Tree rings have helped climatologists build a picture of severe droughts and wet periods across Europe and the Mediterranean over the past 2,000 years.
And the study will help climatologists predict future weather patterns.
Until now researchers have had to rely on historical records which only described weather events in particular locations and did not provide climate data that many current modeling studies needed.
But by using the ring growth from trees, scientists have built up a comprehensive atlas to provide a bigger picture of events that affected the whole continent and its neighbours in North Africa and the Middle East.
Together with two previous drought atlases covering North America and Asia, the Old World Drought Atlas significantly adds to the historical picture of long-term climate variability over the Northern Hemisphere.
It could even help predict future conflicts such as the drought in the Middle East that led to the Syrian civil war in 2010.
It also shed light on he influence from the North Atlantic Oscillation, one of the primary sources of climate variability affecting patterns in Europe, because of its role in making Europe north of the Alps wetter and a drier to the south.
This climate phenomena is a variation in North Atlantic sea-surface temperatures that until now has not been tracked long enough to tell if it is a transitory event, caused by mankind or a natural long-term oscillation.
By combining the three atlases, climatologists and climate modelers may also discover other sources of internal climate variability that are leading to drought and wetness across the Northern Hemisphere.
The Old World atlas also expands scientists’ understanding of climate conditions during historic famines.
An unusually cold winter and spring are often blamed for a 1740-1741 famine in Ireland but rainfall well below normal during the spring and summer of 1741 could also have played a part.
The atlas shows how the drought spread across Ireland, England and Wales.
The atlas also tracks the reach of the great European famine of 1315-1317, when historical documents describe how excessive precipitation across much of the continent made growing food nearly impossible.
The atlas tracks the hydroclimate across Europe and shows its yearly progressions from 1314 to 1317 in detail, including highlighting drier conditions in southern Italy, which largely escaped the crisis.
Edward Cook, cofounder of the Tree Ring Lab at Columbia University’s Lamont-Doherty Earth Observatory said: “The Old World Drought Atlas fills a major geographic gap in the data that’s important to determine patterns of climate variability back in time.
“That’s important for understanding causes of megadroughts, and it’s important for climate modelers to test hypotheses of climate forcing and change.
“You can’t get that from one spot on a map. That’s the differentiator between the atlas and all these wonderful historic records – the records don’t give you the broad-scale patterns.”
Richard Seager added: “Climate variability tends to occur within patterns that span the globe, creating wet conditions somewhere and dry conditions somewhere else
“By having tree ring-based hydroclimate reconstructions for three northern hemisphere continents, we can now easily see these patterns and identify the responsible modes of variability.”
The study was published in the journal Science Advances
