2023-08-02 17:15:17
Ongoing climate change has already produced warming “unprecedented in the last 1,200 years”. Even “the Medieval Warm Period was colder than previously thought” and therefore cooler than the phase we live in. This is, in summary, the conclusion of an international study coordinated by Marco Carrer of the University of Padua and Georg von Arx of the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL). A response put on paper in the magazine ‘Nature’ and which comes to us from the trees: to be precise from 188 Scots pines, whose rings precisely tell the ‘meteorological history’ of about 1,200 years.
‘The Middle Ages and subsequent centuries were also turbulent from a climatic point of view,’ the scientists recall. “Not only did the famous Little Ice Age occur, but its opposite,” the Medieval Warm Period as well. This was a phase of unusual warming, but has always puzzled researchers as produced so far with tree rings seemed to indicate even higher temperatures than today. However, there was no plausible physical explanation capable of justifying this exceptional warming. Indeed, climate models indicate mild but not mild temperatures for the Medieval Warm Period so high”.
“Previous climatic reconstructions – explains Carrer of the UniPD Department of Land and Agro-forestry Systems – were based on the width or density of the tree rings. These measurements depend a lot on the temperature, but sometimes other factors take over that can influence the width or density of a ring”. Now, “together with other researchers, we have produced a new climate reconstruction based on an innovative and particularly precise method for extracting information on past temperatures from trees”. And “unlike previous work, the new results lead to the same conclusion as climate models: The Medieval Warm Period, at least for Scandinavia, where the trees studied come from, was colder than previously thought. Current warming is therefore probably outside the range of natural temperature fluctuations over the past 1,200 years.”
For this study – describes a note from the University of Padua – a new method was used which allows the thickness of the cell walls of the wood to be measured directly. “Every single cell in each ring – underlines Jesper Björklund of the WSL, first author of the work – records climatic information relating to the moment of its formation. By analyzing hundreds, sometimes thousands of cells per ring, it is possible to obtain extraordinarily precise climatic information”.
For this investigation, therefore, the researchers measured the cell walls of 50 million cells from 188 Scots pines (Pinus sylvestris), both alive and dead, whose rings cover a period of about 1,200 years. Based on the measurements taken, the scientists reconstructed the summer temperatures in the region and compared them both with simulations of regional climate models and with previous reconstructions based on annual ring density. “The result is clear”, they decree: “The temperatures of the models and those reconstructed from the woody cells coincide”. Therefore “now – comments von Arx – there are two independent sources that indicate that medieval temperatures were lower than previously thought. On the contrary, it is confirmed that the current warming is unprecedented, at least in the last millennium”.
If on the one hand “these results contribute to confidence in the projections of climate models”, on the other, warns Carrer, they underline “the key role of human activities in determining the warming phase we are currently experiencing”.
#hot #years