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Scientific evidence – For more than 1000 years it has never been as warm in Scandinavia as it is now – News

4 August 2023

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Research shows that in the Middle Ages there was no climate anomaly comparable to today’s global warming.

The Research Institute for Forest, Snow and Landscape (WSL) found out from annual rings on trees that it has never been warmer in the last 1200 years than it is today, at least not in Scandinavia.

Legend:

The researchers analyzed wood from trees preserved in mountain lakes.

SRF/zvg WSL/Hakan Grudd

To do this, the researchers measured the cell wall thickness of the wood cells in tree rings. “Unlike in the past, we were also able to measure the cell walls, the building blocks of the tree rings. It has been shown that the thickness of the cell walls – the strengthening of the building blocks – is closely related to the temperatures,” says study leader Georg von Arx from the WSL in Birmenstorf.

The cell walls of 50 million wood cells from living and dead Scots pines from Scandinavia and Finland were examined.

No climate anomaly in the Middle Ages

Systematic weather and climate data have only existed for around 150 years. “The results from the corresponding cell walls agree closely with the data we have from the last 150 years,” says von Arx.

The researchers therefore assume that the results from the cell walls of earlier times, when people had not yet described the weather and climate, are also meaningful. “We were thus able to reconstruct the temperatures in times for which there is no historical data,” says von Arx.

Microscopic view of cell walls in tree growth rings

As a result, for example, the assumption that there was an extraordinary warm period, a so-called climate anomaly, in the Middle Ages can be refuted. This climate anomaly in Scandinavia was assumed based on conventional tree ring analyses.

Conventional annual ring studies of trees revealed a so-called Medieval Warm Period, especially in the northern hemisphere. With their study, the researchers wanted to look for the reasons for this climate anomaly. This riddle was solved with the available research: The Medieval Warm Period was not as warm as assumed – at least not in Scandinavia. It was in no way comparable to today’s global warming.

unprecedented global warming

If you believe the newly collected data, this suspected climate anomaly did not exist, at least in Scandinavia.

The current global warming is unprecedented, at least for Scandinavia.

The researchers can therefore say conclusively that it is warmer today than it was 1,200 years ago. The following can be read from this for current climate research, as von Arx says: “The current global warming is unprecedented, at least for Scandinavia.”

Data confirm the climate models

The tree ring data from the study confirm the data from existing climate models. They see the increase in CO₂ as the main driver for the current warming.

It is a graph showing temperature variations between the years 1450 and 1556.

Since the increase in the CO₂ concentration has been proven to be man-made, the current warming must also be man-made, according to the researchers. “Other interpretations are unlikely because our very precise reconstruction for the period before industrialization – i.e. before human influence – never finds periods anywhere near as warm as today, not even in the medieval warm period,” says von Arx.