The fifth mass extinction event occurred some 66 million years ago, wiping out the dinosaurs, which probably was not a bad thing for the survival of mammals like us. We like to listen to T-Rex not get eaten by one.

Now Prof. Kunio Kaiho, a Japanese climate scientist from Tohoku University, has proposed a relationship between extinction magnitude and climate change (https://bg.copernicus.org/articles/19/3369/2022/) whereby significant species loss will occur if the earth's surface temperature warms or cools by c. 7-9 degrees.

According to Science Alert (https://www.sciencealert.com/study-links-bigger-temperature-changes-with-larger-extinction-events):

That's much higher than previous estimates, which suggest a temperature of 5.2°C would result in a major marine mass extinction, on par with the previous 'big five'. To put that in perspective, by the end of the century, modern global warming is on track to increase surface temperatures by as much as 4.4°C.  "The 9°C global warming will not appear in the Anthropocene at least till 2500 under the worst scenario," Kaiho predicts.

Greta Thunberg has pledged to travel to Japan by pogo stick to personally chastise Mr Kaiho for his unhelpful contribution to the debate as by 2500 she too will be extinct (along with me and you dear reader).