Modeling experiments show that the climate-changing El Niño oscillation is at least 250 million years old.

The El Niño event, a massive mass of warm ocean water in the tropical Pacific Ocean that can change precipitation patterns around the world, is not just a modern phenomenon.

A new modeling study by two Duke University researchers and their colleagues shows that the oscillation between El Niño and its cold counterpart, La Niña, was present at least 250 million years ago and was often a magnitude greater than the oscillations we know. see today.

These temperature variations were more intense in the past, and the oscillation occurred even when the continents were in different locations than they are today, according to the study appearing October 21 in the journal. Proceedings of the National Academy of Sciences.

“In every experiment, we observe an active El Niño Southern Oscillation, and it is almost entirely stronger than what we have now, some much stronger, some slightly stronger,” said Shineng Hu, assistant professor in climate dynamics at the Nicholas School of the at Duke University. Environment.

Climatologists study El Niño, a giant patch of unusually warm water on either side of the equator in the eastern Pacific Ocean, because it can change the jet stream, drying out the northwest United States while flooding the southwest with unusual rains. Its counterpart, the cold blob La Niña, can push the jet stream northward, drying out the southwest United States, while causing drought in East Africa and making the monsoon season more intense in South Asia.

The researchers used the same climate modeling tool used by the Intergovernmental Panel on Climate Change (IPCC) to try to project climate change into the future, except they ran it backwards to see the deep past.

The simulation is so computationally intense that researchers have not been able to model every year continuously for 250 million years. Instead, they made “slices” of 10 million years, or 26 of them.

“The model experiments were influenced by different boundary conditions, such as different land-sea distribution (with the continents in different locations), different solar radiation, different CO₂“, said Hu. Each simulation lasted thousands of model years to obtain robust results and took months.

“In the past, solar radiation reaching Earth was about 2% lower than it is today, but planet-warming CO2₂ “During the Mesozoic period, 250 million years ago, South America was the middle part of the supercontinent Pangea, and the wobble occurred across the Panthalassic Ocean to its present tip. West.

The study shows that the two most important variables in the magnitude of the oscillation appear historically to be the thermal structure of the ocean and the “atmospheric noise” of winds at the ocean surface.

Previous studies have focused primarily on ocean temperatures, but paid less attention to the surface winds that appear so important in this study, Hu said. “So part of the point of our study is that in addition to the thermal structure of the oceans, we also need to pay attention to atmospheric noise and understand how these winds will change.”

Hu compares the oscillation to a pendulum. “Atmospheric noise – winds – can act as a random kick on this pendulum,” Hu said. “We found that these two factors are important when we want to understand why the El Niño phenomenon was much stronger than what we currently experience.”

“If we want to have a more reliable future projection, we must first understand past climates,” Hu said.