Location of long-term instrumental station and tree-ring MXD records in Europe.
Abstract
The precise, annual dating control, inherent to dendrochronology, has recently been questioned througha combined analysis of tree-growth and coupled climate models (Mann et al. (2012; hereafter MAN12))suggesting single tree-rings in temperature limited environments are missing following large volcanicevents. We test this hypothesis of missing, post-volcanic rings by using a compilation of maximum late-wood density (MXD) records that are typically used for reconstructing temperature and the detectionof volcanic events, together with a unique set of long instrumental station data from Europe reachingback into the early 18th century. We investigate the temporal coherence between tree-ring MXD andobserved summer temperatures before and after the most significant, precisely dated, volcanic event ofthe past 1000 years, the 1815 Tambora eruption widely known as the cause for the 1816 “year withouta summer”. Comparison of existing and newly developed MXD chronologies from cold environments inNorthern Scandinavia (¯rNorth= 0.70, N = 3) and the European Alps, including the Pyrenees, (¯rCentral= 0.46,N = 4) reveals significant interseries correlations over the 1722–1976 common period, suggesting coher-ence among these independently developed timeseries. Comparisons of these data with observed JJAtemperatures – from 1722 to 1976, a 94-year pre-Tambora (1722–1815), and a 94-year post-Tambora(1817–1910) period – reveals significant and temporally stable correlations ranging from 0.32 to 0.68.However, if we assume the 1816 ring is missing in the MXD chronologies (i.e., shift the pre-Tambora databy one year), all proxy/instrumental correlations fall apart approaching zero. Results from an additionalexperiment, where the long instrumental record is replaced by an annually resolved, 500-year, summertemperature reconstruction derived from documentary evidence, corroborates the findings from the firstexperiment: significant positive correlations with the unmolested chronologies and zero correlation withthe perturbed chronologies back to 1500 AD. These elementary analyses indicate that either the tree-ringchronologies are correctly dated, i.e., no is ring missing in the year without a summer, or that both the longinstrumental and documentary records contain dating uncertainties. As the latter is unlikely, we concludethe MAN12 hypothesis on post-volcanic missing rings can be rejected based on simple comparisons oftree-ring, instrumental and documentary data over the past 300–500 years from Central and Northern Europe.
In: