Friday, October 16, 2015

Modeling the Transition to a Hot Greenhouse Climate at the Permian Triassic Boundary

Transition into a Hothouse World at the Permian–Triassic boundary—A model study


Winguth et al


The Permian–Triassic boundary (PTB, ~ 252.3 Ma) marks the largest mass extinction of the Phanerozoic, with a loss of more than 90% of marine organisms, and is characterized by lethally hot surface temperatures. The PTB global warming has been linked to greenhouse gas emissions from the Siberian Traps and associated coal-bed intrusions and likely led to severe environmental consequences, such as ocean acidification, a decline in the marine productivity, and extensive hypoxia. In order to understand these changes, feedbacks in the climate system have been explored with sensitivity climate simulations and compared to temperature proxies from the sedimentary record. The response of the PTB ocean circulation to an atmospheric perturbation of ~ 5000 Pg C, comparable to Earth's total fossil fuel inventory, leads to a global temperature increase by 3–4 °C and an increase in ocean stratification. The pole-to-equator temperature gradient decreases by 2 °C with an increase in CO2-radiative forcing, predominately due to snow albedo feedbacks over Gondwana. The greenhouse-induced warming would have led to a weakening of the Hadley cell and an associated decrease in the trade winds and equatorial primary productivity. These climatic changes might have been amplified by cloud-feedback processes. A reduced concentration of cloud condensation nuclei due to a biologic decline of dimethylsulfide caused by the temperature stress or changes in airborne mineral particles could have reduced the cloud albedo, particularly in high latitudes. Results from a climate simulation with reduced cloud albedo suggest a polar warming of up to 7 °C and a reduction of the pole-to-equator temperature gradient by ~ 4 °C in addition to the reduction caused by the increase in greenhouse-induced radiative forcing. The scenario with reduced cloud albedo further leads to an increase in ocean stratification and widespread low-oxygen concentrations in the Panthalassa during the Early Triassic.

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