Clues from prehistoric droughts and arid periods in California show that today’s increasing greenhouse gas levels could lock the state into drought for centuries, according to a study led by UCLA professor Glen MacDonald.

The study, published today in the Nature.com journal Scientific Reports, looked at how natural climatic forces contributed to centuries-long and even millennia-long periods of dryness in California during the past 10,000 years. These phenomena—sun spots, a slightly different earth orbit, a decrease in volcanic activity—intermittently warmed the region through a process called radiative forcing, and recently have been joined by a new force: greenhouse gases.

As long as warming forces like greenhouse gases are present, the resulting radiative forcing can extend drought-like conditions more or less indefinitely, said MacDonald, a distinguished professor of geography and of ecology and evolutionary biology.

“Radiative forcing in the past appears to have had catastrophic effects in extending droughts,” said MacDonald, an international authority on drought and climate change. “When you have arid periods that persist for 60 years, as we did in the 12th century, or for millennia, as we did from 6,000 to 1,000 B.C., that’s not really a ‘drought.’ That aridity is the new normal.”

Researchers tracked California’s historic and prehistoric climate and water conditions by taking a sediment core in the Sierra Nevada mountains. They pulled a 2-inch-wide, 10-foot-deep cylinder of sediment from the bottom of Kirman Lake and analyzed it in third-of-an­-inch sections, creating the most detailed and continuous paleoenvironmental record of California.

The team correlated their findings with other studies of California climate history, and for the first time, united all the studies and cross-referenced them with histories of the Pacific Ocean’s temperature taken from marine sediment cores and other sources.

What they found was not only that periods of increased radiative forcing could produce drought-like conditions that extended indefinitely, but that these conditions were closely tied to prolonged changes in Pacific Ocean surface temperatures.

While the urban areas of California may find a way to deal with this, but the agriculture sector of the state is completely f%$#ed.