A recent modeling study indicates that the El NiƱo phenomenon, characterized by a significant mass of warm water in the tropical Pacific Ocean capable of altering global rainfall patterns, is not solely a contemporary event.
The El NiƱo phenomenon, a significant area of warm ocean water in the tropical Pacific capable of influencing rainfall worldwide, has roots dating back far beyond modern times.
A study conducted by researchers from Duke University, in collaboration with others, has revealed that the variations between El NiƱo and its chilly counterpart, La NiƱa, were present at least 250 million years ago and were sometimes more intense than the fluctuations observed today.
According to the research appearing the week of Oct. 21 in the Proceedings of the National Academy of Sciences, these temperature variations were stronger in the past, occurring even when the continents were arranged differently than they are today.
Shineng Hu, assistant professor of climate dynamics at Duke University’s Nicholas School of the Environment, stated, “In each experiment, we observe an active El NiƱo Southern Oscillation, and many are stronger than what we experience nowāsome significantly stronger and others just slightly so.”
Climate scientists closely study El NiƱo, a large area of warmer water flanking the equator in the eastern Pacific, due to its ability to modify the jet stream. This can lead to dryer conditions in the northwestern U.S. while causing excessive rainfall in the southwestern region. In contrast, La NiƱa, with its cooler temperatures, can drive the jet stream northward, leading to dry spells in the southwestern U.S. while also contributing to droughts in East Africa and intensifying the monsoon season in South Asia.
The research team employed the same climate modeling tools used by the Intergovernmental Panel on Climate Change (IPCC) to predict future climate scenarios but ran them in reverse to explore ancient climatic conditions.
Due to the computation-heavy nature of simulations, researchers couldn’t analyze each year continuously from 250 million years ago; instead, they examined 10-million-year intervalsātotaling 26 slices.
“The model tests were affected by various boundary conditions, including different land-sea distributions, altered solar radiation levels, and variations in CO2 concentrations,” explained Hu. Each simulation ran for thousands of model years to ensure accuracy and took several months to complete.
“Historically, the solar radiation reaching Earth was approximately 2% lower than today, yet the levels of CO2 were significantly higher, which contributed to much warmer oceans and atmosphere,” Hu elaborated. During the Mesozoic era, around 250 million years ago, South America occupied the central area of the supercontinent Pangea, and the oscillation occurred in the adjacent Panthalassic Ocean.
The study signifies that the two primary factors influencing the intensity of the oscillation over time appear to be the warmth distribution within the ocean and the ‘atmospheric noise’ generated by ocean surface winds.
Whereas prior research has concentrated largely on ocean temperatures, this study emphasizes the significance of surface winds, which are equally critical, according to Hu. “One main takeaway from our study is that we must examine both the ocean’s thermal structure and the atmospheric noise to grasp how wind patterns might evolve,” he commented.
Hu compares the oscillation to a pendulum, stating, “Atmospheric noiseāthe windsācan serve as random pushes to this pendulum. Our findings indicate that both elements are vital for comprehending why the past El NiƱo events were significantly stronger than what we currently observe.”
Hu concluded, “To achieve more reliable future predictions, it’s essential first to understand historical climates.”
This research received support from the National Natural Science Foundation of China (42488201) and the Swedish Research Council VetenskapsrƄdet (2022-03617). Simulations took place at the High-performance Computing Platform at Peking University.
