The event is known as the Palaeocene-Eocene Thermal Maximum (PETM) but the cause of the warming is still debated. Huge amounts of carbon entered into the atmosphere at the time along with methane.

Based on the geological record, we know that Earth warmed by more than 5 to 8 °C during the period known as the Paleocene-Eocene Thermal Maximum. We also understand that dramatic changes in Earth ...