It is often said that humans have caused the Earth to warm at an unprecedented rate. However researchers have discovered another period, some 55m years ago, when massive volcanic eruptions pumped so much carbon into the atmosphere that the planet warmed at what geologists would think of as breakneck speed.

The good news is that most plants and animals survived the warm spell. The planet has experienced several mass extinctions – and this wasn’t one of them. But there’s a catch: even after carbon levels returned to their previous levels, the climate took 200,000 years to return to normal.

Geologists have a name for this earlier period of sudden warming: the Palaeocene-Eocene Thermal Maximum. The PETM, as we’ll call it, occurred 55.5–55.3 million years ago. According to new research published in the journal Nature Geoscience it involved global warming of between 5 and 8°C over a period of 200,000 years.