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Biologists assessed the overall biological habitat by counting and categorizing biodiversity of the Little Corona del Mar tide pools, part of the Crystal Cove State Marine Conservation Area Wednesday, Oct. 6, 2021 in Newport Beach, California.

As an oil spill spread across Orange County, a team of biologists from the University of California Santa Cruz and Tenera Consulting firm assessed the overall biological habitat by counting and categorizing biodiversity of the Little Corona del Mar tide pools, part of the Crystal Cove State Marine Conservation Area Wednesday, Oct. 6, 2021 in Newport Beach, California. (Photo: Allen J. Schaben / Los Angeles Times via Getty Images)

Scientists Decry Human Indifference to 'Probable Sixth Mass Extinction'

"Denying the crisis, accepting it without reacting, or even encouraging it constitutes an abrogation of humanity's common responsibility," said one scientist behind the new study.

Andrea Germanos

There's a human-caused extinction crisis underway—probably the start of the Sixth Mass Extinction—and denial or indifference to this planetary crisis is "an abrogation of moral responsibility," according to scientists behind a new study.

"We cannot help but feel that humanity is allowing a probable Sixth Mass Extinction to unfold."

Published last week in the journal Biological Reviews, the assessment by biologists from the University of Hawai'i at Mānoa and the Muséum National d’Histoire Naturelle in Paris finds that the unprecedented rate of species loss is undeniable. The authors reject both the argument that the human-caused loss of species are simply a natural trajectory of life on Earth and that extinction rates are exaggerated.

Part of the issue, they say, may rest in a reliance on the "Red List" maintained by the International Union for Conservation of Nature (IUCN). The list, despite assessing over 120,000 species, covers a mere 5.6% of the over 2.2 million animal and plant species recognized by taxonomists.

In addition to likely underestimating extinctions of those listed, the authors say the compilation is also heavily skewed toward non-marine vertebrates while invertebrates—both on land and in the sea—constitute up to 97% of known animal species.

"Including invertebrates was key to confirming that we are indeed witnessing the onset of the Sixth Mass Extinction in Earth's history," said lead author Robert Cowie, a research professor at the UH Mānoa Pacific Biosciences Research Center in the School of Ocean and Earth Science and Technology.

The researchers point to data on molluscs, which are the second-largest phylum of invertebrates and whose long-lasting shells leave an important historical record. They extrapolate mollusc extinction rates to assess greater biodiversity losses, though noting that data shows marine and plant species have fared better in the extinction crisis than land animals.

Their findings show there are 638 mollusc species extinct and 380 possibly extinct—figures that add up to more than twice as many listed by IUCN's 2020 assessment.

Making a "bold" extrapolation on data on 200 land snail species, the study finds that 7.5% to 13% of roughly 2 million species have gone extinct in the last 600 years. That's between 150,000 and 260,000 species in total.

It's clear there is a crisis is underway, the researchers say.

"The Sixth Mass Extinction may have not occurred yet, but heightened rates of extinction and huge range and population declines have already occurred, and whatever it is called, biodiversity is changing at a greater rate than it would in the absence of anthropogenic influences," they wrote.

"This is a fact," the researchers continued. "Denying it is simply flying in the face of the mountain of data that is rapidly accumulating, and there is no longer room for scepticism, wondering whether it really is happening."

The scientists reject the argument that humans are simply "just another species going about its business in the greater evolutionary scheme of things, an argument that gives carte blanche to those who would destroy the Earth for their own short-term gain." Humankind has a "power to manipulate the Earth on a grand scale," they add, and has "a moral and ethical obligation to use that power judiciously not capriciously."

"We cannot help but feel that humanity is allowing a probable Sixth Mass Extinction to unfold," the authors lament, "and it is pie in the sky to think that this situation will change in any major way."

Still, important efforts to at least slow down the crisis are underway, the study notes, pointing to mobilizations by groups of individuals like Extinction Rebellion and the establishment of protected areas as examples.

Yet more must be done, the researchers say, including by biological scientists who should "spread the message that the biodiversity that makes our world so fascinating and beautiful is going extinct unnoticed at an unprecedented rate" and should also collect species and their descriptions before they go exinct.

According to Cowie, "Despite the rhetoric about the gravity of the crisis, and although remedial solutions exist and are brought to the attention of decision-makers, it is clear that political will is lacking."

“Denying the crisis, accepting it without reacting, or even encouraging it," said Cowie, "constitutes an abrogation of humanity's common responsibility and paves the way for Earth to continue on its sad trajectory towards the Sixth Mass Extinction."

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