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More evidence suggests Earth is entering a sixth extinction-level event

A new paper from Stanford, Princeton, and Berkeley suggests that the world has begun a sixth extinction-level event, this one driven primarily by humankind. This new research indicates that the fossil record clearly shows that species of every sort are becoming extinct far more rapidly than the historical background rate would suggest, and that much of the change is driven by humanity, including the impact of climate change.

The previous extinction events. Percentage to the left is total number of species’ killed. Image courtesy of Wikipedia

The report set out to answer whether current extinction rates for mammals and vertebrates were higher than the highest background level observable through the fossil record, how extinction rates have changed over time within observed history, and how many years it would take species to go extinct if the background extinction rate had held steady. The so-called “background rate” of extinction is extremely important. It’s the number of species that we can predict would have gone extinct, even without outside intervention.

While the point of the paper was to measure the impact of humans, thousands of species of plants, animals, reptiles, amphibians, and birds have historically gone extinct without any human intervention whatsoever, while others (the dodo bird, Steller’s sea cow, the passenger pigeon, and the Rodriguez giant tortoise) were killed off by humans long before climate change was a concern. A high background extinction rate will make any modern departure from the norm less serious-looking, while a low background extinction rate emphasizes the modern departure from historical norms.

In the past, scientists have estimated that species tend to go extinct at a rate between 0.1 and 1 species per million species per year, but for the purposes of this paper, the team of researchers decided on a background extinction rate of 2E/MSY (meaning two species for every million species, every million years). Because we can’t be certain of accounting for every single species, including species that do not decay and leave fossilized materials, there’s always going to be some slippage in the figures — but we can still chart the extinction rate of well-represented species and compare against historical records when that data is available.

ExtinctionEvent1-640x277This chart shows the number of extinct creatures since 1500 and 1900 for each available species classification. The Highly Conservative rates include only species no longer believed to exist at all, anywhere on Earth. While it’s true that some of these species are later rediscovered, the rate of rediscovery is extremely low and typically confined to tiny, endangered populations located in an heretofore-unknown spot. The Conservative table includes those species believed to be extinct in the wild or possibly extinct. In both cases, the extinction rates shot up after 1900, once the industrial revolution and modern record keeping where both underway.




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