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Gaworecki writes: "New research by scientists at the United States' University of Washington and Stanford University suggests that the most destructive mass extinction event in Earth's ancient history was caused by global warming that left marine life unable to breathe."

Great Barrier Reef. (photo: National Geographic)
Great Barrier Reef. (photo: National Geographic)

Worst Mass Extinction Event in Earth's History Was Caused by Global Warming Analogous to Current Climate Crisis

By Mike Gaworecki, Mongabay

04 January 19


ew research by scientists at the United States’ University of Washington and Stanford University suggests that the most destructive mass extinction event in Earth’s ancient history was caused by global warming that left marine life unable to breathe.

The Permian period, the last period of the Paleozoic Era, ended about 250 million years ago with the largest recorded mass extinction in Earth’s history. Before the dinosaurs emerged during the Triassic period somewhere around 243 and 233 million years ago, a series of massive volcanic eruptions is believed to have triggered global climate change that ultimately led to the Permian extinction, which wiped out 96 percent of marine species in an event known as the “Great Dying.”

According to Justin Penn, a doctoral student at the University of Washington (UW), the Permian extinction can help us understand the impacts of climate change in our own current era. He’s the lead author of a study published in Science last month that builds off of previous research by Curtis Deutsch, a professor of oceanography at UW.

“In 2015, Curtis published a paper demonstrating that temperature and oxygen act as invisible barriers to habitat for animals in the modern ocean,” Penn told Mongabay. “We wanted to know whether this framework could be used to understand the link between ocean warming, oxygen loss, and marine ecosystems. The end-Permian mass extinction served as the perfect case study because there is clear evidence for ocean warming and oxygen loss during that time period, and the fossils recorded the response of marine biodiversity.”

Penn led a team of researchers that combined models of ocean conditions and animal metabolism with paleoceanographic records to show that the Permian mass extinction was caused by rising ocean temperatures, which in turn forced the metabolism of marine animals to speed up. Increased metabolism meant increased need for oxygen, but the warmer waters could not hold enough oxygen to meet those needs, and ocean life was left gasping for breath.

During the Permian period, Earth’s land masses were still joined together in the supercontinent of Pangaea, and before volcanic eruptions in Siberia increased the concentrations of greenhouse-gas’s in the atmosphere, ocean temperatures and oxygen levels were similar to those of today. The researchers constructed a model based on Earth’s configuration and climate in the Permian, then raised greenhouse gases in the model until ocean surface temperatures in the tropics had risen by 10 degrees Celsius (20 degrees Fahrenheit), the conditions driven by the global warming that was occurring at the time.

The global warming and oxygen loss simulated in the Earth System model Penn and team built matched reconstructions of these changes made from the fossil record of the end of the Permian period. The oceans lost about 80 percent of their oxygen, and around half of the ocean seafloor became completely oxygen-free, especially at lower depths.

The researchers then used published lab measurements on 61 modern marine species like crustaceans, fish, shellfish, corals, and sharks to examine how those animals might respond to those oxygen and temperature conditions. Today’s marine wildlife are expected to have similar tolerances to high temperatures and low oxygen as Permian animals because of the similar environmental conditions under which they evolved.

“Warming and oxygen loss would have led to a loss of aerobic habitat for marine animals by increasing their temperature-dependent oxygen demand amid declining supply,” Penn said. “The predicted geography and severity of the resulting mass extinction explain the patterns observed in the global marine fossil record from the ‘Great Dying.’”

In a statement, Curtis Deutsch explained that by combining species’ traits with the team’s paleoclimate simulations, the researchers were able to predict the geography of the extinction event. “Very few marine organisms stayed in the same habitats they were living in — it was either flee or perish,” Deutsch, a co-author of the Science paper, said.

The model predicted that, because animals found at high latitudes far from the tropics are the most sensitive to oxygen levels, their numbers would have suffered the most, with those that have particularly high oxygen demands being almost completely wiped out. Many tropical species would have gone extinct, as well, the model showed.

“Since tropical organisms’ metabolisms were already adapted to fairly warm, lower-oxygen conditions, they could move away from the tropics and find the same conditions somewhere else,” Deutsch said. “But if an organism was adapted for a cold, oxygen-rich environment, then those conditions ceased to exist in the shallow oceans.”

To test the predictions made by the climate model, study co-authors Jonathan Payne and Erik Sperling of Stanford University turned to the Paleobiology Database, a virtual archive of published fossil collections. By looking at how fossils are distributed in ancient seafloor rocks, it’s possible to piece together where animals existed before the extinction event, where they they fled to or went extinct, or where they were confined to a fraction of their previous habitat. The fossil distributions of the late-Permian period confirmed that species far from the equator were hit the hardest by the mass extinction event.

“The signature of that kill mechanism, climate warming and oxygen loss, is this geographic pattern that’s predicted by the model and then discovered in the fossils,” Penn said in a statement. “The agreement between the two indicates this mechanism of climate warming and oxygen loss was a primary cause of the extinction.”

Penn and co-authors say that other shifts in the ocean environment, such as acidification or changes in the productivity of photosynthetic organisms, probably contributed to the Permian extinction, but that warmer temperatures leading to insufficient oxygen levels accounts for more than half of the losses in marine life.

That could help us understand how marine life will fare in our current age of global warming, Penn added, because the conditions in the late Permian are similar to conditions today.

The drivers of the Permian mass extinction — volcanic CO2 emissions into the atmosphere leading to global warming — are analogous to human-caused CO2 emissions occurring today, Penn noted. “These results allow us to compare the scale of our modern problem to the largest extinction in Earth’s history,” he told Mongabay. “Under a business-as-usual emissions scenarios, by 2100 warming in the upper ocean will have approached 20 percent of warming in the late Permian, and by the year 2300 it will reach between 35 and 50 percent.”

The study, therefore, highlights the potential for a mass extinction driven by anthropogenic climate change due to mechanisms similar to those that caused the Permian mass extinction, Penn said: “The ocean cannot be cooled or oxygenated on a global scale by any feasible means. The only sustainable solution to reduce the risk of temperature-dependent hypoxia is to halt the anthropogenic accumulation of CO2 in the atmosphere.”

This article was originally published on Mongabay.

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