The United States’ drought-stricken Southwest and Great Plains should brace for the worst and most persistent drought in 1,000 years, according to a report out today by the Earth Institute at Columbia University.

The current extreme drought blanketing California and other parts of the West may be just the beginning. New research suggests that by 2050, the regions may enter the longest and driest period for a millennium — a product of natural weather cycles and man-made greenhouse gas emissions.

“The 21st century projections make [past] megadroughts seem like quaint walks through the Garden of Eden,” said Jason Smerdon, a co-author of the report and a climate scientist at the Lamont-Doherty Earth Observatory, part of Columbia’s Earth Institute.

Megadroughts last at least 10 years. Some researchers believe a megadrought contributed to the decline of the Anasazi, or ancient Pueblo people, in the Colorado Plateau in the late 13th century.

“The last time we’ve seen this kind of megadrought in these regions was in the 1400s. The projected conditions by the latter half of the 21st century will be as bad or worse than the severe megadrought periods of the past … worse than anything we’ve seen in the last 1,000 years,” Smerdon said.

This is the first study to conclude that the severity of this century’s drought could surpass even the worst megadroughts of the last millennium. Such a scenario would affect many more people because of the nation’s growing population. The current drought affects more than 64 million people, according to NASA.

“The report supports a growing body of evidence that links climate change to megadroughts,” said Juliet Christian-Smith, a climate scientist in the Oakland, California, office of the Union of Concerned Scientists, a group that works to develop solutions to global problems such as climate change. “Climate change and global warming will make bad droughts much worse.”

Lack of water, she said, is one of the effects of climate change that people feel the most.

Most information about past droughts comes from the study of tree rings from thousands of tree samples across the U.S., Mexico and parts of Canada.