Its main author, Columbia biologist Edward Cook, has already carried out similar projects using trees to create chronological(按顺序排列的) maps of drought in Asia and North-America. He believes that combining the three atlases could throw light on the global causes of drought and climate change.

　　The study, for instance, gave special attention to the importance of one of such causes,the North Atlantic Oscillation(涛动) , in affecting climate patterns in Europe,and specifically in making Europe wetter north of the Alps and drier south of them.

　　The OWDA also helped analyse historical events from a climatic perspective. For

　　instance, the 1740-174lfamine in Ireland had so far been explained by an unusually

　　cold winter and spring, but the atlas shows that unusually low rainfall over the spring and summer of 1741 could also have played a role. Finally this made growing food nearly impossible and caused a continent-wide famine.

　　A better grasp of these processes could even make it possible to predict future

　　famine, unrest and conflict.

　　Cook said, 64The Old World Drought Atlas fills a major geographic gap in the data that's important to determine patterns of climate changes in time. That's important for understanding causes of many droughts, and it's important for climate modelers to test hypotheses(偎说) of climate forcing and change.