During the Little Ice Age (LIA; covering approximately the fifteenth through the eighteenth centuries), northern South America experienced about 10 percent more rainfall than during the twentieth century, according to Reuter et al.

The authors analyzed two new records of oxygen isotopes (which track precipitation levels) from cave formations in northeastern Peru. They attribute the higher rainfall in northern South America during the LIA to cooler spring sea surface temperatures in the tropical North Atlantic.

Furthermore, the authors note that some studies have shown that during the twentieth century, a significant amount of rainfall variability in northern South America was related to the El Niño-Southern Oscillation (ENSO), with higher rainfall occurring during La Niña conditions.

However, the authors determine that the ENSO was probably not as significant an influence on rainfall during that time period as it is now.

The authors suggest that the results point to a need to reevaluate some ideas about hydroclimate change over South America during the past millennia.

The research is published in Geophysical Research Letters. Authors: Justin Reuter, Lowell Stott, and Deborah Khider: Department of Earth Sciences, University of Southern California, Los Angeles, California, USA; Ashish Sinha: Department of Earth Sciences, California State University, Carson, California, USA; and Hai Cheng and R. Lawrence Edwards: Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota, USA.