NOAA/WDS Paleoclimatology - Northern Scandinavia, 138 BC-2006 AD, maximum latewood density, living and subfossil pine, PAGES Euro-Med 2k Version

Solar insolation changes, resulting from long-term oscillations of orbital configurations, are an important driver of Holocene climate. The forcing is substantial over the past 2,000
years, up to four times as large as the 1.6Wm-2 net anthropogenic forcing since 1750, but the trend varies considerably over time, space and with season. Using numerous high-latitude proxy records, slow orbital
changes have recently been shown6 to gradually force boreal summer temperature cooling over the common era. Here, we present new evidence based on maximum latewood
density data from northern Scandinavia, indicating that this cooling trend was stronger (-0.31 deg C per 1,000 years, \pm 0.03 deg C) than previously reported, and demonstrate that
this signature is missing in published tree-ring proxy records. The long-term trend now revealed in maximum latewood density data is in line with coupled general circulation
models indicating albedo-driven feedback mechanisms and substantial summer cooling over the past two millennia in northern boreal and Arctic latitudes. These findings,
together with the missing orbital signature in published dendrochronological records, suggest that large-scale nearsurface air-temperature reconstructions9–13 relying on treering
data may underestimate pre-instrumental temperatures includingwarmth during Medieval and Roman times.