PETM

The Paleocene-Eocene Thermal Maximum (PETM) is a major global warming event that occurred about 56 million years ago, at the boundary between the Paleocene and Eocene epochs. It is marked by a rapid rise in Earth’s average surface temperature and a large perturbation of the carbon cycle, evidenced in marine and terrestrial proxies.

Climate evidence indicates global mean temperature rose by roughly 5 to 8 degrees Celsius within a few thousand years, with warming lasting on the order of 100,000 to 200,000 years. The onset is accompanied by a pronounced negative excursion in carbon isotopes (δ13C) in carbonates and organic matter, signaling a substantial input of light carbon to the atmosphere and oceans.

Causes of the carbon input are still debated. Leading hypotheses include release of methane from marine hydrates and/or large-scale disturbance of peatlands and coal deposits, potentially aided by volcanic and tectonic processes. The total carbon released is estimated to be several thousand gigatons.

Environmental impacts were broad. Ocean acidification occurred, affecting carbonate chemistry and calcifying organisms; deep-sea and shallow-water foraminifera experienced turnover and range shifts. Terrestrial ecosystems underwent faunal and floral changes, with rapid evolution and the expansion of tropical-adapted fauna toward higher latitudes; forests grew and modern mammal groups proliferated in the Eocene.

Significance of the PETM lies in its role as a well-documented ancient example of rapid climate change and carbon-cycle disruption. It provides a benchmark for understanding potential responses of the climate system to large carbon inputs and helps inform models and risk assessments related to contemporary anthropogenic emissions.