‘Unusually active’ El Nino pattern could increase flood, drought frequency

New research of tree rings suggests that the El Nino Southern Oscillation weather pattern affecting the Pacific Ocean has been “unusually active” in the late 20th century and a meteorology expert suggests this could increase the frequency of floods and droughts.

Scientists at the Honolulu, Hawaii-based International Pacific Research Center (IPRC) have compiled 2,222 tree-ring chronologies from the last 700 years, according to a University of Hawaii at Manoa press release.

“Many climate models do not reflect the strong ENSO response to global warming that we found,” University of Hawaii meteorology professor Shang-Ping Xie stated in a press release July 2.

“This suggests that many models underestimate the sensitivity to radiative perturbations in greenhouse gases. Our results now provide a guide to improve the accuracy of climate models and their projections of future ENSO activity. If this trend of increasing ENSO activity continues, we expect to see more weather extremes such as floods and droughts.”

Xie and Jinbao Li, assistant professor of geography at the University of Hong Kong, co-authored a paper, titled El Niño Modulations over the Past Seven Centuries, and published in the July issue of Nature Climate Change. Xie is currently on leave from University of Hawaii as the Roger Revelle Chair in Environmental Science at the Scripps Institution of Oceanography at the University of California at San Diego.

El Nino refers to several weather patterns associated with sea surface temperature changes in the Pacific Ocean, including a warming of the ocean near South America, according to the California Department of Fish and Wildlife.

“A strong El Nino is often associated with flooding rains and warm weather in Peru, drought in Indonesia, Africa, and Australia, torrential downpours and mudslides in southern California, a mild winter in the northeast and fewer hurricanes in the southeast,” according to the California Fish and Wildlife department website.

The University of Hawaii noted in its July 2 press release that the El Nino Southern Oscillation varies over decades and centuries.

“Instrumental records are too short to determine whether any changes seen recently are simply natural or attributable to man-made greenhouse gases,” according to the press release. “Reconstructions of ENSO behavior are usually missing adequate records for the tropics where ENSO develops.”

However, the “proxy records” compiled by the IPRC team “indicate that ENSO was unusually active in the late 20th century compared to the past seven centuries, implying that this climate phenomenon is responding to ongoing global warming.”

IPRC is part of the School of Ocean and Earth Science and Technology at the University of Hawaii at Manoa, which is based about three kilometres north of the tourist resort of Waikiki. Its researchers study climate variation in the Asia-Pacific region and how global climate changes may affect the region.

The tree ring research was funded by the U.S. National Science Foundation, the National Basic Research Program of China, the National Oceanic and Atmospheric Administration, the Japan Agency for Marine-Earth Science and Technology, two Chilean government research funds, Argentina’s CONICET research and development agency and the Inter American Institute for Global Change Research (AIA).

In addition to Li and Xie, contributors of the paper included Edward R. Cook, Mariano S. Morales, Duncan A. Christie, Nathaniel C. Johnson, Fahu Chen, Rosanne D’Arrigo, Anthony M. Fowler, Xiaohua Gou and Keyan Fang.