Rising global temperatures resulting from emissions of human origin could tip the southwestern United States into a period of prolonged extreme drought seen before only in distant geological history, a new study suggests.

Valles Caldera National Preserve

Researchers dug deep into the region’s climate history by studying a 270-foot core of lake sediment taken from the Valles Caldera, a volcanic depression in northern New Mexico. Data extracted from the core revealed “mega-droughts” in the region lasting as long as a thousand years.

For parallels to the planet’s current climate, the researchers focused on interglacial periods, when ice ages caused by small irregularities in the Earth’s orbit around the sun gave way to periods of warmth and glacial retreat. The current epoch, the Holocene, is the most recent interglacial period.



If the current epoch followed past trends, the Southwest would eventually enter a cooler, wetter phase, the researchers found. But that was without considering changes in the global climate that are expected to arise from steadily rising concentrations of carbon dioxide and other greenhouse gases.

This added warmth could tip the Southwest into an era of continued severe drought potentially lasting a millennium or more, said Peter Fawcett, a climate scientist at the University of New Mexico in Albuquerque who led the study.

“We won’t know for sure if it happens again until we get there,” Dr. Fawcett told Nature News. “But we are certainly increasing the possibility of crossing a critical threshold to severe and lasting drought conditions.”

“The scary thing is that we seem to be very close to this point again,” he added.

The study appears in this week’s edition of the scientific journal Nature.