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ABSTRACT
The Paleocene-Eocene Thermal Maximum (PETM; 55 Ma) is of particular interest since it is regarded as a suitable analog to future climate change. 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.
Simulated PETM precipitation, characterized by a slight northward shift of the intertropical convergence zone, increases at higher CO2 concentrations, especially for the northern midlatitudes as well as the high latitudes in both hemispheres. Data-inferred precipitation values and grathents for North America and Spain, for instance, are in good agreement with the 16×CO2 simulation. Increasing atmospheric CO2 concentrations might also have favored the release of terrestrial methane through warmer and wetter conditions over land, thus reinforcing the greenhouse gas concentration increase.
1. Introduction
Superimposed on a long-term warming trend from the late Paleocene through the early Eocene is a prominent global hyperthermal at the Paleocene-Eocene boundary (55 Ma), referred to as the Paleocene-Eocene Thermal Maximum (PETM). Surface temperatures increased by 5°C in the tropics (Tripati and Elderfield 2005; Zachos et al. 2005) and midlatitudes (Wing et al. 2005) and by 6°-8°C in the Arctic and sub-Antarctic (Kennett and Stott 1991; Thomas et al. 2000; Sluijs et al. 2006; Hollis et al. 2009) and deep-sea temperatures increased by 4°-6°C (Tripati and Elderfield 2005) relative to Paleocene temperatures (see Fig. 1). At the same time, global humidity and precipitation patterns changed (Robert and Kennett 1994; Wing et al. 2005; Pagani et al. 2006a; Brinkhuis et al. 2006; Sluijs et al. 2008a),...