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A blob of warm water sits on top of the Pacific Ocean. How it moves along the equator influences weather around the globe, including in the Palmetto State.
Under neutral conditions, trade winds move this warm water along the equator toward Asia. As this warm surface water is pushed westerly, cold water rises from beneath to replace it. Disruptions are common.
During El Niño events, the trade winds become weaker than usual, and the warm water blob floats easterly towards South America. For the Southeast, El Niño cycles are associated with fewer hurricanes in the Atlantic Ocean, more rainfall and higher flood risks.
During La Niña events, trade winds pick up and become stronger than usual, creating unusually cold conditions in the Pacific. For the Southeast, this generally means a more active Atlantic hurricane season with stronger storms and increased risk of drought conditions.
Scientists call this phenomenon the El Niño-Southern Oscillation (ENSO) cycle, and it's ancient. A new study out of Duke University shows that El Niño and La Niña events have been influencing global weather for at least 250 million years -- and with greater intensity in the past. The researchers say understanding these climate patterns' past behavior is key to predicting our climate future.
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"If we want to have a more reliable future projection, we need to understand past climates first," said Shineng Hu, assistant professor of climate dynamics at Duke University.
Hu, Xiang Li (postdoc researcher and lead author on the study) and other contributors used a climate modeling tool usually meant for projecting future climate change to see into the deep past. They ran different models to account for changes in paleogeography, solar radiation levels and carbon dioxide levels.
"At times in the past, the solar radiation reaching Earth was about 2 percent lower than it is today, but the planet-warming CO2 was much more abundant, making the atmosphere and oceans way warmer than present," Hu said.
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The study revealed that El Niño and La Niña predate the world as we know it: In the Mesozoic period, 250 million years ago, the Pacific Ocean didn't exist -- instead the oscillation between El Niño and La Niña occurred in the Panthalassic Ocean to the west of the supercontinent Pangea, Li said.
It also showed that the oscillation between El Niño and La Niña was much stronger in the past than it is now, which Li said was the most important and exciting finding of the study.
The researchers pointed to ocean temperature and wind. More specifically, they found ocean temperature fluctuations at different depths and "atmospheric noise" of ocean surface winds were the two most important variables in understanding why the strength of these climate patterns have changed.
In the deep past, oceans were hotter, temperatures swings were bigger and levels of "noise" in the atmosphere from winds varied. More "noise" in the atmosphere signaled more unpredictable (though not necessarily more extreme) weather, Li said.
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Past studies have focused solely on ocean temperatures, but Li and Hu's simulations show the importance of atmospheric noise and trade winds, which play a critical role in activating El Niño and La Niña events. Paying attention to both temperature and wind could make climate projections more reliable, Li said.