Climate response at the Paleocene-Eocene Thermal Maximum to greenhouse gas forcing - A model study with CCSM3

In this study, the PETM climate is investigated using the Community Climate System Model (CCSM3) with atmospheric CO₂ concentrations of 4×, 8×, and 16× the preindustrial value. Simulated climate change from 4× to 8× atmospheric CO₂ concentration, possibly corresponding to an environmental precursor of the PETM event, leads to a warming of the North Atlantic Ocean Intermediate-Water masses, thus lowering the critical depth for methane hydrate destabilization by 500 m.

A further increase from 8× to 16×CO₂, analogous to a possible massive methane hydrate release, results in global oceanic warming and stratification. The increase in the radiative surface warming, especially at high latitudes, is partially offset by a decrease in the ocean heat transport due to a reduced overturning circulation. Surface temperature values simulated in the 16×CO₂ PETM run represent the closest match to surface temperature reconstructions from proxies for this period.