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A Scenario That Will Rock Your World.

An address to Australian Taxation Office executives


28 June 2004


“At the moment, we are an ignorant species, flummoxed by the puzzles of who we are, where we came from, and what we are for. It is a gamble to bet on science for moving ahead, but it is, in my view, the only game in town.”

-         Lewis Thomas (1979)

“The stories scientists tell us are not simply bedtime tales. They place us in the world, and they can force us to alter the way we think and what we do.”

-         Thomas Levenson (1989)

“One of the most shocking scientific realizations of all time has slowly been dawning on us: the earth’s climate does great flip-flops every few thousand years, and with breathtaking speed.”

- William Calvin (2002)

 Introduction: Big History     

Everything we think of as ‘world history’ has occurred in the past five thousand years. Very few of us have anything like a clear grasp even of that time frame. This evening, I invite you to consider a radically longer time frame - the time frame of natural history. In particular, I want to draw your attention to a couple of extraordinary characteristics of natural history, which put our own history in a very different context from how we usually think about it.

            In his path-breaking study of the origins of vision, 530 million years ago, Australian biologist Andrew Parker remarked, in 2003: “We think of ancient history as perhaps a couple of thousand years ago. Ten thousand years would be extremely difficult to conceptualise, a hundred thousand, let alone a million, inconceivable. So hundreds of millions of years of evolution are way beyond the realms of the most vivid human imagination.” Yet it is tens and hundreds of thousands, even many millions of years I want you to ponder: the kind of time frame that David Christian, in his marvelous new geo-history, Maps of Time, calls ‘big history’

            These vistas of time have only been opened up, by geologists and palaeontologists, over the past 170 years, going back to the work of Charles Lyell in the 1830s and Charles Darwin in the 1850s. The really extended understanding of the age of the earth and the evolution of life on it has only been done in the past half century, however, since the general acceptance of the theory of plate tectonics in the 1960s and punctuated equilibrium in the 1970s. But it is very recent investigations into ancient climates on which I want to focus your attention. The breakthroughs there have occurred only in the past ten to twenty years; indeed, mostly in the last five.

            There has, of course, been much debate in recent years about greenhouse warming and the possibility that our species is overheating the planet. But it is not anthropogenic overheating that I want to talk to you about. It is the long term patterns of climate change which antedate our kind and which have only in very recent years started to become clear to specialists. Those patterns take an especially significant and startling form over the past million years and I shall, shortly, zero in even more narrowly on the last 20,000 years - the years coinciding with the historic rise of our species. But first, let me illustrate the very long term patterns.

The Earth’s Climate: From the Hadean to the Holocene.

            Here is a graph of the earth’s climate since the planet was formed 4.6 billion years ago. It is a slightly modified version of a graph in David Christian's Big History (p. 132), as are the next few graphs. The long period from the planet’s formation through the Pre-Cambrian was hot, but cooling. It is not to scale. The part to note most specifically is the last billion years, in which there is a roller-coaster of cooling and warming, with average global temperatures oscillating between about 26 degrees and 12 degrees Celsius. Below 14 degrees, you get glaciation. You will observe that there have been long periods of glaciation and long eras of warmth - greenhouse eras.


            Now, look at a much shorter time period - the last 600 million years. Here are all the great geological epochs during which there have been complex life forms on earth, punctuated by a series of mass extinctions. The best known of these, indeed the only one that could be said to have penetrated popular culture, is the end Cretaceous mass extinction, in which the dinosaurs disappeared from the face of the earth. The thing to observe here, however, is the wavy line graphing average global temperatures. You can see that it rises to greenhouse levels three times and drops below the glaciation line twice.

            What you cannot see in detail in either of these graphs is the trend during the Tertiary and Quaternary epochs, the last sixty five million years, during which apes and hominids evolved. Here it is:



What is plainly observable here is the general downward trend in average global temperatures from 24 to 15 degrees, - that is to say, a marked cooling of the world’s climate, since the end of the Cretaceous. This is the epoch of the mammals. Hominids, of which we are the only remaining kind, appear only in the Pliocene, which is to say the last ten million years and especially in its last phase, the Pleistocene, starting two million years ago. But looking at this graph, you cannot discern what has been happening in that period in any detail.

            Let’s look, therefore, at the Pleistocene:


Now we start to cut to the chase. You will see, at a glance, that what looked before to be a smooth curve is actually a very bumpy one, when viewed in detail. Indeed, the closer you get to the present, the bumpier it gets. With the mean temperature hovering around 15 degrees, but the glaciation point being 14 degrees, the planet has been slipping into and out of ice ages for over a million years, with more and sharper fluctuations in the most recent half million.

            These fluctuations were unknown until a few decades ago, but it has been ascertained that they coincide with and are likely caused by variations in the earth’s orbital cycle around the sun and perturbations in the axis of its rotation. Over a period of 100,000 years, the earth’s orbit around the sun shifts from roughly round to markedly elliptical. Every 41,000 years, the tilt of the earth’s rotational axis shifts through an arc of perhaps 2 degrees and every 19,000 to 23,000 years there is a wobbling of the earth on it axis, which causes the time when the earth is closest to the sun to shift from northern summer to southern summer.

            These are known as Milankovitch Cycles, after a Yugoslavian mathematician who predicted them, based on his knowledge of the solar system, decades before they were actually detected. So, the bumpy line in the Pleistocene registers the Milankovitch Cycles, as they impacted earth while the climate was slowly cooling for other reasons. This is the epoch of the ice ages and it has played a profound role in the biological evolution of our species. What it shows is that long ice ages, lasting around 90,000 years, have been interspersed with relatively short inter-glacial ages, lasting around 10,000 years.

            So, against this deep background, I invite you to consider a fundamental reality, which had entirely escaped our species until very, very recently. Everything we think of as world history, from the beginnings of agriculture to the beginnings of space exploration, has taken place in an inter-glacial age, which has already lasted about 15,000 years; far longer than inter-glacials normally last. The ice ages are not over and when the ice returns, many of those zones in which our huge populations and intensive agricultures exist will be frozen over, as they have been again and again over the past two and a half million years.

The Dansgaard-Oeschger Cycle.

            That, surely, is food for thought. It is not the end of the matter, though. For during the last couple of decades, oceanographers and geochemists have been investigating yet another pattern of climate fluctuations, which takes place alongside the larger pattern of glacials and inter-glacials. This is a pattern called the Dansgaard-Oeschger or D-O Cycle, named after Willi Dansgaard and Hans Oeschger, who did much of the pioneering work on it, in the 1980s. It consists of frequent, very rapid climate flips, centering in the North Atlantic, which have drastically altered global climate every few thousand years, on average, throughout the Pleistocene.

            Here is a graph of the D-O Cycle over the past million years.

You will notice that this graph starts from the right hand side, not the left, so that the far left represents the present. The line is extremely jagged and every spike in it represents a D-O event, that is to say, a climate flip of varying degrees of severity, in which the climate of Europe changes suddenly, from warm and wet to cool and dry, with corresponding changes elsewhere; for example, massive droughts in Africa and eastern Eurasia.

            The high points on the chart, of which there are ten or a dozen, are the inter-glacials. Each is followed, as you can see, by a sharp cooling and a long descent into glaciation. The relatively extended inter-glacial labeled on the graph is the one before our own, known to climate scientists in Europe as the Eemian. It lasted for around 13,000 years. Let me pause, at this point, to remark that it is, surely, completely extraordinary that human scientific endeavor has been able to reconstruct this climate record. It is one of the countless wonders of modern science and it should fill us with awe. I invite you, just for a moment, to reflect on the staggering achievement that all these graphs represent.

            Now we come to the graph that I want to imprint most firmly in your memories and imaginations:


 This graph moves from left to right, unlike the preceding one. It covers just the last 20,000 years. This is our time. I began by stating that all of what we usually think of as ‘world history’ has occurred in the last five thousand years - the millennia since writing was invented. Those five thousand years are covered by the extreme right hand column in the graph. It is, for the moment, the columns to its left that I want you to look at closely.

            The leftmost column shows the last millennia of the most recent ice age. Around 14,000 years ago, there is a very sharp upturn, followed by a jagged descent and then a deep, cold trough, from about 12,700 years ago until about 11,400 years ago. This cold trough is known as the Younger Dryas. It was a climate flip that tossed a Europe which had begun to emerge from glaciation, back into the freezer for some 1,300 years. Then, with equally startling suddenness, the climate flipped again and things warmed up dramatically. What had happened? A standard D-O event. It changed Europe’s climate from something like its current condition to Siberian conditions within a decade; then, 1,300 years later, it flipped back again.

            Think about that. There has been nothing remotely like this in historic time. If the same thing was to happen now, the consequences for human civilization would be all but unimaginable. And here’s the thing: the fact that more than 11,000 years have passed since this last major D-O is anomalous, in the context of what we can see in the longer term patterns throughout the Pleistocene. We do not know why things have remained warm for so long and we have no reason to believe that the long term pattern has changed in any fundamental way.

            As a measure of how disastrous a major climate flip would be, consider that, 8,200 years ago, there was a much smaller and briefer cooling. It is marked on the chart. This downturn lasted about a century, but it caused major perturbations and would have a catastrophic impact were something like it to recur in the 21st century. You can gain some dim appreciation of the scale of impacts I am talking about here, simply by looking at the even smaller bumps in the rightward half of the graph and considering that the little peak labeled ‘Medieval Warm Period’ made it possible for the Vikings to settle Greenland, but, when it passed, they were driven out by the cold.

How Credible is the Abrupt Climate Change Hypothesis?.

            If you’re like me, you will be pretty stunned by all this. I want, therefore, to show you that this is not some crazy or irresponsible fantasy, invented by some crackpot. It is credible and we should take it seriously. I came across the concept of abrupt climate change for the first time in a book called A Brain For All Seasons, by William Calvin, which I’d bought because of my interest in the evolution of the human mind. In that book, Calvin advanced the thesis that our brains, our mental abilities, evolved as they did, over the past two million years or so, largely in order to cope with the challenges posed by climate flips.


            Calvin is a neurophysiologist, not a climate scientist, but his account of the case was so compelling that it quickened my interest in climate change in a way that public debates about greenhouse gas emissions and global warming had never done. I began, therefore, to look into the science of climate change, if only to see whether his account of the matter could be relied upon. What I discovered was so fascinating, not to say unsettling, that it quite transformed the way I think about the natural world. That is why I was so keen to share the matter with you this evening.

            Here is Calvin’s own account of how he first learned of the matter of abrupt climate change, from Swiss geophysicist Hans Oeschger, twenty years ago:

“…it was long suspected that orbital factors weren’t the whole story, as the southern hemisphere ice sheets melted back at the same time as the northern ones. Why should ice sheets in the Andes and New Zealand melt when the closest approach bonus was in their winter time? They should have been out of phase with the northern one, but they were in phase, synchronized by something.

The other thing that made climate scientists suspect that it wasn’t so simple was a wild flower, white with a yellow centre, of the rose family, called Dryas octopetala. It is cold adapted and is found on the tundra - not among shrubs and pine trees. Well, a century ago, Dryas pollen turned up in cores of a lake bed in Denmark, above a layer of trees, at a depth now dated back to about 12,000 years. A return to cold made no sense then, according to the Milankovitch orbital view…There should have been pine seeds in those cores, not the pollen of a tundra flower…

…But the pros knew about such anomalies as the Younger Dryas and…the Greenland [ice] cores were starting to show some puzzling results, as the Danish researcher Willi Dansgaard and his colleagues reported, in 1982. I first heard of the abruptness, per se, in 1984, when the Swiss geophysicist Hans Oeschger gave a talk in Seattle. The time calibration on one of his slides prompted me to ask him afterward about just how quickly temperature had changed.

Oh, he said, the big drop took just a few years. The enormity of such a whiplash caused me to assume that we were having some language difficulties and so I persisted, asking ‘Just a few decades?’ No, no, he replied, merely a few years..” (Calvin, 2002, pp. 215-17)

In short, Calvin has not made up any of the story about abrupt climate change. He has learned it from those most closely engaged in doing the research. Twenty years on from that encounter with Oeschger, Calvin himself gave a talk at Westminster College, Salt Lake City, in March this year, called ‘When Climate Staggers: Civilization’s Vulnerability to Sudden Change’.

            In those intervening two decades, the work on abrupt climate change has been carried forward by scientists at numerous research institutes across the world. Prominent among them have been the Lamont-Doherty Earth Observatory and the Woods Hole Oceanographic Institution, both at Columbia University. The doyen of the Lamont-Doherty team, which numbers some 200 scientists, is Wallace Smith Broecker. He was awarded the National Medal of Science in 1996 for his work and the Tyler Prize for Environmental Science Achievement in 2002, along with Liu Tungsheng of the Chinese Academy of Sciences, a fellow pioneer in the study of palaeoclimate.

            Broecker’s articles and those of many other specialists on the subject of abrupt climate change, have appeared in the major scientific journals, Science, Nature, Scientific American, Paleooceanography, Quaternary Research, Earth Sciences Review and Oceanography. But until just a very few years ago, the message was simply not reaching the general educated public, or even the wider scientific community. It was Calvin who broke the ice, as it were, with an essay in The Atlantic Monthly, in 1997, called ‘The Great Climate Flip-Flop’.

He wrote that piece, he says, because “it was a scandal that it had gone largely unreported for ten years, despite all the news-feature stories in Science and Nature.” (Calvin 2002, p. 299).

The appearance of Calvin’s essay in The Atlantic Monthly in 1997, coincided with the publication in Science (Vol. 278, No. 5343, pp. 1582-87) of a major paper by Wallace Broecker, titled ‘Thermohaline Circulation, the Achilles Heel of Our Climate System: Will Man-Made CO2 Upset the Current Balance?’ I shall come back to that essay, because it bears on a central bone of contention in current discussions of climate change scenarios - to wit, will anthropogenic global warming actually trigger a D-O event?

As some of you will be aware, this specific scenario is the subject of the Hollywood disaster movie, The Day After Tomorrow, currently screening in cinemas around the world. Hollywood, unfortunately, has made an egregious mess of the matter. The movie makers just could not resist making absurd claims and constructing a melodramatic, politically correct plot. Taken together, these make for a film that is annoyingly bad. But I’ll come back to that. Let me, first, finish what I was saying about the scientific credibility of the basic picture.

            While Broecker’s articles kept appearing in the serious journals, Richard B. Alley, Evan Pugh Professor of Geosciences at Pennsylvania State University, followed William Calvin’s lead, by writing a full length book about abrupt climate change, for a general readership. It is called The Two Mile Time Machine: Ice Cores, Abrupt Climate Change and Our Future and was published by Princeton University Press in 2000. It won the 2001 Phi Beta Kappa Award in Science and I recommend it to any of you who would like to read more deeply into the subject.

          Alley went on to chair a committee under the auspices of the National Academy of Science, in the United States, which produced a full length report in 2002, called Abrupt Climate Change: Inevitable Surprises. Based on this report, Bob Gagosian, director of the Woods Hole Oceanographic Institution,

delivered a presentation to the Davos Forum, in January 2003, under the title ‘Abrupt Climate Change: Should We Be Worried?’ I want to quote his opening remarks to you, because they underscore the seriousness with which this matter is viewed at the highest levels of the scientific research community.

            Gagosian told the Davos Forum:

“Most of the studies and debates on potential climate change, along with its ecological and economic impacts, have focused on the ongoing buildup of industrial greenhouse gases in the atmosphere and a gradual increase in global temperatures. This line of thinking, however, fails to consider another potentially disruptive climate scenario. It ignores recent and rapidly advancing evidence that Earth’s climate repeatedly has shifted abruptly and dramatically, in the past and is capable of doing so in the future…

…This new paradigm of abrupt climate change has been well established over the last decade by research of ocean, earth and atmosphere scientists at many institutions worldwide. But the concept remains little known and scarcely appreciated in the wider community of scientists, economists, policy makers and business leaders. Thus, world leaders may be planning for climate scenarios of global warming that are opposite to what might actually occur.”

 He added:

“It is important to clarify that we are not contemplating a situation of either abrupt cooling or warming. Rather, abrupt regional cooling and gradual global warming can unfold simultaneously. Indeed, greenhouse warming is a destabilizing factor that makes abrupt climate change more probable.”

As he explained and as is set out in greater detail in the NAS report, the interaction could occur because abrupt climate change is a non-linear event, which occurs when the climate system crosses a certain threshold - and global warming could force it across the best documented such threshold in the climate system.

            That threshold operates in what Broecker, in the 1997 article I referred to earlier, described as the Achilles Heel of the climate system. As he explained, the world’s oceans run on a sort of conveyor belt, which carries warm waters from the tropics to cooler regions and cooler waters back. In the unique case of the Atlantic Ocean, the warm current, known as the Gulf Stream, carries an enormous amount of tropical warmth to higher latitudes, greatly moderating the otherwise cold climate of northern Europe. He went on to write:

“The record contained in ice and sediment indicates that this current has not run steadily [throughout the Pleistocene] but [has] jumped from one mode of operation to another. The changes in climate associated with these jumps have now been shown to be large, abrupt and global. Although the exact linkages that promote such climate changes have yet to be discovered, a case can be made that their roots must lie in the ocean’s large-scale thermohaline circulation…Variations in the conditions governing the density of high latitude surface waters can lead to abrupt reorganizations of the ocean’s circulation. The surprise revealed to us by the climatic record is the extent, rapidity and magnitude of these atmospheric changes.”

Broecker believed that the most common trigger for one of these non-linear switches was the sudden release into the North Atlantic of large quantities of fresh water, coincident with what is called a Heinrich event - the bursting of a huge natural lake or dam or the breaking off of a massive ice sheet from Greenland or the Hudson Bay area. His concern, as you will probably have guessed, is that global warming could bring about a Heinrich event and thereby force the thermohaline system across the threshold to a D-O event.

          What drives this vast conveyor that Broecker is talking about? The answer, interestingly, is salt. Bob Gagosian explained the mechanism in very clear and simple terms at Davos. This is what he said:

“For a variety of reasons, North Atlantic waters are relatively salty compared with other parts of the world ocean. Salty water is denser than fresh water. Cold water is denser than warm water. When the warm, salty waters of the North Atlantic release heat to the atmosphere, they become colder and begin to sink.

In the seas that ring the northern fringe of the Atlantic - the Labrador, Irminger and Greenland Seas - the ocean releases large amounts of heat to the atmosphere and then a great volume of cold, salty water sinks to the abyss. This water flows slowly, at great depths, into the South Atlantic and eventually throughout the world’s oceans.

Thus, the North Atlantic is the source of the deep limb of the Ocean Conveyor. The plunge of this great mass of cold, salty water propels the global ocean’s conveyor-like circulation system. It also helps draw warm, salty tropical surface waters northward to replace the sinking waters. This process is called ‘thermohaline circulation’, from the Greek words ‘thermos’ (heat) and ‘halos’ (salt).

If cold, salty North Atlantic waters did not sink, a primary force driving ocean circulation could slacken and cease. Existing currents could weaken or be redirected. The resulting reorganization of the ocean’s circulation would reconfigure Earth’s climate patterns.”

As Gagosian already knew, when he delivered this speech, a leading article in Nature, in April 2002, had pointed out that the subpolar seas bordering on the North Atlantic have, in fact, become noticeably less salty over the past forty years and especially in the past decade.


In other words, the available evidence suggests that we could be somewhere in the vicinity of the threshold for a non-linear climate flip. We simply don’t know enough to be sure. Nor do we know how close you can get to such a threshold and still be able to do anything to pull back.

Hollywood and the Nature of the Danger.

            Having written an essay on abrupt climate change last August, before I was even aware Roland Emmerich’s Hollywood film about the matter was in the works, I was intrigued when it was released. I went to see it with an old school friend. We were profoundly disappointed with it. It seemed designed to entertain or scare children, but was wholly lacking in both scientific and social realism.

            The film opens by drawing attention to ocean monitoring in the North Atlantic Seas. Good, I thought, they’ve done their basic homework. Unhappily, it is pretty much all down hill from there. The film has things happen on a scale and at a speed which are totally unrealistic. Whether this makes good cinema is moot, but it is such bad science that it can only confuse a general audience which needs to be soberly enlightened.

            The film has almost the whole northern hemisphere freeze over within days or weeks. This is flatly impossible. The process takes many years to reach a threshold of the kind I have described and, once the threshold has been crossed, a few years to a decade to radically change the climate. Isn’t this dramatic enough for Hollywood? Why make things ridiculous?

The film has temperatures in the continental United States dropping by tens of degrees in seconds, as a huge hurricane sweeps in from the Arctic at minus 150 degrees Fahrenheit. But hurricanes cannot develop in the cold. They are tropical phenomena. And the coldest temperature ever recorded on earth, at Vostok, in Antarctica, is minus 128.6 degrees Fahrenheit. One could go on, but there is little point.

            The social implausibility of the film is equally egregious. Once the full impact of the catastrophe has hit, the film has the United States government evacuate tens of millions of people in a safe and orderly fashion within days, to what Tom Lehrer once called ‘that magic and romantic land south of the border, sunny Mexico.’ Inexplicably, they all wind up in well constructed refugee camps and everyone seems to be behaving at their best, as the US president goes on global television - itself somehow undisturbed by the icing over of most of the northern hemisphere - and confesses that we were wrong to think we could go on releasing greenhouse gases into the atmosphere without upsetting nature’s delicate equilibrium.

            As they say in that part of the States the film ices, “Puh-leez!” Such abuses of both science and common sense made the film a tempting target for climate change skeptics. One of the best known of these is Bjorn Lomborg: 

director of Copenhagen Consensus and of Denmark’s national Environmental Assessment Institute. Lomborg became a global figure in 2001, with the publication by Cambridge University Press of his best selling book, The Skeptical Environmentalist. On 27 May this year, as the Emmerich film opened in cinemas here, he had an opinion piece in The Australian headed ‘Entertaining discredited ideas of a climatic catastrophe’.

            Lomborg wrote in response not only to the film, but to a report prepared late last year for the Pentagon’s Office of Net Estimates, in which abrupt climate change within the next two decades was described as a scenario for which the American government needed to be prepared. He wrote that the scenario outlined in the Pentagon study had been “thoroughly debunked” by reviewers in Science and Nature and that halting the Gulf Stream would be impossible, so that “it is safe to say that global warming will not lead to a new ice age.”

            I was fascinated by these claims, since it is precisely Science and Nature that have published most of the scientific research showing that abrupt climate change could occur and that the pattern of such changes in the past is linked to recurrent halting of the Gulf Stream. Have the specialists abruptly changed their minds? I wondered. I went looking for the reviews Lomborg alludes to, eager to learn what had happened. To my amazement, I could not find any such thing in either magazine.

            I emailed Lomborg and his colleagues in Copenagen, asking could they point me to the reviews in question, since I had been unable to find them. I got no response. I emailed  Bob Gagosian, in New York, asking had he come across anything matching this description and showing that the work of Wally Broecker and so many others had been “thoroughly debunked”. He informed me that he has not, as of last week, come across any such thing.

            Now, I don’t want to give you the impression that I think Lomborg is as unreliable as Roland Emmerich. Lomborg and his colleagues have done a lot of work to rethink the state of the global environment and have challenged quite a number of widespread fears and assumptions about environmental deterioration or man-made environmental damage. I respect that work.

I went looking for the reviews and the debunking he referred to just because I do take him seriously and am open to the possibility that somehow Wally Broecker and his many colleagues have gotten the matter wrong. I have gone to considerable lengths this evening to show you the nature of their reasoning, because I fear that too many people will pick up on remarks such as Lomborg’s and dismiss the science of abrupt climate change, along with the Hollywood film. That, I believe, would be a serious error.

Lomborg had a perfectly rational aim in writing what he did, though he may have unintentionally misread what scientists are saying on the subject. He wrote, “The problem is that if we overestimate the risk that climate change poses, then we will pay less attention to the other challenges facing humanity…Because we cannot do everything, we need sound reasoning and high quality information to defeat the hysteria of Hollywood.”

He is certainly correct in saying that we should rationally seek to determine where to allocate our priorities and resources, given the range of challenges we face. He is also correct to call for sound reasoning and high quality information, as against the hysteria of Hollywood. Where he seems to me to miss the boat is in asserting that the abrupt climate change scenario has been “thoroughly debunked”, i.e. that it is based on hysteria and not on sound reasoning, or high quality information.

There is nothing hysterical about Wally Broecker or Bob Gagosian or Richard Alley or William Calvin. Nor is there any reason that I am aware of for seeing their reasoning abilities or published work as being inferior to those of Bjorn Lomborg. In ridiculing the Emmerich film, Lomborg was knocking down a straw man. By not naming the authors of the articles in Science or Nature that supposedly “thoroughly debunked” the Pentagon scenario, or supplying their dates, he made it frustratingly difficult to check his claims.

By not acknowledging the enormous amount of reputable scientific work that has gone into developing our understanding of abrupt climate change, he left himself open to the counter claim that he is merely ignorant of the matter. Had he wanted to tackle the case at a serious level, he would have done better to have critically evaluated the claims made by William Calvin, in his March 2004 Adamson Lecture at Westminster College, or Bob Gagosian’s January 2003 address to the Davos Forum. Let me, at least, indicate how this might be done, before concluding my remarks.

Circumspection and Critical Analysis.

            In his Adamson Lecture, Calvin was at pains to make clear that we have only in the past decade or so learned that abrupt climate change occurs at all. His use of the pronoun ‘we’ is generous, for of course the overwhelming majority of human beings have not the foggiest idea about all this. What he poses is the question, how do we come to terms with what we have been learning in this regard?

            What has been pieced together about climate history indicates that the Earth’s climate is bimodal. It oscillates between ice ages and inter-glacials on a long sinusoidal curve (the Milankovitch Cycles), but along that same curve it oscillates at much higher frequency and with abrupt switches between warm/wet and cool/dry modes (the Dansgaard/Oeschger Cycle), which appear to be causally linked to periodic irruptions of fresh water into the sub-arctic seas of the North Atlantic (Heinrich events).

            These abrupt shifts are such that they would allow almost no reaction time for a complex system such as human civilization. This is the real thrust of Calvin’s lecture, as it was of the Pentagon’s scenario paper. When the last D-O, the Younger Dryas, occurred, human beings were few, non-agricultural and relatively mobile. That had been the case all the way back through such shifts across the Pleistocene. Now, however, we number billions, overwhelmingly dependent on complex farming, energy, transport and governance systems.

            Calvin points out that, under Younger Dryas conditions, Europe would become, within a few years to a decade, like Canada or Siberia. Canada supports 28 million people, Siberia about 8 million. Europe currently supports 650 million, overwhelmingly because of the temperate climate it enjoys. His challenge to his audience was to consider the possibility that, in Europe alone, the onset of a D-O flip could cause the death of at least 600 million people, by cold, starvation, disease and chaotic violence, within a decade. And there would be no recovery, for the climate would remain cool and dry, in all probability, for centuries.

            Why this was not dramatic enough for Roland Emmerich and the Hollywood movie moguls is completely beyond me. But what is it rational to think, or say, or do, in response to such a dire scenario? To reject it out of hand? I suggest not. To panic and throw up our hands? I think not. To assume it to be a sure prediction and call for revolutionary changes to our civilization? I suggest not. What, then? To summon the mental discipline required to examine it closely, test the assumptions and the reasoning involved, identify where we need to know more, then model various possible ways of heading off, or preparing for variations on the scenario.

            It is surely worth recalling, in this context, that we have seen at least two comparable long term scenarios over the past 150 years, in which initial data sets and projections turned out to be erroneous or inadequate in a number of ways. The first was the left-wing analysis of industrial capitalism, most famously that by Karl Marx:

which described it as bound to produce growing immiseration of the working classes and consequent radical revolution, following which a command economy would provide freedom and plenty for all people. I do not need to remind this audience, I am sure, how thoroughly debunked this scenario now stands.

           The second was the over-population model, most famously developed by Paul Erhlich, at Stanford University, according to which an exploding human population would cause a breakdown of industrial and technological civilization in the late twentieth century, with resources being used up, agriculture failing and hundreds of millions of people dying in gigantic famines. The Club of Rome took up the cry, as did many others. Just a generation on, never having seen the collapse predicted by Erhlich, we are seeing very different demographic trends emerging globally, even the possibility, in mid-century, of a kind of population implosion. This is the context in which Bjorn Lomborg and others have been urging that we rethink how we think about environmental challenges.

            If, therefore, we were to respond to the abrupt climate change scenario with uncritical alarm or calls for poorly thought through social and economic upheavals, we would quite possibly be turning ourselves into latter day Leninists or population bombers, if you’ll pardon the expression in present geopolitical circumstances. This would ill serve us. Rather, we need to remain, if I may put it thus, very cool headed. We need, as it were, to chill out and make as certain as possible that we are both understanding the past correctly and weighing the variables in future scenarios scrupulously.

Concluding Remarks: Consilience and Resilence.

            The changes in the human world over the past century or two have been breathtaking, by any measure. The advances in our knowledge of natural phenomena and of our own past, the developments in our technologies and methods of inquiry have been truly staggering. What we have just learned about long term patterns of climate change belongs in this context. So, I suggest, does the fact that most of us suffer from a chronic inability to take it all in, to make integrated sense of the world.

            More than most things you might read about, though, I think the possibility of abrupt climate change ought to rock your world. We occasionally talk about thinking outside the box, or outside the square. Well, this scenario really is outside the square, as far as most of our comfortable and long-settled assumptions are concerned. That, more than the calamitous possibilities Calvin points to, are what make it so thought-provoking, in my opinion.

I want, therefore, to conclude with just a few remarks about thinking outside the square and the kind of thinking that the abrupt climate change hypothesis entails. For, you see, all of us, as professionals and as inference-drawing, meaning-making human beings, are faced daily by having to assimilate information of various kinds. For the most part, we do so by screening out what does not compute and interpreting the rest in terms of what we already take to be the case. How else could we operate? Yet, every so often, we encounter information that does not compute in terms of our existing assumptions, but is not easily screened out. That’s when there is an opportunity for deeper thinking.

Such deeper thinking occurs when we recognize the incompatibility of what we have encountered with what we already believe and set about making explicit what is at stake, and why and then determining whether we should alter our beliefs. In simple, everyday ways, you might say, we do this all the time. What I’m talking about here, though, is the sort of case in which something quite fundamental confronts us; something which we cannot deal with easily, or on the run.

This requires taking quite deliberate steps to re-examine the way we are thinking about the issue in question. That is strenuous work and does not come naturally. Nor are we equipped to do it just any day of the week, as it were. We don’t know how to do it, for the most part. We cannot readily see what specific things it would be best to rethink. We encounter resistance, not only in ourselves and our own habits of thought, but in the prejudices of those around us and in institutionalized practices rooted in the very assumptions that we might seek to challenge.

Peter Senge made the term ‘learning organization’ current, but what challenges of the most fundamental kind require is pro-active thinking organizations - organizations that do not simply learn rapidly when they encounter challenges, but seek actively to anticipate challenges and to build resilience into their systems and practices, awareness and flexibility into their most fundamental, governing assumptions. You only have to contemplate the world of religion and politics to realize that these things are devilishly difficult to achieve, much less maintain. Yet they are what the world we have created for ourselves increasingly demands.

William Calvin concluded his address, in March, by observing that we would do well to begin pro-actively exploring how we can build much greater resilience into the physical and infrastructural underpinnings of our civilization, with a view to surviving future climate shifts; even abrupt and massive ones. Such an ambitious technological and social project could only proceed on the basis of cognitive habits and practices of critical thinking and rational dispute resolution which are decidedly lacking at present. Yet the idea is bracing and I, for one, would much sooner embrace that challenge than settle for either complacency or hysteria.

We live in extraordinary times. Both for better and for worse, the possibilities that loom before us are awesome. We have looked this evening at a possibility of catastrophe on a scale that beggars both belief and imagination. But simultaneously, we can see possibilities of technological breakthroughs and even social renovation of quite stunning kinds. How can we reconcile all these things? Keep our balance? Avoid both panic and irrational exuberance?

Your responses to those questions will vary. Let me, however, offer a single word as a kind of Ariadne’s thread that might guide you through the labyrinth. The word is consilience. The biologist Edward O. Wilson uses it to describe a new inter-disciplinary integration of what we know and how we think. He called for the development of “fluency across the boundaries” between the humanities and natural sciences that would “provide a clear view of the world as it really is.” There is a task for a whole new generation of Renaissance scholars!

I see the history of climate and the scientific analyses of climate change as a way into this integrated view of the world and our place in it. For this history  - big history, in David Christian’s terminology - puts us and our pretensions in deep perspective and shows us our world natural and whole. It shows us how very narrow all human myths and ideologies have been up until now and draws us into a future with a vast horizon.

The possibility of abrupt climate change should wonderfully concentrate our minds. For it tells us that our future is anything but assured and that our modern assumptions about endless material progress and boundless growth may rest on more fragile foundations than anyone had ever realized. That, I suggest, is salutary, since we are all too prone to complacency and arrogance. It challenges us to rethink our worldviews and beliefs about the future, starting from a whole new level of awareness about the deep past. It challenges us to think and think again and keep thinking about the day after tomorrow.