At a site in Basalt Lake, Greenland, researchers demonstrate how to collect a sediment sample, which reveals the geologic history of the area in layers. The sample in this study was extracted from Kirman Lake in California. (Photo credits: Hannes Grobe/ AWI)
Evidence of prehistoric droughts indicate current levels of greenhouse gases could lead to century-long droughts, according to researchers at the University of California, Los Angeles.
Led by UCLA professor Glen MacDonald, the study examined how radiative forcing—a climatic warming process involving sun spots, changes in the earth’s orbit, and decreases in volcanic activity—has led to extended, dry climates in the past. Today, the addition of greenhouse gases could lead to periods of persistent aridity.
The scientists studied Kirman Lake in northern California, a lake whose geologic record is sensitive to climate change. The team created the most detailed record of California’s climactic history to date by extracting a two-inch wide, ten-foot deep sediment core from the bottom of Kirman Lake. They then analyzed the sediment sample one-third inch at a time to study California’s prehistoric climate. Years of studying this record of California’s history revealed periods of more frequent wildfires, eras with increased vegetation, periods of shallow water, and changes in the lake’s salinity.
Like previous studies of California’s climate, they found that increased radiative forcing created historic droughts during the mid-Holocene and medieval periods. For the first time, however, the researchers also combined their findings with studies of marine sediment samples, discovering that periods of aridity occurred alongside changes in the surface temperature of the Pacific Ocean.
Fluctuations in the temperature of the Pacific Ocean are linked to El Niño and La Niña weather patterns. The study found that during dry periods in California’s history, La Niña conditions prevailed with lowered ocean precipitation, suggesting a connection between ocean conditions and California’s climate. Moister periods during the Holecene period coincided with El Niño conditions on the Pacific as well as the decline of civilizations in Egypt and Mesopotamia. These findings suggest El Niño and La Niña conditions also have global consequences.
The study gives a peek into California’s future. MacDonald foresees less forest land, more grassland and desert, rising temperatures, less precipitation, increased fires, and indefinite drought as radiative forcing continues along with rising levels of greenhouse gases. While the future climate of California may not exactly mirror the millennia of dryness in the past, and a century-long drought is not inevitable, the evidence is concerning, especially as California continues to experience severe droughts and wildfires. The team hopes their research can improve current climate models and more accurately predict the future of California’s ecosystem.
References:
1. UCLA. (2016, September 15). Pacific Ocean’s response to greenhouse gases could extend California drought for centuries. ScienceDaily. Retrieved September 18, 2016 from www.sciencedaily.com/releases/2016/09/160915131524.htm
2. Glen M. MacDonald, Katrina A. Moser, Amy M. Bloom, Aaron P. Potito, David F. Porinchu, James R. Holmquist, Julia Hughes, Konstantine V. Kremenetski. Prolonged California aridity linked to climate warming and Pacific sea surface temperature. Scientific Reports, 2016; 6: 33325 DOI:10.1038/srep33325
3. AWI, H. G. (2010, February 12). Basalt Lake Coring [Palaeoclimate archives: Sediment sampling with a piston coring system from a raft, Basalt lake, Greenland]. Retrieved September 22, 2016, from https://commons.wikimedia.org/wiki/File:Basaltlake-coring_hg.jpg