California’s five-year drought, which has effects as diverse as an increase in devastating wildfires and the normalization of brown lawns, could become the region’s “new normal,” according to researchers.
The study, published in Nature.com journal Scientific Reports, looked at periods over the past 10,000 during which natural climatic forces—like sun spots, a slight change in earth’s orbit or a decrease in volcanic activity—warmed the region through a process called radiative forcing. This warming set off periods of dryness that lasted hundreds or thousands of years.
Now, man-made greenhouse gases are causing a similar warming effect and could lock the region in a centuries-long drought, according to the study led by UCLA professor Glen MacDonald.
“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.”
Not only could radiative forcing produce drought-like conditions, the warming also was closely tied to long-term changes in the Pacific Ocean’s surface temperatures. When ocean temperatures change, the El-Niño-La-Niña cycle is affected, and El Niño storms, which increase precipitation in California, subside and give way to La Niña systems, which suppress rain in the region.
One period of dryness lasted from about 950 to 1250 A.D. due to radiative forcing and warming caused by decreased volcanic activity and increased sunspots. La Niña gripped the region during this period.
A period of warming mixed with a similarly inconsistent El-Niño-La-Niña cycle could have disastrous effects on wild plant life, MacDonald said.
“I think we would find a way to keep our cities going through prolonged drought, but we’re not going to engineer a way to conserve or preserve the ecosystems of the state,” MacDonald said. “We can’t save our huge expanses of oak woodlands, or our pine and fir forests, or high-elevation alpine ecosystems with irrigation projects like we might our orchards and gardens. I worry that we will see very different wildlands by the end of this century.”
Researchers studied 2-inch-wide and 10-foot-deep sediment samples in the Seirra Nevada and Kermin Lake area. By studying this sample in third-of-an-inch segments and correlating findings with previous studies of California’s climate history, researchers were able to create the most detailed record of California’s dry period ever compiled, MacDonald said.
“Climate models today have a challenging time predicting what will happen with Pacific sea-surface temperatures in the face of climate change,” MacDonald said. “We hope that our research can improve that.”
