Every few years, the El Niño–Southern Oscillation (ENSO), a seasonal climate phenomenon, disrupts global weather for periods of 9–12 months at a time. During an ENSO event, trade winds die down, allowing warmer water to circulate through the Pacific Ocean and creating unpredictable, extreme weather patterns around the world. While some locations experience heavy rainfall, others experience extreme drought and heat waves.
The 2023–2024 ENSO event, one of the strongest on record, contributed to atmospheric rivers and a reduced snowpack, as well as increased instances of wildfire and drought along the U.S. West Coast. Marine temperatures 2℃ warmer than usual affected fish populations and coral reefs and contributed to harmful algal blooms. The World Meteorological Organization reported that 2023 was the hottest year on record, a title that can be connected to the chaotic effects of ENSO.
But even though the changes wrought by an ENSO event may bring dangerous or disruptive weather and temperature extremes, there is some solace in that it’s a temporary state. Events happen between every 2 and 7 years and usually last no more than a year at a time.
About 252 million years ago, however, El Niño–like conditions may have persisted for decades at a time, a new study suggests.
The volatile climate and extended ocean warming associated with this climate pattern may be pieces of the puzzle of what caused the largest mass extinction in Earth’s history, the Permian-Triassic extinction event, also known as the “Great Dying.” During this period, it would have been impossible for plants and animals to endure decades-long swings in climate conditions. Most life on land and sea was wiped out within tens of thousands of years.
Permian Murder Mystery
Up until its dramatic conclusion, the Permian period was “quite a happy place for lots of species. There were lots of big forests. Most species were very happily going along for millions of years at this point, evolving in their own unique ways,” said Alexander Farnsworth, a paleoclimatologist from the University of Bristol and one of the study’s authors.
Then, something—or a series of somethings—happened.
“To reach the exceptionally high extinction rates at the end-Permian was not easy; different kill mechanisms are required to impact both marine and terrestrial life,” said Steve Grasby, a geochemist with the Geological Survey of Canada who was not involved in the new research.
One prevailing theory about the Great Dying’s instigating event considers the climate impacts of the eruption of the prolific network of volcanoes that formed the Siberian Traps. The eruptions took place over millions of years, covering the region in lava, producing acid rain, destroying the ozone layer, and spewing toxic metals—as well as belching out carbon dioxide (CO2) that contributed to extreme global warming.
“It’s like Murder on the Orient Express. As detectives, we had to figure out the conspiracy that generated this environmental disaster.”
But massive volcanoes had erupted, and Earth had warmed before, all without triggering casualties on the scale of the Great Dying. Pangaea was already vulnerable to hostile temperatures and rainfall during the Permian. It didn’t make sense to researchers why species on land, including normally hardy insects, couldn’t migrate to cooler climates and instead died off. The fact that they died off tens of thousands of years before most marine life went extinct only deepens the mystery.
“It’s generally accepted that the extinction on land happens much earlier than in the ocean. This generates a problem. What can kill life on land first?” asked Yadong Sun, one of the study’s authors and a paleoclimatologist at China University of Geosciences in Wuhan. “It’s like Murder on the Orient Express. As detectives, we had to figure out the conspiracy that generated this environmental disaster.”
Tiny Teeth Provide Links to a Larger Catastrophe
One clue to the sequence of catastrophic events came from the fossilized teeth of a prehistoric eellike creature, the conodont.
By analyzing the ratio of oxygen isotopes present in the fossilized teeth, researchers gathered crucial information about prehistoric sea surface temperatures across several locations along the paleoequator. The data revealed reduced temperature gradients in Earth’s giant prehistoric ocean, Panthalassa. In other words, the difference in temperature between the warm, tropical ocean and the cooler, midlatitude ocean began to equalize.
By creating climate models of Pangaea and Panthalassa and re-creating conditions from 252 million years ago, researchers made a surprising connection: “It’s very similar to what we would see in a sort of El Niño,” said Farnsworth.
Warming and cooling conditions similar to our El Niño and La Niña events became amplified by the proliferation of volcanic eruptions and the resulting CO2 in the atmosphere. Panthalassa in particular held heat well because of its size.
Instead of lasting a year, the effects of these ENSO-like events lasted for decades. Droughts scorched tropical forests first, and charcoal found in rocks suggests widespread wildfires. Hot, dry conditions lasted so long that vegetation wasn’t able to recover or act as a carbon sink.
The heat—an increase of 4℃—would eventually progress to higher latitudes, causing terrestrial species to perish first because they couldn’t adapt quickly enough to the wild weather extremes.
“These processes would feed back on one another and lead to real runaway warming, first on land. Then, CO2 built up enough in the atmosphere to warm up the ocean sufficiently, which would then lead to deoxygenation and stratification of the ocean,” said Farnsworth.
After nearly 90% of species were gone, it would take several million years for complex ecosystems to return.
El Niños Past, Present, and Future
“The study is exciting, as it combined geochemical proxy data, sedimentological evidence, and state-of-the-art Earth system climate modeling to show that the Earth was highly susceptible to prolonged and intensified El Niños,” said Grasby. “These short-term climate variabilities, which are common today, could lead to catastrophic consequences in a warming background.”
Elements of environmental deterioration in the end-Permian period parallel our current climate reality. For instance, models suggest that prehistoric Earth reached its tipping point when the partial pressure of carbon dioxide in Earth’s atmosphere jumped from about 410 parts per million (ppm) to 800 ppm. “We are at 440 ppm today,” said Sun. “If we were in the Permian-Triassic time, we are heading [to the Great Dying]. We are not yet there. We can still do something.”
Even if the ENSO cycle changes wildly, we won’t experience conditions nearly as brutal as those at the end of the Permian.
Some models suggest ENSO events becoming more variable by 2100, Farnsworth noted. Whether this means they’ll be longer, stronger, or some combination of the two is uncertain. The consequences of these changes are unknown, as the effects of even a normal El Niño can cause damage to ecosystems already stressed by a changing climate.
The good news is that the configuration of our continents means that even if the ENSO cycle changes wildly, we won’t experience conditions nearly as brutal as those at the end of the Permian.
“The modern ocean is a much better buffer than before,” said Sun. “We have much more complex ecosystems.”
—Rebecca Owen (@beccapox), Science Writer
