Duke University researchers and collaborating scientists took a peek into the last 250 million years to understand the causes of massive temperature oscillation events El Niño and La Niña.
By Lily Roby, Courthouse News Service
As recent conditions in the Pacific Ocean favor the development of a La Niña event later this year, researchers have discovered that this cycle of temperature swings was likely occurring at least 250 million years ago, and on an even greater scale.
A modeling study published Monday in Proceedings of the National Academy of Sciences shows that El Niño and its cold counterpart, La Niña, were intensely experienced by the dinosaurs of the Mesozoic era.
Utilizing the modeling tool that is used by the Intergovernmental Panel of Climate Change to predict future climate change, Duke researchers and collaborating scientists instead looked into the past, breaking down the 250 million years into 26 10-million-year ‘slices’ to analyze.
“In each experiment, we see active El Niño Southern Oscillation,” Shineng Hu, assistant professor of climate dynamics at Duke University’s Nicholas School of the Environment, said in a press release. “It’s almost all stronger than what we have now. Some way stronger, some slightly stronger.”
An El Niño is declared by meteorologists at organizations like the National Oceanic and Atmospheric Administration when the average temperature of a patch of the Pacific Ocean maintains a temperature at least 0.5 degrees Celsius or 32.9 degrees Fahrenheit above average for five consecutive months. The climate event alters the jet stream, causing drastic climate changes — like an unusually dry northwest and an excessively rainy southwest in the United States.
Its cooling twin La Niña does the opposite. Large patches of cold ocean water push the jet stream north, causing east African droughts and harsh monsoons in south Asia.
According to NOAA, these weather events last nine to twelve months and seem to occur every two to seven years, with El Niño being more common. However, that knowledge is based on data collected in recent history.
“If we want to have a more reliable future projection, we need to understand past climates first,” Hu said.
During the Mesozoic period, when dinosaurs ruled the supercontinent Pangea, El Niño and La Niña events happened with much more frequency, with annual mean surface temperatures hitting a high of 77.9 degrees Fahrenheit and Arctic temperatures reaching a sweltering 50 degrees Fahrenheit. This temperature is about 59 degrees higher than the average temperatures in the pre-industrial period, or the time period just before human society began to affect global temperatures with industrialization.
After Pangea broke up during the Jurassic period, about 200 million years ago, researchers found that global temperatures were still excessively high, trade winds persisted over the tropical Pacific ocean, and cool waters could be found in the eastern Pacific ocean by the equator. All of these conditions are more drastic examples of side effects of the modern weather events known as El Niño and La Niña.
But making these discoveries wasn’t a breeze. It took months of effort from scientists as they simulated thousands of years in the model.
Factors like solar radiation, ocean surface winds, planet-warming carbon dioxide and the consideration of the location of land and water as Pangea broke apart were essential in ensuring the weather prediction model was accurate. During the era of Pangea, oscillating temperatures occurred in the western Panthalassic Ocean, as the modern Pacific Ocean didn’t yet exist.
“Atmospheric noise — the winds — can act just like a random kick to this pendulum,” Hu said, comparing this warming and cooling of global temperatures to a swaying pendulum. “We found both factors to be important when we want to understand why the El Niño was way stronger than what we have now.”
In earlier, similar studies aiming to understand these weather events, researchers spent most of their time tracking past ocean temperatures. However, to make this innovative revelation, Hu and his colleagues focused on both the thermal structure of the ocean and the ‘atmospheric noise’ of wind over the past 250 million years.
“So part of the point of our study is that, besides ocean thermal structure, we need to pay attention to atmospheric noise as well and to understand how those winds are going to change,” Hu said.