PETM

Also: Palaeocene-Eocene Thermal Maximum, Palaeocene Eocene Thermal Maximum

Palaeocene-Eocene Thermal Maximum

The Paleocene-Eocene Thermal Maximum (PETM) was a period of natural global warming that took place almost 56 million years ago.  It came at a time when the atmospheric concentration of CO2 was already higher than today, and global temperatures also much warmer. The PETM warming was a roughly 200,000-year long event where global temperatures rose by 6–8°C, and is thought to have been caused by a massive injection of CO2 into the atmosphere.