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Annual Meeting 2014: Annual Address

Understanding Ancient Earth Climates and Environments using Models and Data

Professor Alan M. Haywood

School of Earth & Environment, Woodhouse Lane, University of Leeds, Leeds, LS29JT, UK.

Geology and palaeontology have demonstrated that climate is not stable. We know that climate change occurs over a variety of timescales (e.g. tectonic, orbital, millennial, centennial, decadal, sub-decadal). The fossil record and advanced numerical models of climate, and increasingly Earth system, are gradually lifting the veil on the mysteries of Earth climatic and environmental evolution and variability. Studies have focussed on understanding the drivers for changes in mean climate state as well as the causes and consequences of climatic transitions and rapid climate change. In this talk we will explore how models and data have been used successfully together to better understand three distinctly different intervals in Earth history, each presenting their own unique challenges, scientific questions and benefits.

The first case study is focussed on the relative role of climate and environmental change versus human influence on the extinction of Late Quaternary mega fauna. Despite decades of research, the roles of climate and humans in driving the dramatic extinctions of large-bodied mammals during the Late Quaternary period remain contentious. Models and data have shown that climate has been a major driver of population change over the past 50,000 years. However, species respond differently to the effects of climatic shifts, habitat redistribution and human encroachment. Although climate change alone can explain the extinction of some species, such as Eurasian musk ox and woolly rhinoceros, a combination of climatic and anthropogenic effects appears to be responsible for the extinction of others.

The second case study focusses on quantifying the equilibrium response of global temperatures to an increase in atmospheric carbon dioxide concentrations, which is one of the cornerstones of climate research. Components of the Earth’s climate system that vary over long timescales, such as ice sheets and vegetation, have an important effect on this temperature sensitivity, but are normally neglected. Climate models, using geological derived boundary conditions (vegetation and ice cover), have been used to simulate the climate of the mid-Pliocene warm period, and to analyse the forcing and feedbacks that contributed to the relatively warm temperatures. Estimates suggest that the response of the Earth system to elevated atmospheric carbon dioxide concentrations is 30 to 50% greater than the response based on those fast-adjusting components of the climate system that are used traditionally to estimate climate sensitivity. This suggests that targets for the long-term stabilization of atmospheric greenhouse-gas concentrations aimed at preventing a dangerous human interference with the climate system should take into account this higher sensitivity of the Earth system.

The final case study focusses on the Eocene to Oligocene transition and the shift between a greenhouse and ice house state ~33 million years ago. The development of the Antarctic Circumpolar Current (ACC) has been linked to the thermal isolation and growth of the Antarctic Ice Sheet at the time yet the development of the ACC during the Cenozoic is controversial in terms of timing and its role in major climate transitions. Climate model results show that that a coherent ACC was not possible during the Oligocene due to Australasian palaeogeography, despite deep water connections through the Drake Passage and Tasman Gateway and the initiation of Antarctic glaciation. These simulations of ocean currents compare well to marine proxy records records relating to the physical oceanography of the Oligocene and provide a framework for understanding apparently contradictory dating of the initiation of the ACC.

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