In 2012, an international team of scientists published a study, where they reconstructed climate in northern Europe for the past 2 000 years. For the first time, the cooling trend was calculated precisely. Read more about this interesting discovery!
A research team, under the leadership of Professor Dr. Jan Esper from Johannes Gutenberg University in Mainz, used a tree-ring density to produce a climate reconstruction reaching back to 138 BC. Researchers used measurements from sub-fossil pine trees originating from Finnish Lapland region. It was first time, when long-term climate cooling trend, over the past two millennia, has been demonstrated.
Jan Esper said about their results published in Nature Climate Change journal:
“We found that previous estimates of historical temperatures during the Roman era and the Middle Ages were too low. Such findings are also significant with regard to climate policy, as they will influence the way today’s climate changes are seen in context of historical warm periods.”
How did the Romans grow grapes in England?
Researchers examined tree-ring density profiles from sub-fossil pine trees in northern Scandinavia. As we know, the climate in Scandinavia is very cold. The landscape was formed many times by glacier, and in consequence many lakes were created. Interestingly, in such a place trees were often collapsing into one of the thousands lakes, where they remain very well preserved up to now.
Scientists from Germany, Finland, Scotland, and Switzerland were able to create a sequence reaching back to 139 BC (see graph below).
A graph shows that the Britain of 2 000 years ago and Medieval period of 1000 years ago experienced a lengthy period of hotter summers than today. The Medieval Warm Period was already known, while the toga-wearing Roman times when temperatures were apparently 1 deg C warmer was quite a new discovery.
In addition, the graph presents very clear cooling trend that occured for last 2000 years. Scientists demonstrated that this trend involves a cooling of -0.3°C per millennium due to gradual changes to the position of the sun and an increase in the distance between the Earth and the sun.
Professor commented this result in the following way:
“This figure we calculated may not seem particularly significant. However, it is also not negligible when compared to global warming, which up to now has been less than 1°C. Our results suggest that the large-scale climate reconstruction shown by the Intergovernmental Panel on Climate Change (IPCC) likely underestimate this long-term cooling trend over the past few millennia.”
Source: Esper J., DC. Frank, M. Timonen, E.Zorita, RJ. S. Wilson, J. Luterbacher, S. Holzkämper, N. Fischer, S. Wagner, D. Nievergelt, Anne Verstege and Ulf Büntgen. 2012. Orbital forcing of tree-ring data. NATURE CLIMATE CHANGE, VOL 2.
Main photo: Lake in Finland. Photo credit: Rafal Chudy