Long before the current drought or the continuing conversation about global warming, before the Dust Bowl, the climate in large portions of the American West was far drier than modern humans have become accustomed to.

The 19th and 20th centuries, ancient tree rings show, were a relative oasis of settlement-friendly weather.

The most reliable annual climate records go back just 80 years. For the longer view, scientists studied sections of more than 200 ponderosa pine and Douglas fir trees, some living, some dead, some almost 1,000 years old. Reading the tree rings, researchers stitched together a historical record of rainfall in El Malpais National Monument in New Mexico. (The researchers extracted pencil-thin wood cores from the living trees so as not to kill them.)

Widely spaced rings indicate wetter seasons; narrower rings indicate parched years. The resulting two-millenniums-plus record, from 137B.C. to 1992, is graphed here.