A climate scientist at Tohoku University in Japan has crunched the numbers and doesn’t think today’s mass extinction is on par with the previous five. At least not for many more centuries.
On more than one occasion during the past 540 million years, Earth has lost most of its species in a relatively short geologic time span.
These are known as mass extinction events, and often closely follow climate change, either due to 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.
For global cooling events, the largest mass extinctions occurred when temperatures dropped by about 7°C. But for global warming events, Kaiho found that the largest mass extinctions occurred with warming of about 9°C.
This is much higher than previous estimates, which suggested that a temperature of 5.2°C would result in a major marine mass extinction, on par with the previous “big five”.
To put this in perspective, by the end of the century, modern global warming is on track to increase surface temperatures by up to 4.4°C.
“Global warming of 9°C will not appear in the Anthropocene until at least 2500 in the worst-case scenario,” Kaiho predicts.
Kaiho does not deny that many extinctions are already occurring on land and in the sea due to climate change; he just doesn’t expect the same ratio of losses as before.
Still, it’s not just the degree of climate change that puts species at risk. The speed at which it occurs is vitally important.
The largest mass extinction event on Earth killed 95 percent of known species at the time and occurred more than 60,000 years ago about 250 million years ago. But current warming is occurring on a much shorter timescale thanks to human emissions of fossil fuels.
Perhaps more species will die in the sixth Earth extinction event, not because the magnitude of the warming is so great, but because the changes happened so quickly that many species could not 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.
Whichever way scientists crunch the data, it’s clear that many species are doomed unless we can stop climate change.
The exact percentage of losses and the timing of those losses remains open to debate.
The study was published in Biogeosciences.