By Gary Thomas
The journal, Nature Climate Change has published a study related to climate reconstruction in northern Europe over the past 2,000 years. An international research team has calculated the cooling trend over the period. These findings are important for the present climate policy.
The reconstruction provides a high-resolution representation of temperature patterns in the Roman and Medieval warm periods, but also shows the cold phases that occurred during the Migration Period and the later Little Ice Age. Illustration/Copyright: Institute of Geography, JGU
The international research team used measurements of tree density of sub-fossil pine trees that originated from the Finnish Lapland. Scientists from the Johannes Gutenberg University Mainz (JGU) were part of the study, and they developed a reconstruction dating back to 138 BC. It showed the pattern of temperature that existed in the Roman and Medieval warm periods, as well as the cold phases that took place during the Migration Period and the Little Ice Age period.
The researchers found that the temperature estimates of the Roman era and the Middle Ages were too low. They demonstrated that the change in climate was towards climate cooling over the past 2000 years.
The growth rings of trees provide an indication of the climatic conditions during the earlier periods. In the Finnish Lapland, trees collapsed into the lakes, where they stayed in a preserved state for long periods stretching into thousands of years. The researchers studied the sub-fossil pine trees. The summer temperature in an area correlates with the density of the tree rings. The researchers reconstructed the data to represent the temperature patterns during the period. They showed a cooling trend of -0.3°C per millennium, which occurred due to the increase in distance between the sun and the Earth, and the changes in the position of the sun.
Till now, global warming has been less than 1°C. The cooling trend, which may seem to be insignificant, cannot be neglected. The study suggests that the long-term cooling trend may have been underestimated by the Intergovernmental Panel on Climate Change in its large-scale climate reconstruction.