A warning from ancient tree rings: The Americas are prone to catastrophic, simultaneous droughts
https://www.sciencemag.org/news/2019/12/warning-ancient-tree-rings-americas-are-prone-catastrophic-simultaneous-droughts
Source: By Paul Voosen, Science Magazine.
Excerpt: For 10 years, central Chile has been gripped by unrelenting drought. With 30% less rainfall than normal, verdant landscapes have withered, reservoirs are low, and more than 100,000 farm animals have died. The dry spell has lasted so long that researchers are calling it a “megadrought,” rivaling dry stretches centuries ago. It’s not so different from the decadelong drought that California, some 8000 kilometers away, endured until this year. By analyzing tree ring records, scientists have now found evidence that such tandem droughts are more than a coincidence: They are surprisingly common over the past 1200 years, and they may often share a common cause—an abnormally cool state of the eastern Pacific Ocean known as La Niña. ...Nor is it clear how the drought patterns will change as climate warms. A warming atmosphere alone seems certain to make megadroughts more frequent, especially in the Southwest. But scientists remain divided on how climate change will affect the El Niño-La Niña cycle. Models suggest El Niño will dominate, but in the past few decades, La Niña has seemed to be more frequent. ...As bad as the drought in Chile is today, it barely qualifies as a megadrought when compared with the medieval ones, which were longer and more severe. Clearly, there was something about that period that switched off in recent centuries, Cook says. If that pattern somehow came back, with greenhouse warming amplifying it, Cook says, “then things could get quite catastrophic.”....
Source: By Paul Voosen, Science Magazine.
Excerpt: For 10 years, central Chile has been gripped by unrelenting drought. With 30% less rainfall than normal, verdant landscapes have withered, reservoirs are low, and more than 100,000 farm animals have died. The dry spell has lasted so long that researchers are calling it a “megadrought,” rivaling dry stretches centuries ago. It’s not so different from the decadelong drought that California, some 8000 kilometers away, endured until this year. By analyzing tree ring records, scientists have now found evidence that such tandem droughts are more than a coincidence: They are surprisingly common over the past 1200 years, and they may often share a common cause—an abnormally cool state of the eastern Pacific Ocean known as La Niña. ...Nor is it clear how the drought patterns will change as climate warms. A warming atmosphere alone seems certain to make megadroughts more frequent, especially in the Southwest. But scientists remain divided on how climate change will affect the El Niño-La Niña cycle. Models suggest El Niño will dominate, but in the past few decades, La Niña has seemed to be more frequent. ...As bad as the drought in Chile is today, it barely qualifies as a megadrought when compared with the medieval ones, which were longer and more severe. Clearly, there was something about that period that switched off in recent centuries, Cook says. If that pattern somehow came back, with greenhouse warming amplifying it, Cook says, “then things could get quite catastrophic.”....