With new methods of reconstruction, climate researchers in Bern have been able to demonstrate that some 9,000 to 5,000 years ago, the Mediterranean climate was considerably warmer than previous studies had suggested. Among other things, previous concerns regarding the reliability of climate models could thus be dispelled.
Climate reconstructions are necessary because reliable measurement data are only available for the last 150 years. For this reason, research on past climate change uses so-called ‘proxies’. These are indicators with which it is possible to reconstruct temperatures in the past. A widespread reconstruction method examines pollen which is embedded in lake sediments. From the composition of this pollen, it is possible to determine the plant species which occurred at a particular location in the past – and since the temperatures that the individual species require are also known, it is possible to reconstruct the temperature conditions for the period in question.
With new methods of reconstruction, climate researchers in Bern have been able to demonstrate that some 9,000 to 5,000 years ago, the Mediterranean climate was considerably warmer than previous studies had suggested. Among other things, previous concerns regarding the reliability of climate models could thus be dispelled.
Climate reconstructions are necessary because reliable measurement data are only available for the last 150 years. For this reason, research on past climate change uses so-called ‘proxies’. These are indicators with which it is possible to reconstruct temperatures in the past. A widespread reconstruction method examines pollen which is embedded in lake sediments. From the composition of this pollen, it is possible to determine the plant species which occurred at a particular location in the past – and since the temperatures that the individual species require are also known, it is possible to reconstruct the temperature conditions for the period in question.
It is on the analysis of pollen – including from silver fir trees in Italy – that the only previously available quantitative summer temperature reconstructions for the northern Mediterranean region were based on. These suggested that the mid-Holocene (9,000 to 5,000 years ago) had been an exceptionally cold period. However, it is also possible to examine past climate using models. In contrast to the pollen analyses, model-based simulations indicated that summer temperatures should have been warmer during this period.
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Image: Remains of a midge larva. The distribution of these microfossils in lake sediments provides information on past temperatures.
Credit: © Oliver Heiri / University of Bern
