Earth's Climate Evolution

C. P. Summerhayes, Colin P. Summerhayes

• Publisher: Wiley-Blackwell
• Year: 2015
• Print ISBN: 9781118897393
• eBook ISBN: 9781118897379
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Meteorology & Climatology

To understand climate change today, we first need to know how Earth's climate changed over the past 450 million years. Finding answers depends upon contributions from a wide range of sciences, not just the rock record uncovered by geologists. In Earth's Climate Evolution, Colin Summerhayes analyzes reports and records of past climate change dating back to the late 18th century to uncover key patterns in the climate system. The book will transform debate and set the agenda for the next generation of thought about future climate change.

The book takes a unique approach to the subject providing a description of the greenhouse and icehouse worlds of the past 450 million years since land plants emerged, ignoring major earlier glaciations like that of Snowball Earth, which occurred around 600 million years ago in a world free of land plants. It describes the evolution of thinking in palaeoclimatology and introduces the main players in the field and how their ideas were received and, in many cases, subsequently modified.  It records the arguments and discussions about the merits of different ideas along the way. It also includes several notes made from the author's own personal involvement in palaeoclimatological and palaeoceanographic studies, and from his experience of working alongside several of the major players in these fields in recent years.

This book will be an invaluable reference for both undergraduate and postgraduate students taking courses in related fields and will also be of interest to historians of science and/or geology, climatology and oceanography. It should also be of interest to the wider scientific and engineering community, high school science students, policy makers, and environmental NGOs.

Reviews:

"Outstanding in its presentation of the facts and a good read in the way that it intersperses the climate story with the author's own experiences. [This book] puts the climate story into a compelling geological history."
 -Dr. James Baker

"The book is written in very clear and concise prose, [and takes] original, enlightening, and engaging approach to talking about 'ideas' from the perspective of the scientists who promoted them."
 -Professor Christopher R. Scotese

"A thrilling ride through continental drift and its consequences."
- Professor Gerald R. North

"Written in a style and language which can be easily understood by laymen as well as scientists."
- Professor Dr Jörn Thiede

"What makes this book particularly distinctive is how well it builds in the narrative of change in ideas over time."
- Holocene book reviews, May 2016

"This is a fascinating book and the author's biographical approach gives it great human appeal."
- E Adlard

Chapter 1
Introduction

In almost every churchyard, you'll find gravestones so old that their inscriptions have disappeared. Over the years, drop after drop of a mild acid has eaten away the stone from which many old gravestones were carved, obliterating the names of those long gone. We know this mild acid as rainwater, formed by the condensation of water vapour containing traces of atmospheric gases like carbon dioxide (CO₂) and sulphur dioxide (SO₂). It's the gases that make it acid. Rain eats rock by weathering.

Weathering is fundamental to climate change. Over time, it moves mountains. Freezing and thawing cracks new mountain rocks apart. Roots penetrate cracks as plants grow. Rainwater penetrates surfaces, dissolving as it goes. The CO₂ in the dissolved products of weathering eventually reaches the sea, where it forms food for plankton, and the seabed, in the remains of dead organisms. Once there, it goes on to form the limestones and hydrocarbons of the future; one day, volcanoes will spew that CO₂ back into the atmosphere and the cycle will begin all over again.

The carbon cycle includes the actions of land plants, which extract CO₂ from the air by photosynthesis. When plants die, they rot, returning their CO₂ to the air. Some are buried, preserving their carbon from that same fate, until heat from the Earth's interior turns them back into CO₂, which returns to the air. This natural cycle has been in balance for millions of years. We have disturbed it by burning fossil carbon in the form of coal, oil or gas.

This book is the story of climate change as revealed by the geological record of the past 450 million years (450 Ma). It is a story of curiosity about how the world works and of ingenuity in tackling the almost unimaginably large challenge of understanding climate change. The task is complicated by the erratic nature of the geological record. Geology is like a book whose pages recount tales of the Earth's history. Each copy of this book has some pages missing. Fortunately, the American, African, Asian, Australasian and European editions all miss different pages. Combining them lets us assemble a good picture of how Earth's climate has changed through time. Year by year, the picture becomes clearer, as researchers develop new methods to probe its secrets.

As we explore the evolution of Earth's climate, we will follow the guidance of one of the giants of 18th-century science, Alexander von Humboldt, who wrote in 1788, ‘The most important result of research is to recognize oneness in multiplicity, to grasp comprehensively all individual constituents, and to analyze critically the details without being overwhelmed by their massiveness’¹. All too often, those who seek to deny the reality of modern climate change ignore his integrative approach to understanding nature by focusing on just one or two aspects where the evidence seems, at the moment, to be less than compelling.

Can the history of Earth's climate tell us anything about how it might evolve if we go on emitting gigatonnes (Gt) of CO₂ and other greenhouse gases into the atmosphere? That is the key question behind the title to this book. I wrote it because I have spent most of my career working on past climate change, and it worries me that few of the results of the growing body of research on that topic reach the general public. Even many professional Earth scientists I meet, from both academia and industry, know little of what the most up-to-date Earth science studies tell us about climate change and global warming. For the most part, they have specialised in those aspects of the Earth sciences that were relevant to their careers. Unfortunately, their undoubted expertise in these topics does not prevent some of them from displaying their ignorance of developments in the study of past climate change by trotting out the brainless mantra, ‘the climate is always changing’. Well, of course it is, but that ignores the all-important question: Why?

What we really need to know is in what ways the climate has been changing, at what rates, with what regional variability, and in response to what driving forces. With these facts, we can establish with reasonable certainty the natural variability of Earth's climate, and determine how it is most likely to evolve as we pump greenhouse gases into the atmosphere. This book attempts to address these issues in a way that should be readily understandable to anyone with a basic scientific education. It describes a voyage of discovery by scientists obsessed with exposing the deepest secrets of our changing climate through time. I hope that readers will find the tale as fascinating as I found the research that went into it.

The drive to understand climate change is an integral part of the basic human urge to understand our surroundings. As in all fields of science, the knowledge necessary to underpin that understanding accumulates gradually. At first we see dimly, but eventually the subject matter becomes clear. The process is a journey through time, in which each generation makes a contribution. Imagination and creativity play their parts. The road is punctuated by intellectual leaps. Exciting discoveries change its course from time to time. No one person could have discovered in his or her lifetime what we now know about the workings of the climate system. Thousands of scientists have added their pieces to the puzzle. Developing our present picture of how the climate system works has required contributions from an extraordinary range of different scientific disciplines, from astronomy to zoology. The breadth of topics that must be understood in order for us to have a complete picture has made the journey slow, and still makes full understanding of climate change and global warming difficult to grasp for those not committed to serious investigation of a very wide-ranging literature. The pace of advance is relentless, and for many it is difficult to keep up. And yet, as with most fields of scientific enquiry, there is still much to learn – mostly, these days, about progressively finer levels of detail. Uncertainties remain. We will never know everything. But we do know enough to make reasonably confident statements about what is happening now and what is likely to happen next. Looking back at the progress that has been made is like watching a timelapse film of the opening of a flower. Knowledge of the climate system unfolds through time, until we find ourselves at the doorstep of the present day and looking at the future.

While the story of Earth's climate evolution has a great deal to teach us, it is largely ignored in the ongoing debate on global warming. The idea of examining the past in order to discover what the future may hold is not a new one. It was first articulated in 1795 by one of the ‘fathers of geology’, James Hutton. But it is not something the general public hears much about when it comes to understanding global warming. This book is a wake-up call, introducing the reader to what the geological record tells us.

Information about the climate of the past is referred to as ‘palaeoclimate data’ (American spelling drops the second ‘a’). As it has mushroomed in recent years, it has come to claim more attention from Working Group I of the Intergovernmental Panel on Climate Change (IPCC). The Working Group comprises an international group of scientists, which surveys the published literature every 5 years or so to come up with a view on the current state of climate science. It has been reporting roughly every 5 years since its first report in 1990. Each of its past two reports, in 2007² and 2013³, incorporated a chapter on palaeoclimate data. The Working Group's report is referred to as a ‘consensus’, meaning the broad agreement of the group of scientists who worked on it. Just one chapter in a 1000-page report does not constitute a major review of Earth's climate evolution: the subject deserves a book of its own, and there are several, as you will see from the Appendix to the present book.

The study of past climates used to be the exclusive province of geologists. They would interpret past climate from the character of rocks: coals represented humid climates; polished three-sided pebbles and cross-bedded red-stained sands represented deserts; grooved rocks indicated the passage of glaciers; corals indicated tropical conditions; and so on. Since the 1950s, we have come to rely as well on geochemists using oxygen isotopes and the ratios of elements such as magnesium to calcium (Mg/Ca) to tell us about past ocean temperatures. And in recent years we have come to realise that cores of ice contain detailed records of past climate change, as well as bubbles of fossil air; glaciologists have joined the ranks.

Climate modellers have also contributed. Since the 1950s, our ability to use computers has advanced apace. We now use them not only to process palaeoclimate data and find correlations, but also to run numerical models of past climate systems, testing the results against data from the rock record. Applying numerical models to past climates that were much colder or much warmer than today's has an additional benefit: it helps climate modellers to test the robustness of the models they use to analyse today's climate and to project change into the future. One of my reasons for writing this book is to underscore how research into past climates by both of these research streams, the practical and the theoretical, adds to our confidence in understanding the workings of Earth's climate system and in predicting its likely future.

My take on the evolution of Earth's climate is coloured by my experience. Early in my geological career, I applied knowledge of how oceans and atmospheres work to interpret the role of past climates in governing the distribution of the phosphatic sediments that form the basis for much of the fertiliser industry. That work broadened into a study of how climate affects runoff from large rivers like the Nile and the Amazon, as well as the accumulation of sediments on the world's continental shelves. Working for Exxon Production Research Company (EPRCo) in Houston, Texas, in the mid-1970s, I developed a model for how climate controlled the distribution of petroleum source beds: rocks rich in organic remains that, when cooked deep in the subsurface, yield oil or gas. Explorers tested my model's predictions by drilling. Later, with the BP Research Company (BPRCo), I studied how the changing positions of past continents, along with changing sea levels and climates, affected the distribution and character of sources and reservoirs of oil and gas, as the basis for developing predictions for explorers to test by drilling.

In the late 1980s to mid-1990s, as director of the UK's main deep-sea research centre, the Institute of Oceanographic Sciences Deacon Laboratory, I learned a great deal more from my physical, biological and chemical oceanographer colleagues about the ocean's role in climate change. I applied that knowledge to analysing the response of the upwelling currents off Namibia and Portugal to the glacial-to-interglacial climate changes of the last Ice Age.

In order to develop accurate forecasts of climate change, one has to have an observing system, much like that used for weather forecasting. In 1997, I joined UNESCO's Intergovernmental Oceanographic Commission (IOC) to direct a programme aimed at developing a Global Ocean Observing System (GOOS), which would provide the ocean component of a Global Climate Observing System (GCOS). The task further broadened my understanding of climate science. Then, from 2004 to 2010, I directed the Antarctic research activities of the International Council for Science (ICSU), while based at the Scott Polar Research Institute of the University of Cambridge. There I was awarded emeritus status, starting in 2010. These recent appointments exposed me to the thinking of the polar science community about the role of ice in the climate system. Few people can have been as fortunate as I in being exposed to the current state of knowledge about the operations of the climate system from the perspectives of the ocean, the atmosphere, the ice and the geological record.

Because of that diverse background, I was asked to advise the Geological Society of London on climate change. Many of the world's major scientific bodies, including the US National Academy of Sciences and the UK's Royal Society, have felt moved in recent years to publish statements on the science of global warming as part of their remit to inform the public and policy makers about advances in science. The Geological Society of London became interested in 2009 in developing such a statement, and its then president, Professor Lynne Frostick, invited me to chair the group that would draft it. Entitled ‘Climate Change: Evidence from the Geological Record’, the statement was published on the Society's Web page⁴ and in its magazine, Geoscientist, towards the end of 2010⁵. I led basically the same team in writing an addendum to the statement in 2013, to show what advances had been made in the intervening 3 years and to provide a palaeoclimate-based statement that could be evaluated alongside the 5th Assessment Report of the IPCC's Working Group I, published in September 2013. We operated independently of the IPCC, and drew our own conclusions. The Society published the addendum in December 2013⁴.

As the Society's statement was being developed, I realised that it did not allow the space to r...

Table of contents

• Cover
• The Geological Time Scale for the Phanerozoic Aeon
• Title Page
• Copyright
• Table of Contents
• Dedication
• Author Biography
• Foreword
• Acknowledgements
• Chapter 1: Introduction
• Chapter 2: The Great Cooling
• Chapter 3: Ice Age Cycles
• Chapter 4: Trace Gases Warm the Planet
• Chapter 5: Moving Continents and Dating Rocks
• Chapter 6: Mapping Past Climates
• Chapter 7: Into the Icehouse
• Chapter 8: The Greenhouse Gas Theory Matures
• Chapter 9: Measuring and Modelling CO2 Back through Time
• Chapter 10: The Pulse of the Earth
• Chapter 11: Numerical Climate Models and Case Histories
• Chapter 12: Solving the Ice Age Mystery: The Deep-Ocean Solution
• Chapter 13: Solving the Ice Age Mystery: The Ice Core Tale
• Chapter 14: The Holocene Interglacial
• Chapter 15: Medieval Warming, the Little Ice Age and the Sun
• Chapter 16: Putting It All Together
• Appendix A: Further Reading
• Appendix B: List of Figure Sources and Attributions
• Index
• End User License Agreement