A team of researchers at Columbia University has shown that long-term droughts in southwestern parts of North America and in southwestern parts of South America have occurred at the same time on multiple occasions over the past 1,000 years coinciding with La Niña events. In their paper published in the journal Nature Geoscience, the group describes how they used archival data and paleoclimate proxies (materials preserved in the geologic record that can be used to estimate climate conditions) to create a climate models.