The influence of decision-making in tree ring-based climate reconstructions

Abstract

Tree-ring chronologies underpin the majority of annually-resolved reconstructions of Common Era climate. However, they are derived using different datasets and techniques, the ramifications of which have hitherto been little explored. Here, we report the results of a double-blind experiment that yielded 15 Northern Hemisphere summer temperature reconstructions from a common network of regional tree-ring width datasets. Taken together as an ensemble, the Common Era reconstruction mean correlates with instrumental temperatures from 1794–2016 CE at 0.79 (p < 0.001), reveals summer cooling in the years following large volcanic eruptions, and exhibits strong warming since the 1980s. Differing in their mean, variance, amplitude, sensitivity, and persistence, the ensemble members demonstrate the influence of subjectivity in the reconstruction process. We therefore recommend the routine use of ensemble reconstruction approaches to provide a more consensual picture of past climate variability.

A Song of Neither Ice nor Fire: Temperature Extremes had No Impact on Violent Conflict Among European Societies During the 2nd Millennium CE

“…They have each been shown to correlate positively with temperature variations during instrumental periods with Pearson's R values ranging from 0.7 to 0.8. One of the reconstructions in particular-the one created by Büntgen et al (2021)-averages out methodological differences and correlates very well (0.79, p < 0.001) with instrumental observations at different scales. It also has autocorrelation properties that match those of instrumental observations, and it has considerable predictive power for 20th and 21st century temperatures in the Northern Hemisphere.…”

“…Taken together, the diagnostics performed by the scientists who produced the reconstructions appear to reflect their target reasonably well. Thus, despite their imperfections, the temperature time-series very likely capture regional trends and variations during the Common Era-this is especially true for the newest ensemble reconstruction produced by Büntgen et al (2021). It is unlikely, then, that at the scale and resolution of our analysis, biases present in the temperature reconstructions account for our findings.…”

“…These biases will be acute for short term temperature fluctuations and sub-regions within western Europe. Recent research has also demonstrated that methodological and analytical choices involved in the production of tree-ring-based temperature reconstructions affect the patterns present in those reconstructions (Büntgen et al, 2021). Variability with respect to analytical choices of researchers-all of which may be justifiable-can lead to biases in and differences among individual reconstructions even when they are based on overlapping source data (some of the same trees or trees from the same regions).…”

“…The fourth temperature time-series we included is a newly developed Northern Hemisphere tree-ring-based reconstruction (Büntgen et al, 2021). This time-series was constructed as part of a sizable community-based experiment in which the authors sought to determine how different methodological decisions affect tree-ring temperature reconstructions.…”

Impact of climate change on volcanic processes: current understanding and future challenges

“…Beyond direct observations, volcanic records and climate proxy records are also improving (e.g. Baldini et al, 2015;Lin et al, under review, Sigl et al 2021, Büntgen et al 2021. A better time-resolution of these records may for example help clarify the mechanisms and time lags associated with the impacts of changes in ice load or sea-level on magmatic processes.…”