Dr. Philipp Lengsfeld
Primary source: Rydval et al. (2017)
An international group of researchers used tree rings as a proxy to reconstruct summer temperatures for Scotland, going back as far as 1200 AD. First author Milos Rydval is currently a researcher at the Czech university of Life Sciences, focusing on Forestry and Wood Sciences.
The study is using both ring widths as well as blue intensity (reflection imaging of tree ring cores for reconstruction) for their reconstruction. The obtained temperatures were checked and compared to historic records containing information about years with famine or droughts. The study sample contains 44 Scot pine trees from Northern Cairngorms National Park as well as 109 subfossil trees. As a calibration reference, the time period of 1901-2009 was used (calibration (1901–1954), verification (1955–2009)).
The key result of the work of Rydval et al. is a reconstruction of the July-August temperatures in that region across the timeframe 1200 till 2010 (Fig. 5 of original publication). Rydval et al. documented the warm periods in the 14th century as well as the 16th century. Temperature changes of up to 3K where recorded across timeframes between 60 – 120 years both as cooling and warming. The error range is, of course, even broader. The warmest 5 years within the reconstruction time were according to the authors 1284, 1285, 1307, 1310 and 1282, 2010 ranks #6, and 2003 #7. Based on decade 2001-2010 ‘only’ ranks as third warmest. The coldest decade was 1691-1700. The reconstruction matches with extreme cold years according to historical accounts.
Although there is some limitation within this reconstruction (e.g. due to low replication and age structure), the authors conclude that within the context of the reconstruction uncertainty, recent summertime warming is not significantly more pronounced than past reconstructed warm periods in the region studied. Also, they find that warm/cold summer temperatures coincide with high/low pressure anomalies centered over the North Sea.
This work documents diligently the temperature of a region (northern Europe/Scotland) for almost the last millennium. Results show that recent developments do not present anything outside previous climate changes in that region of northern Europe. Scientific and political considerations probably should focus more on the understanding, modelling, and prediction of regional climate effects. As the complexity of regional modelling should be somewhat lower than that of global climate modellings better insights in the main drivers of regional climate should be obtained, which would improve models and the understanding considerably. The data presented by Rydval et al. should be able to serve as a reliable ground truth for regional modelling.
Rydval et al. Reconstructing 800 years of summer temperatures in Scotland from tree rings Clim Dyn 49:2951–2974 (2017)