PETM has some similarities to current climate change, with key differences as well. Multiple lines of evidence suggest the rapid warming millions of years ago was triggered by a large amount of carbon released into the atmosphere, but the exact cause is unclear. During that time, temperatures climbed by about 5 to 8 degrees Celsius over just tens of thousands of years—a geologic blink of an eye. Today's temperatures could be warming a similar amount, but the change is happening over a couple hundred years and carbon dioxide release is up to an order of magnitude faster, Dickson says. Additionally, the PETM was during an already balmy "greenhouse" climate, a period in Earth's cycle characterized by warm temperatures and few large ice sheets. In contrast, the planet currently has an "icehouse" climate, but modern climate change attributed to human activity has driven the planet away from a possible ice age.
"By all accounts, what we are seeing today is more extreme," Dickson says. The ancient ocean environment was also certainly affected by a different pattern of ocean circulation than what researchers see today, he explains. However, very little is known about the specifics of that pattern. Even with these caveats, exploring the PETM gives scientists a clearer understanding of how Earth responds to climate changes—and may furnish a useful new measure to assess where we stand in the current warming trend.