Back when CO2 levels were safe, a southwestern U.S. drought only lasted nearly 50 years

Scientists find evidence of Roman period megadrought

Almost nine hundred years ago, in the mid-12th century, the southwestern U.S. was in the middle of a multi-decade megadrought. It was the most recent extended period of severe drought known for this region. But it was not the first.

A cross section of wood shows the annual growth rings trees add with each growing season. Dark bands of latewood form the boundary between each ring and the next. Counting backwards from the bark reveals a tree's age. Credit: Daniel Griffin/Laboratory of Tree-Ring Research
The second century A.D. saw an extended dry period of more than 100 years characterized by a multi-decade drought lasting nearly 50 years, says a new study from scientists at the University of Arizona.