Estimating Summer Arctic Warming Amplitude Relative to Pre-Industrial Levels Using Tree Rings

Estimating long-term trends and short-term amplitudes requires reliable temperature (Temp) observations in the pre-industrial period when few in situ observations existed in the Arctic. Tree-ring materials are most available and used to reconstruct past Arctic Temp variations. However, most previous studies incorporated materials that are insensitive to local Temp variabilities. The derived reconstruction qualities are low (indicated by low calibration R-2), and the uncertainties inherent in the various detrending methodologies are unknown. To reconstruct Arctic (N60 degrees-N90 degrees) summer (June-August) Temp in 1850-1900 and variations over the past centuries, we screened 1116 tree-ring width and tree-ring density records and applied four detrending functions (sf-RCS, RCS, MOD, and spline). In total, 338-396 records show significant correlations (p < 0.05) with the Climate Research Unit (CRU) Temp of the corresponding grid point. These records were selected and combined into a proxy record. The achieved Arctic summer Temp reconstruction explained 45-57% of the instrumental summer Temp variance since 1950. The 2012-2021 summer Arctic warming amplitudes (1.42-1.74 degrees C) estimated by Temp anomaly datasets extending back to 1850 are within the range derived from our reconstructions, despite using various detrending methods. These findings could suggest the Berkeley and HadCRU5 datasets interpolating Temp from a few (6-73) meteorological stations could still represent the mean Arctic Temp variation in 1850-1900, and the updated reconstruction can be used as a reliable reference for 1550-2007 Arctic summer Temp history.