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Study finds La Ninas lasting longer, intense El Ninos likely to follow

LIHU‘E — A new University of Hawai‘i study has discovered that La Nina climate events are growing more common and lasting longer, increasing the likelihood of extreme weather events across the globe.

Bin Wang, atmospheric sciences professor emeritus in UH Manoa’s School of Ocean and Earth Science and Technology, found that five out of six La Nina events since 1998 have lasted longer than one year, including an unprecedented three-year event.

“This is a phenomenon,” Wang said. “In the last 100 years, we only had 10 long La Ninas. But in the last 25 years, we have five. This has caused worldwide concern, whether this long La Nina could occur more frequently in the future.”

Prolonged La Nina periods, lasting between two and three years, can have wide-reaching impacts across the globe, as trade winds along the Pacific Ocean grow stronger than usual and warm water is pushed toward Asia.

In the last 25 years, extended La Ninas have caused severe droughts and heat waves across North America and Eastern Africa, while simultaneously creating record-breaking rainfall and devastating floods in Australia and Western Africa.

“It’s worldwide,” Wang said. “So far, this is the largest source of climate variability all over the world.”

Additionally, Wang and his team found that that when these longer La Ninas subside, they’re often replaced by particularly intense El Nino periods, in which trade winds weaken and warm water is pushed east in the Pacific Ocean.

“Those go hand-in-hand,” Wang said. “It’s not a separate phenomenon.”

That could spell danger for Hawai‘i — El Ninos increase the likelihood of tropical cyclones forming in the western Pacific and moving eastbound toward the state. Both Hurricanes Iniki and Iwa formed during El Ninos.

Recent La Nina periods didn’t just differ from the norm in their longevity, though.

Wang and his team’s study also found that these La Nina formed unique circumstances, owing their durability to varying water temperatures in the Pacific.

Over the last 100 years, the western Pacific Ocean has grown increasingly warmer — largely due to climate change — while the central Pacific has seen significantly less temperature change. This gradient, Wang and his team noted, exacerbates trade winds and fuels the extended events.

“Our perception moves beyond the current notion that links extreme El Nino and La Nina to the eastern Pacific warming, and attributes the increasing extreme El Nino and La Nina to different sources,” Wang said. “The knowledge gained from our study offers emergent constraints to reduce the uncertainties in projecting future changes of extreme La Nina, which may help us better prepare for what lies ahead.”

Further research on what causes exceedingly long three-year La Ninas, as well as evaluations of existing climate models, are needed following the study, Wang said.


Jackson Healy, reporter, can be reached at 808-647-4966 or
Source: The Garden Island

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