessment of atmospheric dynamics using an ensemble of the three LIG simulations that best agree with the proxies suggests that weaker winter North Pacific pressure gradients and steeper summer North Pacific and Atlantic gradients drive LIG precipitation patterns. Our updated compilations and proxy-model comparisons offer a tool for benchmarking climate models and their performance in simulating climate states that are warmer than present. Plain Language Summary The mid-Holocene (MH) and the Last Interglacial (LIG) are the two most recent intervals that were warmer than the preindustrial and so are potentially informative analogs for future emissions scenarios. We compare the newest generation of climate models with North American precipitation patterns indicated by proxy records during the MH and LIG. We find that agreement is lower for the MH, with models producing wet anomalies across the western United States (US) where most records indicate drier conditions. Most LIG simulations show wetter conditions than the preindustrial in Alaska, northern Canada, and the southwestern US, yet the models that agree most closely with the LIG proxies also show wetness in the eastern US and aridity in the Pacific Northwest and central US. Using a subset of the three models that most closely agree with the LIG proxy records, we find that differences in LIG sea level pressure gradients in the North Pacific and North Atlantic Oceans drove shifts in the spatial and seasonal distribution of precipitation across North America. Our approach offers a strategy for assessing how well models simulate past climate during times when it was warmer than modern conditions, which may offer insight into future climate change.