How Unusual Was the Paleocene‐Eocene Thermal Maximum?

Abstract The Paleocene‐Eocene Thermal Maximum (PETM) was an extreme fluctuation of Earth's climate and a potential analog for future unmitigated anthropogenic climate change, but whose cause is debated. We show that fluctuations in Cenozoic benthic foraminiferal C and O follow a Laplace distribution. We present a simple model to explain this behavior: isotopic fluctuations respond to big and small “kicks” in the same way. We then use this to develop an expectation for the largest Cenozoic C and O fluctuations. While the other hyperthermals of the early Cenozoic are encompassed the expected range, we quantify that the PETM isotopic signatures were larger than these expectations, by 1.15 0.25‰ for O and 1.75 0.24‰ for C. This supports the view that the PETM is an extreme outlier amongst Cenozoic perturbations to the climate system and thereby was likely triggered by a large and unusual external perturbation.