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Earth's Climate Evolution.

EARTH'S CLIMATE EVOLUTION

Colin P. Summerhayes, 2015, 394 pp., $79.95, hardbound, Wiley-Blackwell, ISBN 978-1-118-89739-3

Climate science is one of the most active fields that is being explored by researchers in meteorology, oceanography, and many other disciplines. Central to these endeavors are the insights provided by climate models. A growing area of interest in climate modeling is the simulation of past climates of our planet. This new thrust is essential for providing context for climate change evolving into the future. It is important to learn the status of our understanding of paleoclimatology from the scientists who have provided this body of work. Plucking out the salient details from geological research is not usually so easy for the modeler.

This book by Colin Summerhayes provides an excellent source of information about paleoclimatology and insight for researchers across a wide spectrum of backgrounds. It presents the history of the discipline of paleoclimatology as it has developed over the last few centuries. Concurrently, Summerhayes uses the marine geologist's lens to explain how we have come to understand the past climates of Earth. The author is a fellow traveler along the trajectory of that history. The story of the overheated controversies among geologists and their resolution amount to one of the marvels in the history of science, and it is worth reading by any scientist.

The book begins with a great puzzle in the nineteenth century related to glaciers in the Alps. Did these ice sheets expanding from the mountains into the plains explain the many odd occurrences, such as large boulders lying isolated in the plains? Or was it the great flood of Noah that brought those boulders?

More data and understanding led to the idea of ice age cycles. Did the cycles actually exist, and what might have caused them? Theories began to emerge--such as Croll's--that there might be an astronomical explanation. Other theories of the early twentieth century included the role of trace gases and the greenhouse effect as a stimulant of climate change.

This is just the beginning of a thrilling ride through continental drift and its consequences--how the location and configuration of the continents can have a drastic effect on climate. Drilling cores from the ocean floor became the dominant new source of information. We learn from these seafloor data that the climate does have a pulse marked by the ebb and flow of continental ice sheets.

Thanks to the digital computer in the second half of the twentieth century we find improvements of our understanding of the greenhouse effect. On the observational side we find a new tool: the drilling of ice cores and the conversion of that data into a history of trace gases in the atmosphere and the temperature at the surface going back 800,000 years. The author explains how these advances came about and how they worked. Other markers are discovered, such as indicators of past sea levels from coral terraces and their correlation with the volume of ice on the land.

We are taken through the quantitative timing of the great glaciations and their connection with the calculated changes in Earth's orbital elements. We also find that C[O.sub.2] and other greenhouse gases change at the same frequencies as the ice volume and the orbital elements. Finally we arrive at the Holocene (the last 10,000 years) and its very mild climate, at least up until the most recent warming trend. The author discusses the likely causes of the recent warming.

Summerhayes tells his story without equations, but his explanations are very carefully laid out in such a way that an outsider can follow without difficulty. Many clearly drafted graphics are included, and hundreds of references to original works at the ends of each chapter will entice the interested reader.

I enjoyed the short biographical sketches of the heroes, many with thumbnail portraits. The lives and contributions of these giants are fun to read and they bring to life the thrill of discovery and the many fierce battles that eventually led to the solution of the problems. I met quite a few of them in my own brushes with paleoclimatology. My admiration of them was renewed and amplified as I read.

Perhaps I am an old curmudgeon, but I think there are many problems that are yet to be solved in the give-and-take between climate theory (including climate models) and the record. I am not sure we can yet explain how an ice sheet gets started after being nudged by the orbital element shifts. The astronomical theory provides a pacemaker for the ice ages, but some parts of the mechanism are still missing. Even if we allow the greenhouse gases to enhance the response, it does not seem to be enough. I am also not so sure of the Sun's changes in brightness as an explanation for the Medieval Warm Period or the so-called Little Ice Age.

Reading this great history reminds me of the explosive changes during the last century in physics, chemistry, mathematics, and biology, to name just a few. Reading and contemplating history provides us with context within which we live and work. This book helps.

--Gerald R. North

Gerald R. North is a research professor in the Department of Atmospheric Sciences at Texas A&M University.
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Author:North, Gerald R.
Publication:Bulletin of the American Meteorological Society
Article Type:Book review
Date:Dec 1, 2016
Words:879
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