"Solar insolation changes, resulting from long-term oscillations of orbital configurations1, are an important driver of Holocene climate2, 3. The forcing is substantial over the past 2,000 years, up to four times as large as the 1.6 W m−2 net anthropogenic forcing since 1750 (ref. 4), but the trend varies considerably over time, space and with season5. 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 °C per 1,000 years, ±0.03 °C) than previously reported, and demonstrate that
- this signature is missing in published tree-ring proxy records.
State-of-the-art coupled general circulation model (CGCM) simulations and high-resolution climate reconstructions rarely extend beyond the past few hundred years, limiting possibilities to evaluate low-frequency temperature fluctuations beyond broad assessments (and debate) of the Medieval Warm Period and Little Ice Age4. In fact, most high-resolution temperature reconstructions16 including tree-ring width (TRW) records, the most widespread and important late-Holocene climate proxy17,
- have never even been compared with orbital forcing....
We here address these issues by developing a 2,000-year summer temperature reconstruction based on 587 high-precision maximum latewood density (MXD) series from northern Scandinavia (Fig. 1). The record was developed over three years using living and subfossil pine (Pinus sylvestris) trees from 14 lakes and 3 lakeshore sites >65° N (Methods), making it not only longer but also much better replicated than any existing MXD time series (for example, the widely cited Tornetraesk record contains 65 series19)."...
via Tom Nelson
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