A climate scientist at Tohoku University in Japan has run the numbers and doesn’t think today’s mass extinction will match that of the previous five. At least not for many centuries to come.
In more than one instance over the past 540 million years, Earth has lost most of its species in a relatively short geological time span.
These are known as mass extinction events and often closely follow climate change, whether from extreme warming or extreme cooling caused by asteroids or volcanic activity.
When Kunio Kaiho tried to quantify the stability of Earth’s average surface temperature and the planet’s biodiversity, he found a largely linear effect. The greater the temperature change, the greater the extinction rate.
For global cooling events, the largest mass extinction occurred when temperatures fell by about 7°C. But for global warming events, Kaiho found that the largest mass extinctions occurred at warming of about 9°C.
This is much higher than previous estimates, which suggested that a temperature of 5.2°C would lead to a major mass marine die-off, on par with the previous Big Five.
To put it in perspective, by the end of the century, modern global warming is on track to raise surface temperatures by as much as 4.4°C.
“Global warming of 9°C will not occur during the Anthropocene until at least 2500 in the worst-case scenario,” Caiho predicted.
Kaiho does not deny that many extinctions on land and in the sea are already occurring due to climate change; he just doesn’t expect the same loss ratio as before.
Yet it’s not just the extent of climate change that puts species at risk. The speed at which it happens is vitally important.
The largest mass extinction event on Earth wiped out 95 percent of known species at the time and occurred more than 60,000 years ago, about 250 million years ago. But today’s warming is happening on a much shorter timescale thanks to human emissions of fossil fuels.
Perhaps more species will die out in Earth’s sixth mass extinction not because the rate of warming has been so great, but because the changes have occurred so rapidly that many species have been unable to adapt.
“Predicting the future magnitude of anthropogenic extinction using surface temperature alone is difficult because the causes of anthropogenic extinction differ from the causes of mass extinctions in geologic time,” Kaihu admits.
Regardless of how scientists compile the data, it’s clear that many species are doomed unless we can stop climate change.
The exact rate of losses and the timing of those losses remain up for debate.
The research is published in Biogeosciences.
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