Te Geological Timescale for the Phanerozoic Eon and the Neoproterozoic Era of the Proterozoic Eon (in millions of years, rounded up or down)
yrs
From Cohen, K.M., Finney, S.C., Gibbard, P.L., and Fan, J.-X. (2013; updated 2018) Te ICS International Chronostratigraphic Chart. Episodes 36, 199–204.
The Icy Planet Saving
Earth’s Refrigerator
Colin Summerhayes
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DOI: 10.1093/oso/9780197627983.001.0001
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This book is dedicated to all our children, grandchildren, and great-grandchildren and their descendants, who will have to live with the consequences of the overheating of our atmosphere and our ocean and the melting of our ice through the global pollution we and our predecessors have caused by the seemingly innocuous act of burning coal, oil, and natural gas.
I would also like to pay tribute here to some of the often overlooked female scientists who are making a huge difference in studies of polar climate and past climates (which provide examples of what may happen if we fail to limit global overheating), in the hope that it will encourage yet more young women to enter these challenging research fields to follow these great examples: Jane Francis, Maureen Raymo, Valérie Masson-Delmotte, Dorthe Dahl-Jensen, and Robin Bell.
Preface
Human influence has warmed the climate at a rate that is unprecedented in at least the last 2000 years. [As a result] In 2011–2020, annual average Arctic sea ice area reached its lowest level since at least 1850. Late summer Arctic sea ice area was smaller than at any time in at least the past 1000 years. The global nature of glacier retreat, with almost all of the world’s glaciers retreating synchronously since the 1950s is unprecedented in at least the last 2000 years.
IPCC, 2021 (in press): Summary for policymakers. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press (ipcc.ch).
Making sure our planet remains habitable demands the same ambition, organization, planning, bottom-up experimentation, public-private risk sharing and sense of purpose and urgency as the Apollo project [which put men on the Moon].
Mariana Mazzucato (2018) The Value of Everything: Making and Taking in the Global Economy. Penguin, 358pp.
The damage we are doing is no longer incremental but exponential, and we are fast reaching a tipping point . . . change is possible when you set your mind to it . . . [we need] collective ambition, and a can-do-spirit, to find solutions . . . urgency + optimism = action.
HRH Prince William (2021) Introduction. In Butfield, C., and Hughes, J., with Pearce, F., Earthshot: How to Save Our Planet. John Murray, vii–xiv.
Our Global Refrigerator
For most of us, the world’s icy wastes are outside our experience, readily available only on TV, and for the few who like to ski in the winter or climb mountains in the summer. Most people never get to see ice, unless it’s in a drink. Being out of sight, it is largely out of mind. Most of us never give a thought to the fact that people live in the Arctic, and that scientists work on the Antarctic ice sheet. Tese realms are far away, the conditions are extreme, very few people live there, and even getting there is both time consuming and costly. Why do it, just to be uncomfortable? And yet, when land ice melts, the oceans rise. No matter how far away you live from melting ice, your sea level is likely to rise to some degree depending on where you live. Coastal
populations will bear the brunt. Te few places where that is not the case include, for instance, northern North America centered on Hudson Bay, and Scandinavia centered on the Baltic Sea coast. Tey are now popping up like corks—although at geological (or should I say glacial) rates—having shed the ice sheets that weighed them down during the peak of the Ice Age 20,000 years ago. Ongoing melting in Greenland and Antarctica will make their margins rise too, hence sea level will fall along their coasts in due course.
Why should we care about ice melt? It may come a surprise to you to learn just how icy our planet is. But all that ice is what gives us a global climate suitable for life as we know it. Te ice is Earth’s refrigerator—cooling our planetary temperatures to bearable levels, and, in the process, keeping our sea levels stable.
Why should we worry? Aren’t the rates of temperature rise and sea level rise extremely slow? Tis is indeed the impression the members of the public who attend my lectures have. But to scientists assessing the data, the rates of rise of temperature and sea level are increasing with time and beginning to be “fast” compared with natural events in the distant past. I am reminded of the boiled frog syndrome: put a frog into cold water and heat the pan and the frog may slowly cook; pop him into a pan of hot water and he’ll jump right out. We are now the frogs in the pan of cold water, and the heat is rising. If we do not save our refrigerator, we will cook.
Our climate baseline is slowly shifing, almost imperceptibly to the hypothetical “man in the street.” In contrast, the modern climate scientist sees a signifcant upward trend in temperature and sea level. Members of the public can fnd it confusing when their local climate cools in response to some temporary regional or global wobble that might last a decade or so. As a young man I experienced the European cold of the early 1960s. Some of the climate scientists of the day thought that it might presage a new Ice Age. But by the time my children were born, that cold had passed. My grandchildren, in turn, have been born into a world warmer than the one their parents grew up in. With the beneft of hindsight we now know that the cooling of the 1960s was a temporary blip driven by natural decadal variation and exacerbated by the dirty air our factory and power station chimneys emitted before Clean Air legislation forced them to clean up their acts. It has been followed since 1970 by a substantial global warming trend punctuated from time to time by other brief natural coolings or pauses in the upward trajectory. Global overheating is now melting polar ice at a rate that has accelerated since 1980. Te rising heat and the ice are not in equilibrium, because it takes a long time to melt ice, and because 90% of the heat of global warming is trapped in the oceans. Tink how long the ice in your drink lasts, even on a hot day. Even if we stopped warming the world tomorrow by stabilizing the climate at some arbitrary level, like an average global temperature of 1.5°C, the ice sheets would go on melting for centuries, making sea level rise more. Tink about it this way: a stable warm climate will pour heat every year into yet more ice melt, losing us progressively more refective sea ice every year, which in turn will expose more ocean to warming, creating a feedback process that will melt yet more sea ice, and so on.
By how much will sea level rise? Conservative estimates put the global average rise by 2100 at close to half a meter (1.6 f) compared with what it was in 1900. It is already 20 cm (8 in) above the level of 1900. Analogies with the geological record suggest that a heating of 2°C–3°C (3.6°F –5.4°F) above the average for 1900 will generate a rise of 10+ m (33+ f) in the 300-year time frame. If this happened overnight, as in a tsunami, it would be a catastrophe. Te actual rate of rise is slow, at close to 4 mm (0.16in)/ year, but gradually speeding up. I call this situation a “creeping catastrophe,” because its ultimate efects would be catastrophic for the people, villages, towns, and cities in coastal regions if nothing were done to stave of these efects in the meantime.1
Orrin Pilkey suggests we should think of this slow rise as a slow tsunami.2 Te closest I can come to imagining the efect would be to remind readers that there once was a population of paleolithic people living and hunting on what is now a major fshing ground in the North Sea—the Dogger Bank. Te bank slowly drowned as sea level rose with the ice melt that began 20,000 years ago at the end of the last Ice Age. Fishermen now occasionally catch the remains of mammoths, or ancient hand axes in their nets on the Dogger Bank. Nobody lives there now.
We humans have been around on the planet for just 300,000 years. During most of that time our forefathers were hunter-gatherers living mostly in Africa and Arabia. Tose who forayed into more northern regions would have bumped up against the tundra, which covered much of Europe during the cold periods of advancing ice sheets that extended as far south as Kansas City in the United States and north London in the United Kingdom and covered most of the Alps. Looking across much of Europe, Asia, and North America, it is hard to believe that not very long ago the places many of us live in were covered either by an ice sheet or by the tundra along its southern edge. Tose of us who live in these formerly icy regions are all immigrants to previously empty lands.
From time to time our ancestors would have experienced the quite rapid coolings typical of Northern Hemisphere climate changes during the Ice Age, which tended to keep populations well south of the Pyrenees, the Alps, and the Himalayas. In warmer periods they would have migrated north following game—especially the migrating reindeer and bison depicted on the walls of caves in southern France and Spain. Te most recent of those warmer periods covered the past 12,000 years, during which human civilization developed, stimulated by the invention of agriculture, which allowed early humans to escape from their hunter-gatherer lifestyle.
As our climate emerged from the peak of Ice Age cold some 20,000 years ago, ice melted and sea level rose. Global temperatures at mid-latitudes stayed fairly constant for most of the past 12,000 years, but over that same time in the polar regions global heat frst climbed toward an optimum as ice sheets melted away and sea level rose. Once the major ice sheets were gone, the polar climate began to cool, and the ice began to regrow over the past 4,000 years. Since 1900 both the “fat” climate trend of the mid-latitudes and the declining climate trend of the polar regions have gone into reverse.
Our current overheating is now attacking Earth’s ice cover. We can expect that (as in the past) there will be a lag in ice melt behind the present rise in temperature, which will last for centuries. Although our Paleolithic ancestors at the northern edge of their European range might have occasionally experienced changes as fast as the present one, this is the frst time our settled global civilization has experienced such a change in its 10,000-year history. As yet there is every sign that our current overheating will continue way beyond what our ancestors experienced in their 300,000-year history— unless we act to stop the change that we have created through polluting the air with combustion products from the burning of coal, oil, and natural gas.
To stop the rot we are going to have to work together collectively and cooperatively across the globe to manage our planetary climate. We have already done this in a small way through the actions needed to close the ozone hole over Antarctica. Managing the climate of the entire planet is a far greater challenge. Will we measure up to it, or will our tribalist nationalism get in the way? Will the rich nations that have created the global overheating help the poor nations who sufer the most from its efects?
Big decisions are called for. And we have already stepped back from the brink several times, afraid to go far enough, at previous Conferences of the Parties (COPs) to the UN Framework Convention on Climate Change, like the one in Glasgow in November 2021. I speak from experience, having attended the 15th COP in Copenhagen in December 2009. Te road to hell, they say, is paved with good intentions. Te time has come for actions. We must take the plunge.
Tis book will explore multiple questions about the world’s icy places. Just how cold are they? We now know that sea ice melts increasingly in the summer in the Arctic, but not in the Antarctic—why not? Is it because Antarctica is colder than the Arctic, and if so, why? And what does it matter in the global scheme of things? What is permafrost, and where is it, and why should we care that it’s melting? Are glaciers in the world’s mountains really in decline? By how much, and how fast, and where were they in the past when it was much colder? What does their retreat bode for those who rely for water on summer ice and snow melt? What does drilling through the ice tell us about past climate change? And what bearing does that knowledge have on our understanding of today’s climate? Are the Arctic and the Antarctic really connected directly through the ocean? Wouldn’t that be amazing if it were true? Well, it is true, but the connections have changed with time. Tis is all part of the great climate change story that we will be exploring in these pages.
We shall also see what it’s like in these icy places. How do scientists survive in Antarctica, and under what conditions? What are they measuring when they’re down there for the winter, and why are they doing it? What’s the point? What are tourists going to see in the Arctic and the Antarctic? Is it just the scenery that motivates them, or a desire to see these places before they melt away? And how do their visits afect the rest of us? My personal view is that such visits make people ambassadors for climate and environmental science when they get back home.
How dangerous is it to work in a mainly icy world—do people still fall into crevasses? Given how easy transportation and communication are there now, what was it like for the early explorers, and why did anyone go exploring in these places anyway? Tey knew it was dangerous, they had no maps, and if something went wrong they’d die! Brave men hazarded much to enlighten us, and some did die in the process. Men, yes, because early exploration wasn’t a woman’s game. Since those early maledominated years, women have become an accepted feature of Arctic and Antarctic science, especially in recent decades, and rightly so.
Questions like these stimulate the imagination, as does the wonderful if sometimes desolate scenery of the ice world, and as also does the exotic wildlife, which cannot be experienced anywhere else except in zoos (or on TV). Tink for a moment, for example, about the amazing migrations of the elephant seal, which can dive to several hundred meters (up to 2,500 f) to feed, while slowing its heartbeat. Why should anyone care about that? Well, if you are a climate scientist, you can stick a little device onto the animal’s head to record water temperature with depth in places it would be impossible to monitor by ship or other means. Tat’s a plus for understanding how the world works. Does it hurt the animal? No, it falls of when the animal molts every year. How useful is the data? Tis book explains.
It is becoming clear that we humans are now so abundant that we are acting like a geological force on the surface of the planet, changing the air, the oceans, the ice, and the plant and animal life. Our efects are rapid. Our largest efects have come about since World War II, creating such a break with the climate and biodiversity of the recent geological past (which geologists call the Holocene Epoch of the past 11,700 years), that the geological community is now considering naming the period since 1950 as a new geological time period, the Anthropocene Epoch, which currently represents one human generation, but will continue. Tat does not mean that all of the relatively recent temperature rise, ice melt, and sea level rise have taken place in the Anthropocene. For example, there is good evidence for sea level having started to rise very slowly perhaps as long ago as 200 years, and Alpine glaciers began their modern retreat around 1860. However, temperature rise has accelerated since 1970 along with sea level rise, so a great deal of global overheating and its consequences have taken place since 1950—within the Anthropocene. Is there really a link to how much carbon dioxide our fossil fuel burning has put into the atmosphere? Yes—more than 90% of all the coal, oil, and natural gas ever burned by humans has been burned in my lifetime, since 1950.
To explore these and many other questions about what ice means for life on our planet (including human life), these pages will take you on a journey to the world’s main icy places, many of which I have visited in the course of a long career as a geologist, geochemist, and oceanographer. Journeys are where we experience diferences from the usual, and learn about other people and places and ourselves; they help our imaginations to grow. I capitalize on my journeys to usher my readers from one scientifc truth to another and from one important question to the next, making sure to highlight the diferences as well as the similarities between the world’s three great icy
regions, the “Tree Poles,” comprising the Arctic, Antarctica, and mountain peaks, whose snow and ice together, you may be surprised to learn, cover one full quarter of the planet. I hope these journeys help you to grow in your appreciation of the vital importance of the Tree Poles, of the rapidity with which their ice and snow is melting, of the dangers that holds for us, no matter where we live, and of the urgency with which we must therefore stop polluting our atmosphere with a blanket of gas that comes from burning coal, oil, and natural gas. Te lives and well-being of our children and grandchildren are at stake here, so we all have an interest in leaving them with a habitable planet. I am sure they would prefer not have to face more wildfres, foods, heatwaves, and hurricanes than we have had to deal with.
Along the way we will meet numerous polar explorers and many of the ordinary scientists doing extraordinary work to tease out the secrets of how Earth’s complex climate system works. I name them because it is important for us all to be reminded that it is people on the front line who ferret out the facts that we need, and doing that in the world’s icy places is very expensive, far from easy, and—at the poles—almost impossible in the six months of the year when darkness descends. Tese people are heroes. I salute the work of this far-fung and mostly youthful community. Finally, I am happy to see that, as time has gone by during my 50-year career in science, more and more of these hard-working scientifc contributors are women. I highlight some on the dedication page. May their numbers continue to grow.
I will end with a perceptive quote from the astronomer Carl Sagan:
Our talent, while imperfect, to foresee the future consequences of our present actions and to change our course appropriately is a hallmark of the human species and one of the chief reasons for our success over the past million years. Our future depends entirely on how quickly and how broadly we can refine this talent. We should plan for and cherish our fragile world as we do our children and our grandchildren; there will be no other place for them to live.3
At the time, Sagan was referring to the prospect of a global nuclear winter caused by atomic warfare. But he and his colleagues were making it clear that “the human power to alter the habitability of our planet marked a fundamental shif in our role on Earth—one that we [still have] not yet integrated into the institutions wielding that power.”4
If we do the right things, there is still hope. And afer all, we are responsible for the way things are; we did it, so we should fx it. By doing so, we may be able to save Earth’s refrigerator, or what’s lef of it. Enjoy the ride.
Acknowledgments
Science is a collective enterprise—aside from our individual eforts we build on what’s gone before, and collaborate with those with complementary expertise to build our pictures and stories of what is going on in the felds of our interest to fnd out how the world works. I am immensely grateful to an enormous number of people who have helped me throughout my varied 50-year career in science to expand my knowledge and understanding of how the Earth’s climate system works. Tere are far too many to thank them all individually in these few pages; indeed the list would go as far back as my chemistry and geography teachers in grammar school, who without knowing it set me on the path that led me to a PhD in geochemistry.
I am also grateful to the large number of people whose names I never knew, but who questioned me in depth afer my many public lectures on climate change. Tey showed me what people’s concerns were, and alerted me to the need for a popular educational book about the role of ice in the climate system. Teir questions reminded me that very few people indeed have any acquaintance other than via a TV set of what the world’s icy places are like, because all that TV sets do is provide you with a picture, not an experience of reality. Te reality is hard, as I discovered for myself during several visits to the Arctic, the Antarctic, and the high mountains.
I am especially grateful to the ofcers of SCAR (the Scientifc Committee on Antarctic Research), who appointed me to be their frst executive director, and especially to Professor Jörn Tiede (now deceased), the SCAR president at the time, who arranged for me to gain frsthand experience of Antarctic science through an inspection of the research stations in Dronning Maud Land in the southern summer of 2004. I am most grateful, too, for the advice and the company of Hartwig (Hardy) Gernandt, who showed me around down there. Settling in to my new job was made much easier than it might otherwise have been thanks to the help of Peter Clarkson, the former secretary of SCAR, who remains a good friend and who is always willing to provide advice on Antarctic matters. Rosemary Nash, whom I hired as the SCAR secretary, proved to be a most able assistant, and someone on whom I could rely 100% to help me to get the job done.
I have made a great many friends throughout the SCAR organization, all of them more than willing to provide me with wise advice. It seems almost invidious to single any of them out, but I would like to express my gratitude in particular to Jeronimo Lopez-Martinez, Chuck Kennicutt, Stephen Chown, John Turner, Hong-kum Lee, Dongmin Jin, Peter Clarkson, the late David Walton, Peter Barrett, Eric Wolf, Jane Francis, Chris Rapley, Daniella Liggett, Phil Woodworth, Paul Mayewski, and Martin Siegert, not forgetting my trusty ofce assistants, Marzena Kaczmarska, Michael Sparrow, and Renuka Badhe. It’s also been a pleasure to talk about ice and climate
Acknowledgments
with experts like Robin Bell, Heinz Wanner, Valérie Masson-Delmotte, and Bob Binschadler.
Peter Barrett kindly agreed to read and comment on every chapter, and I was given sound advice by: Peter Clarkson on the Antarctic (Chapters 3 and 5); Phil Woodworth on sea level (Chapter 8); Volker Rachold on the Arctic (Chapter 6); Joel Summerhayes and Monica Insoll on economics (Epilogue): and Eelco Rohling on my frst and fnal chapters—but all the errors are mine. Paul Mayewski and Will Stefen kindly reviewed my manuscript.
Chris Scotese, Mark Serreze, and Andre Berger kindly provided particular fgures, Kieran Baxter kindly provided photographs, and Dame Jane Francis kindly provided access to the map-making facilities of the British Antarctic Survey.
My SCAR ofce was based, as all previous ones have been, within Cambridge University’s prestigious Scott Polar Research Institute (SPRI), and I am most grateful to its director, Julian Dowdeswell, for housing us there, for providing me with wise advice on polar matters, and, on my retirement from SCAR in 2010, for making me an emeritus associate of the Institute and thus enabling me to continue my climate change research. I also much appreciated being able to interface with the SPRI staf, who provided me with much assistance and advice over the years.
I also thank my fellows on the team who managed the International Polar Year 2007–2008, for furthering my education on the science of ice and snow at both poles, and especially cochair Ian Allison for his friendship and encouragement, and Olaf Orheim for facilitating my interactions with Norway. I would not wish to forget my German colleague, Volker Rachold, who worked closely with me to bind SCAR together with the International Arctic Science Committee to address bi-polar science issues. We made an exceptionally good team.
My gratitude also goes to Kim Crosbie, former executive director of the International Association of Antarctic Tour Operators (IAATO), who introduced me to the travel company Abercrombie & Kent, with whom I spent fve splendid cruise seasons along the Antarctic Peninsula as a shipboard lecturer. I greatly appreciated the assistance of Bob Simpson and Julia Evanof in facilitating my trips south, the education in Antarctic wildlife that I got aboard ship from Larry Hobbs, Charlie Wheatley, Marco Favero, Patri Silva, Jim McClintock, and Rich Pagen, and the history lessons in polar exploration from Bob Burton (now sadly deceased).
In recent years I have had the good fortune to have been invited to provide advice on how the science of ice melt and sea level rise bears on the proposed new geological time period, the Anthropocene. Tank you for that Jan Zalasiewicz. Apart from my work with Jan, I have especially benefted from a close association on the Anthropocene Working Group with Will Stefen, Colin Waters, Jaia Syvitski, and Mark Williams.
I much appreciated assistance from the editorial team at Oxford University Press, especially Jeremy Lewis.
Acknowledgments
A special thanks is reserved for the late Ian Jamieson, who planned our glacierhunting expeditions to the Alps.
Last but never least, I am as ever grateful for the support and understanding of my long-sufering wife, Diana, who put up with me staying bent over my keyboard while I tapped out my thoughts on climatic matters, immersed in my own little world.
1 Introduction
July 2021 was the world’s hottest month ever recorded, 0.92°C (1.68°F) above the 20th Century average of 15.8°C (60.4°F).
National Oceanic and Atmospheric Administration (NOAA), August 13, 2021, https://www.noaa.gov/news/its-oficialjuly-2021-was-earths-hottest-month-on-record
At sustained warming levels between 2°C and 3°C, there is limited evidence that the Greenland and West Antarctic Ice Sheets will be lost almost completely and irreversibly over multiple millennia; both the probability of their complete loss and the rate of mass loss increases with higher surface temperatures. At sustained warming levels between 3°C and 5°C, near-complete loss of the Greenland Ice Sheet and complete loss of the West Antarctic Ice Sheet is projected to occur irreversibly over multiple millennia; with substantial parts or all of Wilkes Subglacial Basin in East Antarctica lost over multiple millennia.
IPCC, 2021 (in press): Technical summary. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press (ipcc.ch)
The rate of ice sheet loss increased by a factor of four between 1992–1999 and 2010–2019.
IPCC, 2021 (in press): Summary for policymakers. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press (ipcc.ch)
Ice—The Canary in the Coal Mine
Ice is the canary in the coal mine. When our planet’s ice starts melting year-on-year, we know we’re in trouble, for two reasons. First, ice is a wonderful refector of solar energy. Tat property helps to keep our overall planetary temperature in a range suitable for life “as we know it.” Lose the ice and we lose that protection. Second, when land ice melts, the sea level rises, putting at risk our coastal populations and our great port cities, the hubs for the global trade on which we have all come to depend. Te stability of the world’s ice, then, is an extremely important part of our life-support system, impacting global temperature, the water cycle (foods, droughts, fres, and water supplies), and the sustainability and habitability of the coastal environment where 10% of the world’s population lives and works.
Yet, for most of us, permanent ice is out of sight and out of mind, at the poles or at the tops of high mountains. Except seasonally, when those of us in temperate zones might see some winter snow and ice, the most ice that we are likely to see is when we go—usually on long journeys—to winter ski resorts, and not many of us do that. Tese days most people live in cities, they are no longer closely connected to the land as populations once were. Having lost their moorings in nature, they are unaware both of the climate change that is occurring and of its implications. For the most part only those who are immersed in nature, like gardeners, farmers, fshermen, backpackers, or climbers have the high level of ecological awareness to appreciate the dire ramifcations of global warming and ice loss for our species. And it would appear that for many people, “out of sight, out of mind” translates easily into “don’t care.”
Most ice loss is happening in places that don’t create news. If shrinking glaciers were common in the populous areas of California or Great Britain, it would be on the front page. As a result, unless they are skiers, skaters, or ice hockey players, most people’s acquaintance with ice today comes from using ice in our drinks or watching reruns of the flm Titanic. But had we lived in the 19th century, and even as late as the 1920s, we might well have cooled our food in an “ice-box” with ice imported from somewhere cold. Transporting ice for ice-boxes was quite a sizable industry before modern refrigerators were developed in the 1920s and became widespread thanks to the development of refrigerants and the increasing availability of electricity. We just don’t appreciate today how lucky we are, and what a boon refrigeration has been to global levels of human health. But even that is now seen to have a dark side—a byproduct of the early refrigerants was the creation of the ozone hole over Antarctica.
Exploration of icy places has gripped our imaginations, not least as the bodies of past animals and even people have emerged from their icy graves. Mammoths and other large mammals that were entombed by ice during the last glacial maximum some 20,000 years ago are sufciently well preserved to tell us a lot about past conditions in the tundra. And the discovery in 1991 of the body of Ötzi the Iceman in a melting Alpine glacier provided insights into the clothing and diet of c.3,200 years ago.
In the following pages I will take you to the worlds icy places to see what is happening to ice, snow, and permanently frozen ground (or permafrost). Along the way we will explore what the passing of our permanent ice will mean for the futures of our ofspring—yours and mine alike. In efect, our icy places act as the world’s refrigerator, helping to keep our climate relatively cool. If we are not careful we will lose that refrigerator, with unimaginable consequences.
I will illustrate my narrative with tales from my own visits to the world’s icy places, where I have been both for work and pleasure. Tis will not be a dry tale of the science of change. Tese environments are quite magical in their own right, and I have taken the time to shine a light on some of the wonders I have seen along the way, as well as the efects of change on wildlife. Exploring these far-of realms has challenged our hardiest and boldest explorers, and my tale will introduce you to some of their exploits and discoveries. I hope you will fnd the ride illuminating, and that it gives you a new “taste” for ice.
One thing I hope you will learn is that ice cores from the polar regions have given us detailed and compelling records of climate change, providing us with an 800,000year-long baseline against which to assess to what extent the climate changes that we are seeing now are remarkable or just the climate system doing its thing. As Paul Mayewski of the University of Maine says, ice cores are “ice chronicles.”1 He sees the climate history from ice cores as helping to locate us in time, in much the same way that space exploration helps to locate us in space. Tese new technologies (ice coring and space exploration) provide us with new views of our place in the universe. We can now go even further and supplement the 800,000-year-long perspective, which has only been available since 2006, with geological records of climate change that go far back beyond that baseline, although in less detail, helping us to fnd near analogues in the past for what we are seeing today. Te past provides us with a window into the future.
A key question we will address in this book is—to what extent is what we see today a refection of “normal” change, especially in the polar regions, and to what extent is it to do with our accelerating human activities? Te people who will help us along our way are the scientists studying the workings of the climate system, past, present, and future. Most of them work on the front lines of scientifc exploration either in universities, or in government laboratories devoted to the same ends.
Let’s Talk about Ice
Ice is amazing stuf. If you hit it with a hammer it behaves like a rock and shatters into splinters. But it also fows, like a thick viscous fuid, under the infuence of gravity. Te ice sheets on the very top of Greenland and Antarctica are very slowly fowing under
their own weight down toward and then out across the ocean. Can other rocks fow? Yes, molten rock fows—most of us have seen lava fows on the screen if not in reality. Solid rock can also fow under the extreme heat and pressure deep in the Earth. You can see the result in the contorted strata uplifed in mountains. Buried down deep, the heated strata become malleable enough to bend into enormous folds before being uplifed into mountain ranges that are then eroded to display their innards to the passing traveler. But while “normal” rock doesn’t fow at surface temperature and pressure, ice does. Why? Because at temperatures of around 0°C ice is very close to its melting point, which makes it weak and easy to deform. Over time it can slowly spread out sideways under its own weight, which helps it to form continental-scale ice sheets.
Ice also erodes as it fows. It’s not the ice that does the cutting. Rock breaks apart when water within tiny cracks expands to form ice. Ice transports fragments of rock torn from the beds of ice sheets and glaciers. Tose fragments in turn act like coarse sandpaper, gouging the rocks over which they pass and wearing them away to carve vast U-shaped valleys and deep troughs that when fooded by the sea form the fords common to coastlines north and south of about latitude 50° in places like Norway, New Zealand, Alaska, and Chile.
Ice has a liquid counterpart: it is, afer all, nothing more nor less than solid water. But, unlike other rocks, ice foats on its fuid counterpart. It’s the only common substance to do that. Chunks of basalt will sink into a lava lake, but solid water foats on its liquid parent. Tis is because when water freezes its volume expands, giving its solid form a lower density than its liquid form: ice has a density of 917.4 kilograms (kg)/m3 in freshwater, while the density of pure water is 1,000 kg/m3 (which was the basis for the defnition of the kilogram). Te density of ice increases to1,025 kg/m3 in seawater, but seawater is denser than freshwater, so the ice still foats. Te diference in density between water and ice in the sea “is about 10% . . . [which] is why 10% of the mass of an ice foe or an iceberg protrudes above the sea surface.”2
Ice has another fascinating property that is crucial for our understanding of how the climate changes, as Peter Wadhams explains.2 You have to supply a lot of heat to melt ice (which explains why it takes so long for the ice in your drink to melt). Te heat you need to melt a kilogram of ice when it has reached its melting point is known as its latent heat of fusion, which is 80 calories per gram. Now, given that a calorie is the amount of heat needed to raise the temperature of 1 gram of water by 1°C, then if you need 1,000 calories (1 kcal) to melt 1 kg of water, you will need 80 kcal to melt the same amount of ice. Tat amount would heat the same mass of water to 80°C.
To cut a long story short, this means that as long as sea ice remains in the Arctic it will keep the air temperature in contact with the ice, and the water immediately below the ice to 0°C. In efect the ice is acting as an air conditioner, one which because of global warming is about to break down. In the form of snow, ice has another important property. When it blankets the ground or the sea ice it acts as a great insulator, maintaining sea ice and permafrost throughout the summer melt season in the coldest regions.
Ice also has a gaseous counterpart—water vapor—which makes up on average about 4% of the atmosphere, although in some places (as above deserts) there is almost none. Under the right (very dry) atmospheric conditions, ice has a very strange property: it can convert directly into water vapor by a process known as sublimation, known to occur in certain rare environments in Antarctica.
Our planet’s climate system is delicately balanced near the point where all three phases of water can exist: solid, liquid, and vapor. And compared with the other planets, we have a lot of liquid water, which covers 72% of the planet’s surface as ocean, to an average depth of about 3,700 m (12,154 f). As the famous astronomer and science popularizer Carl Sagan once said—Earth is the Blue Planet. Seen from distant space we appear as a “pale blue dot.”
So, with all that water, and masses of land, surely ice shouldn’t be much of a problem? You could be forgiven for thinking that was true, if you lived on the plains more or less anywhere between the 50th parallels of latitude, because our great masses of ice lie mostly north or south of the 60th parallels, except on the tops of mountains. To understand the importance of ice in our climate system we need to know what area it covers, because that governs how much solar energy ice’s white surface refects back to space, helping to keep the planet cooler than it would be without any ice.
It would be easy to tell ourselves that with 72% of Earth’s surface covered by ocean we need only concern ourselves with ice on land, the remaining 28% of the planet’s surface. If only that were true. But much of the surface of the polar seas freezes in winter and becomes covered by sea ice. Taking Antarctica and the Arctic together, the average amount of the global ocean covered by their sea ice amounts to about 20% of the total in any one year, which amounts to roughly 14.5% of the global surface area. What about ice on the land surface? Surface ice covers 10% of the land to depths of more than 2.5 miles (4 km) in places in Antarctica and close to the same in Greenland. Beyond the area of surface ice lies an area of permanently frozen ground, or permafrost, covering 20% of the land surface locally to depths of up to more than 1.25 miles (2 km) in places, but usually less, and mostly in the Northern Hemisphere.
Covering much of the world in winter, also especially in the Northern Hemisphere, is snow, which can cover up to 30% of the land surface, although, unlike permafrost or surface ice, snow is not permanent. But let’s not forget that snowfakes are ice crystals—in efect snow is just another form of ice, and, as snow deposits thicken, their bases eventually do compress into solid ice. It would not be unreasonable to assume that between them, ice, permafrost, and snow cover up to 40% of the global land surface throughout the year. Tat’s 11.2% of the global surface area.
Adding all this up, the combined area of sea ice, plus land ice, plus snow and permafrost amounts to roughly 25% of the surface of the planet. Tat may be hard to get your head around if you live between the 50th parallels of latitude, where there’s no permanent ice or permafrost and hardly any snow. And those fgures overlook the fact that much of the drowned ground beneath the continental shelf in the polar regions is permafrost—permanently frozen ground. Tis formed when sea levels were
lower by perhaps as much as 130 m (427 f) during the Pleistocene Ice Age of the past 2.6 million years (see Chapter 8 for an update on sea level lowering).
When the sea level began to rise 20,000 years ago afer the Last Glacial Maximum, the continental shelves were fooded, trapping that permafrost beneath a cover of cold polar water. In modern times a thin active layer of permafrost melts at the surface every summer. Below it are much thicker layers mixed in with ice (for example old frozen ponds) which never melt (or have not until now).
We can make a rough calculation about how much ice, snow, and permafrost expanded during peak Ice Age cooling, by considering the change in albedo (Earth’s refectivity). Today it is about 0.30 (that is, 30% of incoming solar energy is refected by Earth’s snow, ice, and deserts). However, calculations suggest that during the Last Glacial Maximum, the albedo increased to about 0.32.3 Hence the coverage of the Earth in ice, snow, and permafrost may have increased from some 25% today to closer to 30% at that time.
Such a change would have come about because much of North America north of Kansas City was covered by the Laurentian Ice Sheet, with permafrost and snowy tundra further south. Scandinavia and most of Britain and northwest Europe north of the latitude of London and Berlin were also under ice, as was much of Eastern Siberia, with snowy tundra and permafrost further south. Land ice spread over the exposed continental shelves around the Arctic Ocean, and covered the continental shelf around Antarctica. Sea ice extended south from the Arctic to close to northern Scotland, while in the south it extended a good 10 degrees of latitude north of its present northern limit around Antarctica.
While the expansion in the area of ice, snow, and permafrost may have only been an extra 5% or so, its volume expanded considerably, with the new ice sheets of the north reaching much the same thickness as the Antarctic Ice Sheet—up to nearly 3 miles (5 km). Probably the best expression of the enormous increase in ice volume during the glacial maxima of the last Ice Age comes from the global fall in sea level, which may have reached –130m (427 f), exposing most of the world’s continental shelves to the atmosphere. Tis would have been a very diferent-looking planet.
With modern global warming, some of the water fooding those polar continental shelves in the Arctic is becoming warm enough to stimulate the decomposition of the organic remains trapped in drowned permafrost. Researchers have come across bubbles of methane (CH4) streaming up through the Arctic Ocean to add to the growing load of greenhouse gases in the air. Fortunately, this process is not rapid, nowhere near as rapid as the melting of the shallow permafrost on land in the Arctic. As yet, however, scientists are not sure of the extent to which the melting of the upper layers of the permafrost on land or beneath the sea will contribute either carbon dioxide (CO2), or methane (CH4) to the atmosphere.
Decomposition under oxidizing conditions produces CO2, while under reducing conditions it produces CH4. Both are greenhouse gases, although CH4 is thought to be 28 times more efective than CO2. Te diference between the two is that CH4 is unstable in the atmosphere and will disappear within around 12 years unless it is
continually replaced, whereas CO2, being stable, has an extremely long residence time in air of many thousands of years. Methane is also only present in tiny amounts— parts per billion (ppb) by volume, while CO2 is present in parts per million (ppm) by volume.
Submarine permafrost is not the last part of the story of our planet’s ice. Deep within the oceans, on the continental slopes that border our shallow continental shelves, the coldness of the water and the pressure of its mass create conditions for ice to form within the sediments on the ocean foor. As this deep ocean ice forms in the sedimentary pore waters, in a zone between 200 m (656 f) and 1,500 m (4,923 f) or more below the seabed, it traps gas from decaying organic matter. Most of that gas is CH4, commonly known as “marsh gas” because it is produced in ponds and lakes by the decomposition of rotting organic remains in the absence of oxygen.
Te CH4 produced by decomposing organic matter in deep ocean sediments becomes trapped within cages of ice to form structures known as gas hydrates, or clathrates, which occupy pore spaces and can also form layers within the sediments. We can detect these hydrates by sound, using seismic surveys, and sample them through deep-ocean drilling. Tey cover much of the world’s continental margins at water depths greater than about 400 m (1,313 f). Tat gives us a lot more ice on the planet.
For our purposes, we may be able to largely ignore that ice as relevant to the story of global warming, since most of it is so far removed from the Earth’s surface that many thousands of years of warming of the deep ocean would be required before it melted. Nevertheless, in 2009, over the continental slope west of Svalbard, Graham Westbrook and colleagues found numerous plumes of CH4 rising through the water column from near the top of the gas hydrate stability zone.4 Since these plumes originated from the continental slope they cannot have originated from permafrost formed on the continental shelf when it was exposed during times of lowered sea level; they must have come from destabilized CH4 hydrates. In a few places, Arctic researchers have also found CH4 bubbling up to the surface over fractured subseabed reservoirs of natural gas (fossil fuel) on the continental shelf.
So, here we are on a planet one-quarter of which is covered by ice in one form or another. Tere has been a lot more ice on the planet in quite recent times, geologically speaking. For the past 2.6 million years of what geologists call Pleistocene time, Earth has been passing through an Ice Age during which there have been periodic expansions and contractions of polar ice in both hemispheres, as we shall see in later chapters. Te amount of ice has fuctuated with time in response to a beat driven by regular changes in the Earth’s orbit. We’ll deal with that topic in more detail later.
In between the Ice Age maxima, the planet lived through what geologists refer to as “interglacial” periods that were as warm as or a bit warmer than conditions have been for the past 11,700 years, an interglacial period termed by geologists the Holocene.
Te relatively warm and stable climate of the Holocene was ideal for the spread of agriculture and civilization.
In the chapters that follow we will explore the history of our changing climate and ice, starting in Chapter 2 with the long geological history of ice on our planet. We will discover that for much of geological time Earth’s climate has been in a warm “greenhouse state,” with average global temperatures between about 21°C (70°F) and 31°C (88°F). But at particular times, and for particular reasons our climate has descended into a cold “icehouse state,” featuring extensive ice. Te most recent of these icy times began when a great ice sheet formed on Antarctica 34 million years ago. Conditions continued cooling to the point that by 2.6 million years ago extensive ice sheets covered much of northern Europe, Siberia, and North America.
We will see that the patterns of changing climate through time refect multiple interacting infuences including: the changing infuence of continental positions; the gradual increase in the output of energy from the Sun over time; the development of life, with plants using CO2 to grow; exhalations of gases like CO2 from volcanoes; the chemical weathering of rising mountains, with the decomposition of silicate minerals by acidic rain sucking CO2 out of the air; the burial of carbonate skeletal remains on the deep sea foor, acting as a carbon sink; regular changes in the Earth’s orbit and the tilt of the Earth’s axis; changes in the Earth’s albedo with the growth or decay of ice and snowfelds; and sunspot cycles, which change very slightly the amount of energy Earth receives from the Sun on short to medium timescales.
Over considerable periods of geological time, some of the CO2 that was in the atmosphere and became transferred to the ocean becomes trapped on the seabed in deposits of calcium carbonate or organic carbon. In deep water the carbonate deposits are mainly the skeletons of marine creatures, but in shallow water they may form either coral reefs or, in some places, like the Bahama Banks, chemical precipitates in the form of tiny egg-shaped structures known to geologists as “ooids.” When clustered together, carbonate ooids make up a particular form of limestone known as an oolite.
Organic matter—the remains of the sof parts of organisms—usually forms a tiny component of marine sediments, but may accumulate in large amounts when bottom waters contain little or no oxygen. Such conditions prevail today for example in the depths of the Black Sea, on the continental shelf of Namibia, and on the continental slope of Peru. Tese organic-rich deposits form more or less permanent traps for what was once atmospheric CO2.
When deeply buried and “cooked” by rising heat from the Earth’s interior, organicrich sedimentary deposits can form the source rocks for oil and gas. On land we fnd similar carbon traps today in deposits of peat. In some past geological periods, conditions in certain places where the climate was humid and forests abounded, led to vast amounts of organic matter accumulating in deposits that we now know as coal. Tese extremely slow processes of carbon entrapment played an important role in the variation of atmospheric CO2 on geological timescales.
How confdent can we be in our understanding of past climate change? Reconstructing past climate is the work of paleoclimatologists. Like much of geology, of which it is a subdiscipline, paleoclimatology is a bit like putting together a jigsaw puzzle in which many of the pieces are missing and, as Henry Pollack puts it, “there is no picture on the box to guide you.”5 Like Henry, I am among other things a paleoclimatologist, and have produced my own guide to the subject.6
Paleoclimatologists study the annual layers in ice cores and their equivalents in marine sediments on the seabed or uplifed onto land by mountain building. We examine the annual climatic changes represented by tree rings, the growth rings in corals, or the layers in stalactites from caves. Layers of dust and salt concentrations in ice cores can give us crude indications of wind strength and direction, while layers of ash can tell us about the timing of far-fung volcanic eruptions.
When it comes to more recent times, we can use things like agricultural records of harvest times for crops or grapes, for example, to tell us about annual change. We also have access to public records of humidity and temperature, although most of these don’t date back further than about 1600 ce. Records of the poleward migrations of animals, plants, and insects tell us about the efects of warming on life. Fishing feets, whalers, and navies kept records in their log books of waves, weather, and even the location and front of the pack ice through time. For generations, people have been measuring the temperature of lakes, the dates of snowfall and melt, the dates at which lake and river ice forms and melts, and—from boreholes—the changing temperature of the subsurface of the Earth.
Tanks to satellites, we now have vast numbers of measurements of the shrinking lengths of glaciers. Tide gauges around coasts have routinely measured sea level, measurements that are now supplemented over the global ocean by lasers on satellites. Tese kinds of records have helped us to document climate change through the ages and the relation of those changes to ice. Records of such changes have been most limited from Antarctica, where the frst weather station was not established until 1903, in the South Orkney Islands, by the Scottish National Antarctic Expedition; it is now managed by Argentina.
Today the weather is measured at thousands of places around the world and across the oceans, many of the measurements being made by automated devices including ocean buoys. Autonomous foats and gliders as well as strings of instruments deployed through the water column measure the temperature and salinity of the ocean’s subsurface. Satellites measure atmospheric and oceanic temperatures, the properties of the surface of land, ocean, and ice, and the height of the sea’s surface. Balloon-borne devices measure temperature profles up through the atmosphere.
It is the amalgamation of these multiple and growing data sets that provides the raw material that tells us that the world is warming and allows us to compare what is happening now with what happened in the past. Combining these data from scattered sites with numerical models enables us to map climate change today and in the past, and to project into the future how the climate and ice may change, for example
