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Reconstructions of past climate behavior often describe prominent anomalousperiods that are not necessarily captured in climate simulations. Here, weillustrate the contrast between an interdecadal strong positive phase of thewinter Pacific/North American pattern (PNA) in the early 19th centurythat is described by a PNA reconstruction based on tree rings fromnorthwestern North America, and a slight tendency towards negative winterPNA anomalies during the same period in an ensemble of state-of-the-artcoupled climate simulations. Additionally, a pseudo-proxy investigation withthe same simulation ensemble allows for assessing the robustness of PNAreconstructions using solely geophysical predictors from northwestern NorthAmerica for the last millennium. The reconstructed early 19th-centurypositive PNA anomaly emerges as a potentially reliable feature, although thepseudo-reconstructions are subject to a number of sources of uncertainty anddeficiencies highlighted especially at multidecadal and centennialtimescales. The pseudo-reconstructions demonstrate that theearly 19th-century discrepancy between reconstructed and simulated PNAdoes not stem from the reconstruction process. Instead, reconstructed andsimulated features of the early 19th-century PNA can be reconciled byinterpreting the reconstructed evolution during this time as an expressionof internal climate variability, which is unlikely to be reproduced in itsexact temporal occurrence by a small ensemble of climate simulations.However, firm attribution of the reconstructed PNA anomaly is hampered byknown limitations and deficiencies of coupled climate models anduncertainties in the early 19th-century external forcing and backgroundclimate state

Reconciling reconstructed and simulated features of the winter Pacific/North American pattern in the early 19th century