When will the sixth mass extinction happen? A Japanese scientist may have an answer

But will still kill more species than before.
Ameya Paleja
Post apocalyptic urban landscape
Post apocalyptic urban landscapeBulgac/iStock
  • Earth's average surface temperature and loss of biodiversity have a linear relation
  • The biggest mass extinction happened 250 million years ago
  • A temperature of 9oC is needed for a mass extinction event

A Japanese climate scientist has run the numbers for the next big mass extinction and does not expect us to reach there till the year 2500 AD, ScienceAlert reported.

The recent round of heatwaves results from climate change that human activity has sped up over the past few centuries. Our home planet goes through cycles of extreme heat to extreme cold and back and forth again. As the cycle progresses from the peak of extreme cold to the extreme heat, there have been times when a large number of species have disappeared in a relatively short period of time. These are called mass extinction events.

In case you aren't aware, the Earth has gone through five such mass extinction events over the past 540 million years. The largest of these events occurred 250 million years ago and claimed 95 percent of the species on the planet. Scientists have been trying to predict when the next one is likely to be due.

The next mass extinction

Previous studies have shown that mass extinction events closely follow those of climate change that have been triggered by asteroids or volcanic activity. When Kunio Kaiho, the Japanese climate scientist, tried to map the stability of the Earth's average surface temperature to that of its biodiversity, he found almost a linear relation between them. When the temperature change is greater, the extent of extinctions is also large.

There was a slight difference, though. Kaiho found that when the Earth cools, the greatest extinctions happen when the temperatures drop by about 7oC. However, when the Earth is warming up, the greatest mass extinctions happen when temperatures have increased by 9oC.

When will the sixth mass extinction happen? A Japanese  scientist may have an answer
Forest fire
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Since the Earth is currently in the global warming phase, by Kaiho's calculations, we would need to warm up significantly more to reach the dreadful benchmark. To put that into perspective, previous studies have suggested that a mere 5.2oC increase in Earth's temperature would bring about a mass extinction event comparable to the previous one that occurred.

Also, warnings by climate scientists have said that at the current rate of emissions, the Earth would warm up by as much as 4.4oC by the end of the century, and current efforts are focused on not letting that happen.

Do we have more time on our hands then?

Kahio predicts that even under the worst-case scenario, the 9oC change in temperatures on the planet is unlikely to happen until 2500 A.D. So, did our safety net just increase? Do we have more time to slow down our emissions?

Kahio does not think so. "Prediction of the future anthropogenic extinction magnitude using only surface temperature is difficult because the causes of the anthropogenic extinction differ from causes of mass extinctions in geologic time," Kahio told ScienceAlert.

What he means is that the accelerated pace that human civilization has brought upon this climate change continues to put species at risk. His calculations show that the extent of the damage may not be massive as in previous events, but the damage is happening faster nevertheless.

The largest mass extinction on record that occurred 250 million years ago took place over a period of 60,000 years. However, what we are facing now is happening much faster in a few centuries. The faster rate of this change may not give species sufficient time to adapt, and even though the warming may not be high, we might end up losing a higher number of species in the next extinction event. For that, humanity alone will be responsible.

Kahio's calculations were published in the journal Biogeosciences.

Abstract

Major mass extinctions in the Phanerozoic Eon occurred during abrupt global climate changes accompanied by environmental destruction driven by large volcanic eruptions and projectile impacts. Relationships between land temperature anomalies and terrestrial animal extinctions, as well as the difference in response between marine and terrestrial animals to abrupt climate changes in the Phanerozoic, have not been quantitatively evaluated. My analyses show that the magnitude of major extinctions in marine invertebrates and that of terrestrial tetrapods correlate well with the coincidental anomaly of global and habitat surface temperatures during biotic crises, respectively, regardless of the difference between warming and cooling (correlation coefficient R=0.92–0.95). The loss of more than 35 % of marine genera and 60 % of marine species corresponding to the so-called “big five” major mass extinctions correlates with a >7 ∘C global cooling and a 7–9 ∘C global warming for marine animals and a >7 ∘C global cooling and a >7 ∘C global warming for terrestrial tetrapods, accompanied by ±1 ∘C error in the temperature anomalies as the global average, although the amount of terrestrial data is small. These relationships indicate that (i) abrupt changes in climate and environment associated with high-energy input by volcanism and impact relate to the magnitude of mass extinctions and (ii) the future anthropogenic extinction magnitude will not reach the major mass extinction magnitude when the extinction magnitude parallelly changes with the global surface temperature anomaly. In the linear relationship, I found lower tolerance in terrestrial tetrapods than in marine animals for the same global warming events and a higher sensitivity of marine animals to the same habitat temperature change than terrestrial animals. These phenomena fit with the ongoing extinctions.

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