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Developments in different branches of science, including geology, have provided us with the basis for a coherent theory of climate change. The geologists of the 19th century were puzzled by the 'Great Cooling' that characterized the Tertiary Era. They were also puzzled by erratic blocks. Buckland thought them dumped by Noah's flood, Lyell thought them dumped by icebergs, Agassiz preferred ice sheets, and won the day.  In the 1860s Tyndall found that CO₂ absorbed and re-emitted heat, so could explain past climate change. In the 1890s Arrhenius calculated how changes in CO₂ might explain glacials and interglacials. By 1899 T.C. Chamberlin converted that into a geological theory of global climate.

We now know that a decline in CO₂ caused the 'Great Cooling'. Its record differs from place to place because the continents have moved. Lyell realised in 1830 that the motions of continents through climate zones could explain past climate change, an idea perfected by Wegener in the 1920s, underpinned by palaeomagnetic data in the 1950s, and reinforced by plate tectonic theory in the 1960s.

Attempts to attribute Ice Age variability to celestial mechanics began in 1830, advanced with Croll in the 1860s, Milankovitch in the 1920s, and Andre Berger in the 1970s. Isotope geochemists began unravelling the secrets of climate change in the 1950s, expanding their work through access to deep ocean cores from 1968 on, and to ice cores from the 1980s. Linking isotopic changes in sediments to celestial mechanics was as big a breakthrough as plate tectonics. We can now use isotopes to investigate the centennial variability of the Sun. 

We have come a long way from the notion that erratic blocks of rock on British hills were deposited by Noah's flood. The past 20 years have seen dramatic advances in our knowledge of the variability of past climate, and its causes, which underpins understanding what our climate is doing now and may do in the future (following Hutton's dictum that the past and the present are the keys to what happens next). These advances, many of them only reported in scientific journals, deserve to be more widely known. They show that our climate operates within narrow natural envelopes. We should still be in the Little Ice Age envelope, but our emissions have moved our climate into new territory. Man has become a geological agent.

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Speaker

Colin Summerhayes

Scott Polar Research Institute, University of Cambridge 

Dr Colin Summerhayes is a marine geochemist with expertise in determining past climates from the characteristics of marine sediments. He is an Emeritus Associate undertaking research on climate history at the Scott Polar Research Institute of the University of Cambridge. Formerly he was Executive Director of the "Scientific Committee on Antarctic Research" for the International Council for Science (2004-2010); Director of the Global Ocean Observing System for UNESCO's Intergovernmental Oceanographic Commission in Paris (1997-2004); Director of the UK's Institute of Oceanographic Sciences Deacon Laboratory (Wormley) (1988-1997); and Deputy Director of the National Oceanography Centre (Southampton) (1995-1997).

He has worked in academia, government and industry, spending 6 years each with BP and EXXON. His books include: "Earth's Climate Evolution" (2015); "Antarctic climate Change and the Environment" (2009); "Oceans 2020 - Science, Trends and the Challenge of Sustainability" (2002); "Oceanography - an Illustrated Guide" (1996); "Upwelling in the Ocean" (1995); "Upwelling Systems" (1992); and North Atlantic Palaeoceanography" (1986). He is a former Vice President of the Geological Society of London, and Past President of the Society for Underwater Technology.

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