ncreases in carbon emissions caused by human activity are “outpacing” the rate of CO2 emissions during an ancient global-warming event that sparked mass extinction, researchers have warned.

A study, published in the journal Proceedings of the National Academy of Sciences, found that a rapid warming event which took place more than 55 million years ago and caused extinction in the deep sea saw carbon emissions rise at a much slower rate than today.

Researchers also found that the event known as the Paleocene-Eocene Thermal Maximum (PETM) was likely caused by major volcanic activity.