Tree rings reveal El Nino history

NEW YORK, May 27 (UPI) -- Scientists say tree-ring data from the American Southwest is providing a 1,100-year history of the global climate effects of the El Nino and La Nina cycles.

Scientists have speculated that a warming planet will make those periodic shifts in Pacific Ocean temperatures that affect weather around the globe more volatile and say the tree-ring data backs up that theory, a release by Columbia University said Friday.

Researchers at Columbia say an analysis of the tree rings shows a 50- to 90-year cycle of waxing and waning El Nino intensity proving that when the Earth warms, the climate acts up.

The tree-ring analysis corresponded to several other records including instrument readings for Pacific Ocean surface temperatures, isotope analysis of modern and relic corals from around the Pacific, and other climate reconstructions, researchers said.

"Our work revealed that the towering trees on the mountain slopes of the U.S. Southwest and the colorful corals in the tropical Pacific both listen to the music of El Nino, which shows its signature in their yearly growth rings," lead study author Jinbao Li said.

Those growth rings reveal a pattern, the researchers said, as the variance between warm El Nino and cool La Nina conditions becomes more pronounced in periods when the background temperature is warmer, and less so in cooler periods.