Melting Arctic sea ice isn't just about polar bears: If temperatures continue to warm over the far north, a new study suggests, California could be in for a long dry spell.
A new profile of the climate at the end of the last ice age drawn from isotope studies on stalagmites in a cave known as Moaning Cavern records the onset of droughts that lasted for centuries in the central Sierra Nevada when Arctic temperatures rose and sea ice shrank.
Moisture dripping from the roof of the cave builds up over centuries, leaving layers like tree rings that contain trace elements from air, soil and rocks at the time of their formation. Like analyses of ice cores, different isotopes of these elements give clues to temperatures and precipitation levels in the distant past.
Some 15,000 years ago, when temperatures climbed out of the last ice age, dry conditions prevailed over California, the researchers found, and then shifted to a wetter climate when a cold episode returned about 2,000 years later.
"These are the only climate records of this type for California for this period when past global warming was occurring," said geologist Isabel Montañez of the University of California, Davis, who co-authored the study with graduate student Jessica L. Oster and others published online this month in Earth and Planetary Science Letters.
The findings reinforce other recent studies that link climate conditions in western North America with abrupt shifts in ocean and atmospheric conditions in the distant North Atlantic. Modelers connect the changes to shifts in the jetstream which drives Pacific storms over California when northern temperatures cool and farther north when temperatures warm.
"If this hypothesis is correct," warn the authors, "such linkages indicate that in response to global warming, effective moisture levels in the Sierra Nevada region may be reduced not only by enhanced evaporation due to warmer local temperatures, but also by reductions in Pacific moisture delivered to the region, thus strongly impacting water resources in a region already characterized by marginally sufficient water resources."
IMAGE: Credit: Isabel Montañez / Dept. of Geology, University of California, Davis
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