European dry spells during the past two decades have been more severe than others in the past 2,110 years due to anthropogenic climate change, reports a study published online this week in Nature Geoscience.
Prolonged droughts can have profound environmental and social effects; the European heat waves in the summers of 2003, 2015 and 2018 put pressure on food and health systems across the continent. However, understanding the causes and frequency of these droughts and how they compare to droughts in the past is hampered by a lack of reliable drought records prior to the keeping of high-quality meteorological observations.
Ulf Buentgen and colleagues reconstruct the timing and severity of European droughts over the last two millennia by analysing 27,080 growth rings from 147 oak trees from central Europe that grew over the past 2,110 years. They measure the oxygen and carbon isotope composition of the growth rings, which systematically change as the trees respond to water and heat stress. By combining records from living trees and logs pulled from old buildings and archaeological sites, they were able to determine whether a drought occurred in any particular year starting from 75 bce. They show that the high year-on-year frequency of European droughts in the past two decades is unprecedented, even compared to pronounced historical droughts during the Late Antique Little Ice Age (around the sixth century of the Common Era) and Renaissance (early sixteenth century of the Common Era).
The authors suggest that atmospheric circulation over the continent and the position of the jet stream represent the dominant drivers of historical drought occurrence in the region. Ongoing changes in these circulation patterns due to climate change, while complex, are likely to be responsible for the recent increase in dry, hot European summers.
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