A massive release of greenhouse gases, likely triggered by volcanic activity, caused a period of extreme global warming known as the Paleocene-Eocene Thermal Maximum (PETM) about 56 million years ago. A new study now confirms that the PETM was preceded by a smaller episode of warming and ocean acidification caused by a shorter burst of carbon emissions. The short-lived precursor event represents what might happen if current emissions can be shut down quickly, while the much more extreme global warming of the PETM shows the consequences of continuing to release carbon into the atmosphere at the current rate.