HOTHOUSE CLIMATE AT THE END-PERMIAN AND IMPLICATIONS FOR FUTURE CLIMATE CHANGE AND MASS EXTINCTION

The Permian period experienced a large climate transition from the cold-house world during the Early Permian with an ice-covered Gondwanaland to a nearly ice-free world near the Permian-Triassic transition. Anthropogenic emissions from fossil fuel burning over the next centuries will probably lead to a transition into a hothouse world with an ice-free climate comparable to that at the Permian-Triassic Boundary (PTB).

In this paper, we analyze the climate sensitivity and pole-to-equator heat transport of paleoclimate models with regard to feedbacks for the PTB and compare them with climate sensitivity as derived from the geological record in order to highlight uncertainties associated with the model predictions and reconstructions and their implications for the evolution of future climate change and mass extinction.

Comprehensive climate models, like NCAR’s CCSM3 and CESM1, indicate a high sensitivity of ocean stratification and deep-sea anoxia to changes in the cloud optical depth and associated strength of the ocean heat transport. For example, a 20% reduction in the poleward ocean heat transport can lead to a shutdown of the oceanic overturning circulation.

Despite these tipping points revealed by the climate simulations it is difficult to assess the speed at which slow feedbacks, like the decline of the ice sheets, accelerate the transition into a hothouse world.