By A barrage of intense, wild swings in climate conditions may have fueled the largest mass extinction in Earth’s history. A re-creation of how ancient sea surface temperatures, ocean and atmosphere circulation, and landmasses interacted revealed an Earth plagued by nearly decade-long stints of droughts, wildfires and flooding.
Researchers knew that a spike in global temperatures — triggered by gas emissions from millions of years of enormous volcanic eruptions in what is now Siberia — was the likely culprit behind a mass extinction roughly 252 million years ago (SN: 8/28/15). But it was the resulting catastrophic “mega El Niños” that whiplashed ecosystems, ultimately wiping out some 90 percent of all ocean species and 75 percent of those on land, researchers report in the Sept. 13 Science.
“[The findings] really build into an emerging picture that it’s a bit more nuanced of an extinction than we previously had appreciated,” says Erik Gulbranson, a sedimentary geochemist at Gustavus Adolphus College in Saint Peter, Minn., who was not involved with the new study.
Researchers have wondered why the Great Dying that played out at the border of the Permian and Triassic periods was so brutal for life on Earth. “We’ve got this intense global warming, but we have other episodes of global warming in the geological record that don’t do anything nearly as bad to ecosystems as this,” says paleontologist David Bond at the University of Hull in England.
While a sharp increase in sea surface temperature plus the resulting collapse in the warmer ocean’s ability to hold dissolved oxygen would have been abysmal for ocean organisms, it wasn’t clear what drove the extinction of life on land or why these organisms couldn’t just move to the cooler poles.
Part of the answer may lie in much shorter-term oscillations in paleoclimate.
“Species care about climate, but what they also really care about is weather,” says Alexander Farnsworth, a paleoclimate modeler at the University of Bristol in England. Such variations include climate wobbles on the scale of years rather than hundreds of millennia or more. For instance, today’s El Niño-Southern Oscillation — a periodic warming of the tropical Pacific Ocean that brings heat and aridity to northern North America, dampens the Atlantic hurricane season, and induces droughts and floods globally — lasts roughly a year (SN: 2/13/23).
Farnsworth, Bond and an international team of colleagues reconstructed what these climate patterns looked like more than 250 million years ago. The team calculated seawater temperatures using ratios of different forms of oxygen in the fossilized teeth of conodonts, ancient fishlike animals. With this data plus newly updated computer simulations of Earth’s atmospheric and ocean circulation patterns, the team produced a more cohesive picture of climate during the Great Dying. This was aided, says Farnsworth, by a newer, more precise understanding of what continents and ocean basins looked like at the end of the Permian, which influences global atmospheric and ocean circulation.
When carbon dioxide levels initially doubled from about 410 to 860 parts per million and global temperatures rose, the El Niño–like warming spells originating mostly over the late Permian’s giant ocean, Panthalassia, grew more intense, the team found. (In comparison, current CO₂ levels are hovering around 422 ppm.) Over time, the swings lengthened too, sometimes stretching for nearly a decade.
The effects of these mega El Niños would have quickly been too much for land organisms to bear. As carbon dioxide–gobbling forests baked and died back, fewer greenhouse gases were pulled out of the atmosphere, says Farnsworth, creating a self-perpetuating cycle as volcanoes continued to pump out the warming gases.
“You get more warming, more vegetation die-off, stronger El Niños, higher temperatures globally, higher weather extremes again, leading to more die-off,” says Farnsworth. Large swaths of the globe would have lurched from broiling heat, drought and fire to dramatic flooding.
The heat eventually invaded higher latitudes, leaving few places to escape an increasingly hostile atmosphere.
“It became very hot everywhere, and that’s why [species] couldn’t simply migrate north and south,” Bond says.
In the end, many species simply couldn’t adapt to this climate roller coaster.
Now that the findings paint a higher-resolution picture of just how warming precipitated a mass extinction at the end of the Permian, there may be a way to see these rapid climate fluctuations in the fossil record itself. Gulbranson points out that annual records preserved in fossil cave stalactites and tree rings might show evidence of the mega El Niños.
“We need to track down these signals in the fossil record. We need to see them in the organisms that lived and went through the extinction,” he says.
Going forward, Bond is curious about what innate physical and ecosystem features made certain periods in Earth’s history more resilient to calamity from climate chaos, and others more vulnerable to mass extinction.
