Periodic events called El Niño and La Niña alter the circulation of warmer and cooler water in ocean currents, leading to changes in climatic patterns across large regions. (earthjournalism.net)
Fritts, H.C. (1991) Reconstructing Large - scale Climatic Patterns from Tree - Ring Data, The University of Arizona Press. (mpra.ub.uni-muenchen.de)
1991 H.C. Fritts, Reconstructing Large - Scale Climatic Patterns from Tree Ring Data. (history.aip.org)