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Earth's Climate Evolution

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Ice sheets are melting. “Global warming deniers are fond of saying “the climate is always changing”. Well, yes it is, but why, and how, and how much? Studying the geological and ice core record helps us to see how variable our climate is, and what makes it so, which helps to explain what is happening now and what may happen next. The past 30 years have seen especially dramatic advances in our knowledge of past climatic variability, from studies of ice cores, along with piston cores and drill cores of marine sediment. A key emerging message is that our climate operates within a narrow natural envelope. Over the past 2000 years we have been at the cold end of the Holocene Neoglacial period, driven there by changes in Earth’s orbit. Peaks in solar output gave us the Medieval Warm Period and the warming from 1900 to 1945, but since 1960 solar output has been flat or in decline, while temperatures have gone on rising even though the orbital data tell us we should still be in the cool Neoglacial. We have been driven outside the natural climate envelope by our emissions of CO2 . This geologically based information is independent of numerical climate models, yet supports them. The rock and ice records tell us that further increasing CO2 will drive up temperature and sea level.

Colin Summerhayes is a marine geochemist with expertise in determining past climates from the characteristics of marine sediments. He is an Emeritus Associate at the Scott Polar Research Institute of the University of Cambridge. Formerly he was Executive Director of the International Council for Science’s Scientific Committee on Antarctic Research (SCAR), Director of the Global Ocean Observing System (GOOS) Project at UNESCO ’s Intergovernmental Oceanographic Commission in Paris, Director of the UK’s Institute of Oceanographic Sciences Deacon Laboratory (Wormley), and Deputy Director of what is now the National Oceanography Centre.

His books include “Oceanography – an Illustrated Guide”, “Oceans 2020 – Science, Trends and the Challenge of Sustainability”, “Antarctic climate Change and the Environment”, and (in press) “Earth’s Climate Evolution

This talk is part of the Friends of Scott Polar Research Institute lecture series series.

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