A team led by scientists at the University of Arizona is connecting the ongoing drought to an expansion of the tropics caused by climate change.
The group includes UA tree-ring researchers, who say their study has implications for the Sonoran Desert. It sits just north of the tropical belt, along with the Mohave and Sahara Deserts. According to study co-author Valerie Trouet, the northern edge of the tropics has moved up to 4 degrees north and 4 degrees south of its standard location of 30 degrees north latitude.
"So that means that the dry regions at the edge of the tropics is becoming larger," she said. "That's why in the Northern Hemisphere, you'll find dry regions further north of where they were before."
Trouet says changes in the Earth's climate system affect the movement of the tropics.
The team used the annual rings of trees from five different locations across the Northern Hemisphere to track the tropical belt's movement from the year 1203 to 2003. Each annual growth ring of a tree reflects the climate in the tree's location that year.
The team's research appears in the online publication Nature Geoscience.