Yale Environment
360
August 4, 2023
By Yale School of Environment
Was the Medieval
Era Warmer Than Now? New Tree Ring Study Offers Insight
![](images/images_08_09_2023/pexels-pixabay-355802.jpg)
A new study of tree rings in
Scandinavia is helping to resolve a longstanding question about the
Medieval Warm Period.
Past studies of tree rings had indicated that the Medieval period was
as warm or warmer than today, but climate models found otherwise.
Climate deniers have long pointed to the tree-ring data to suggest the
current period of warming is not without precedent.
The new tree-ring study, which used more precise methods than prior
research, agrees with the climate models.
For the study, researchers gathered data from 188 Scots pines, both
living and dead, in Sweden and Finland. While past studies largely
looked only at the width and density of rings, the new study analyzed
tree rings at a microscopic level, examining 50 million tree cells to
infer changes in temperature — cell walls tend to grow thicker in
hotter weather, which is why a darker layer of each ring forms in late
summer.
Researchers used the tree ring data to reconstruct summer
temperatures, finding that Scandinavia is now warmer than at any point
in the past 1,200 years. The findings, published in Nature, line up
with the climate models, highlighting the impact of human-caused
warming.
“This means that there are now two independent accounts of the
regional climate that both find lower temperatures during the
Medieval, providing new evidence that this phase was not as warm as
previously thought,” lead author Jesper Björklund, of the Swiss
Federal Institute for Forest, Snow, and Landscape Research, said in a
statement. “Instead, both show that the current warming is
unprecedented, at least in the past millennium.”
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