Fragility of reconstructed temperature patterns over the Common Era: Implications for model evaluation

Abstract

Climate field reconstructions(CFRs) enable spatially resolved estimates of past climates, providing important insights about climate variability over the Common Era. In particular, a reconstructed "La Niña-like" pattern during the transition from the Medieval Climate Anomaly (MCA) to the Little Ice Age has been widely tied to medieval droughts in southwest North America. This pattern is now used as a key benchmark for global climate model simulations of the last millennium, which have yet to reproduce it. Here we test the pattern's robustness by using four different CFR methods and two proxy networks. With the older network, we find the reconstructed patterns to be highly method-dependent, with the La Niña-like pattern not reproduced by two of the CFR methodologies. With the updated proxy network, a globally uniform MCA emerges with all methods, in agreement with simulations from the Paleoclimate Modelling Intercomparison Project Phase 3 ensemble. Our results caution against drawing dynamical interpretations from a single CFR and affirm the importance of developing CFRs through improved statistical methodology and community-driven proxy syntheses.