Scientists examined tree rings from the past 1,200 years and found that the current pattern of global warming is unprecedented during the Common Era.
This finding has long been confirmed by models of climate change examining paleoclimate records and other earth system models, which indicated that the current climate is warmer than it’s otherwise been during the Common Era. However, dendrochronology — the science of studying tree rings — has often conflicted with this finding, with tree-rings pointing to warmer temperatures during the Medieval Climate Anomaly (950-1250 CE).
The recent study, conducted by researchers from the Swiss Federal Institute for Forest, Snow and Landscape Research WSL and published in Nature, aligns the results of studying tree rings with the findings from other climate change models.
Using a new method, the researchers measured the cell wall thickness of 50 million cells in the tree rings of 188 living and dead Swedish and Finnish Scots pines. Together, the tree rings examined covered 1,170 years of recent history.
“Previous reconstructions are based on the width or density of the annual tree rings," explains study co-author Georg von Arx. "Both are very much dependent on temperature, but sometimes other factors play a role in how wide or dense a tree ring gets."
The scientists then used their measurements to reconstruct the summer temperatures in the Fennoscandian Peninsula. They found that the current climate is, in fact, “substantially warmer” than that of the medieval period.
“There are now two independent accounts of the regional climate that both find lower temperatures during the Medieval,” study lead author Jesper Björklund said. “Both show that the current warming is unprecedented, at least in the past millennium, and emphasize the role of greenhouse gas emissions on Scandinavian temperature variability."
Study author von Arx reiterated the importance of this new alignment between the conclusions of dendrochronology and that of other climate models. "This is critical because such reconstructions are considered when evaluating the accuracy of climate models. If the previous reconstructions were used as a benchmark, this would significantly downplay the human influence on current climate warming and reduce confidence in model projections," says von Arx.
Sources: Nature, 2023; Nature, 2019; Phys.org