About 252 million years ago, the Earth nearly perished. In the oceans, 96% of all species died. It is more difficult to determine how many terrestrial species have disappeared, but the losses were similar. This mass extinction at the end of the Permian period was the largest in the entire history of the planet and lasted for several thousand years.
A team of experts prepared a detailed report on how marine life was obliterated during the Permian-Triassic mass extinction. Global warming has robbed the oceans of oxygen, stressing many species to the point that they die.
And we can repeat this process, scientists warn. If so, climate change "is clearly categorized as catastrophic extinction," says Curtis Deutsch of the University of Washington, co-author of the new study.
Researchers have long known the general concepts of the Permian-Triassic cataclysm. Volcanoes on the territory of modern Siberia began to erupt with great force. The lava they emitted produced a huge amount of carbon dioxide.
Once in the atmosphere, the gas began to capture heat. Researchers estimate that the ocean surface has warmed by 18 degrees Fahrenheit. Some scientists say that it was the heat that killed many species.
Others believe that the heat reduced the oxygen concentration in the ocean, suffocating the species that lived there. The mass extinction rock was formed when at least part of the ocean was lacking oxygen.
In his previous study, Deutsch examined how modern animals adapted to the temperature and oxygen levels of the seas. Animals with fast metabolism needed more oxygen, and therefore they could not live in those parts of the ocean where oxygen levels were below a certain threshold.
Warm water made the test more difficult because it cannot hold as much dissolved oxygen as cold water. To make matters worse, warm water can increase the metabolism of animals, meaning that they need more oxygen to survive.
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Deutsch and his colleague Justin Penn recreated the world of the late Permian using large-scale computer simulations. When Siberian volcanoes flooded the virtual atmosphere with carbon dioxide, the atmosphere warmed. The ocean also warmed and, according to the model, began to lose oxygen.
Some parts of the ocean lost more oxygen than others. On the surface, for example, fresh oxygen was produced by photosynthetic algae. But as the ocean warmed, its circulating currents also slowed down, the model showed. The oxygen-poor water settled to the bottom of the oceans, and soon the depths began to choke.
Rising temperatures and falling oxygen levels have left vast swaths of oceans uninhabited. Some species survived, but most disappeared completely. Animals in oxygen-rich waters were unable to tolerate the sudden drop in oxygen, and those that lived in tropical waters were already adapted to low O2 levels. Cold-water species could find no refuge anywhere.
The new study carries an important warning. Siberian volcanoes eventually emitted as much carbon dioxide into the atmosphere as we would never produce by burning fossil fuels. But our annual rate of carbon dioxide emissions is actually higher.
The carbon dioxide we've emitted over the past two centuries has already warmed the atmosphere, and the ocean has absorbed most of that heat. And now, just like during the Permian-Triassic extinction, the ocean is losing oxygen. Over the past 50 years, oxygen levels have dropped by 2%. If we use all of the fossil fuels on Earth, the planet could warm by 17 degrees Fahrenheit by 2300.