Can you imagine a winter so cold that the sea is frozen over all the way from Norway to Denmark? Not even the last Ice Age saw such a thing, for then the sea level was lower, and all of Scandinavia was joined together by dry land. Yet in 1837-38 the Norwegians survived such a season. And what of having to watch as every day the sea rises another 15 centimetres, until after two years what was your home lies 150 metres below the waves? This may be unimaginable to coastal dwellers today, but it was the fate of a dense population of farmers living 7500 years ago around what is now the Black Sea.
Most humans have thankfully been spared such wild swings of weather and sea level, yet abrupt shifts in the physical environment have been far from rare in recorded history, and even small variations can inconvenience or threaten millions of people. The Long Summer has a fresh approach to the way we think about shifts in climate, both large and small, and how they have affected people. Indeed, Brian Fagan takes the view that climate change has fundamentally shaped the course of civilisation. This is his third book on the topic (his earlier works examined floods and the Little Ice Age) and in it he uses the unprecedented accuracy of newly recovered records of past climates to flesh out his theory. The data Fagan brings to bear on his thesis are in some instances truly remarkable; the record for some regions provides something very close to a year-by-year account of the way the seasons, rainfall and temperature have varied over thousands of years. For the most part, however, the record is far less detailed, and in a few critical instances it’s almost non-existent.
The book’s title refers to the last ten thousand years of Earth history, known as the Holocene Period, which climatologists have often – with some justification – characterised as a period of exceptional warmth and stability. Perhaps in order to give us an idea of what conditions were like before the arrival of this long summer, Fagan begins his analysis in the alien world of the last Ice Age, around eighteen thousand years ago. Then, sea levels were more than 90 metres lower than they are today, and what are now densely populated regions of North America and Europe lay under kilometres of ice. Even areas lying south of the ice, such as central France, were treeless sub-arctic deserts, with a growing season of just eight weeks. It appears from Fagan’s account that Ice Age summers hardly justify the name, for their brief sixty days were an alternation of relentless, freezing northerly winds with a few still days when a stifling haze of glacial dust filled the air.
In comparison with such miserable conditions, the Holocene was, I suppose, some sort of long summer; but the fluctuations documented by Fagan make it clear that it was the kind of summer that can offer four seasons in a single day, all too often creating an unimaginable hell for those forced to endure the extremes. Fagan uncovers enough droughts, snap-freezes and floods during this supposed heyday of balminess to spawn enough famines, plagues and wars to see off half the Earth’s human population. Yet the capacity of such events to disrupt lives forms just one thread of Fagan’s argument, which is developed alongside two innovative hypotheses. ‘Climate,’ he writes on his final page, ‘has helped shape civilisation, but not by being benign.’ In many ways this is a climatic version of ‘what doesn’t kill you makes you stronger’; but it also represents a novel approach, for until now archaeologists have been more inclined to point to the warmth and stability of the Holocene as a key factor in allowing the establishment of cities and empires. His second hypothesis, introduced in the book’s opening pages, involves our increasing vulnerability to climatic events: ‘In our efforts to cushion ourselves against smaller, more frequent climate stresses, we have consistently made ourselves more vulnerable to rare but larger catastrophes. The whole course of civilisation . . . may be seen as a process of trading up on the scale of vulnerability.’ It is in the interplay between these three truly big, and sometimes seemingly contradictory ideas that the tension of Fagan’s work unfolds.
The first thing to understand is how climate change is generated. Our corner of the universe is, in broad terms, relatively stable; yet tiny changes in the solar system can be amplified into monumental changes for particular parts of our planet. Take the slight shift in the Earth’s orbit between 10,000 and 4000 BC, which brought between 7 and 8 per cent more solar radiation to the northern hemisphere. This enhanced the rainfall of Mesopotamia to levels 25 to 30 per cent higher than today’s, and because the rain fell in summer it markedly altered the ratio of rainfall to evaporation, increasing sevenfold the overall moisture available to plants. The impact on the region was prodigious, turning what was once a desert into a verdant plain. After 3800 BC, the Earth’s orbit reverted to its former pattern, reducing the amount of sunlight enjoyed by the northern hemisphere, and rainfall began to deteriorate in Mesopotamia, forcing many farmers to abandon their fields and wander in search of food.
The ancient civilisations of the Near East, and Mesopotamia in particular, are crucial to Fagan’s hypothesis. He suggests that many of the famine-driven wanderers found refuge in a few strategically placed settlements whose location, near where irrigation canals branched off the main rivers, buffered them from the worst of the changes in rainfall. Uruk, in what is today southern Iraq, was one such settlement, and Fagan thinks that many of the starving migrants were put to work there: they received a food ration in exchange for their labour in a multiplicity of construction projects, including the maintenance of irrigation canals. Reduced rainfall, Fagan believes, also forced Uruk’s farmers to innovate and intensify; to use, for the first time, ploughs and draft animals to till fields in a rotation that involved double cropping. With grain production localised around strategic towns, surrounding settlements began to specialise in fishing or in producing goods such as pottery and metals, which were sold at Uruk’s markets for the increasingly scarce grain. Together these changes led to the development of a more centralised authority that supported a new profession – the world’s first bureaucrats – to tally and distribute the vital grain. It all adds up to a fundamental shift in human organisational structure, with the result that by 3100 BC Mesopotamia’s southern cities had become, Fagan says, the world’s first civilisations. The city, he believes, is a key human adaptation to drier climatic conditions.
There is little doubt that the kinds of change Fagan outlines occurred among the cultures of Mesopotamia, or that they represented a key advance for humanity. It also seems to be well established that climate has changed on the Mesopotamian plains along the broad lines that Fagan indicates. But can we be sure that a deteriorating climate was the cause of these shifts? After all, cities such as Uruk may have used their strategic location to grow in size and complexity regardless of what the climate was doing. A detailed record of climate change for Mesopotamia, closely correlated with cultural change, could provide a test of the idea, but Fagan acknowledges that ‘we still lack definitive information on ancient climate changes in southern Mesopotamia,’ in large part because the action of the rivers, as they change course, destroys the sedimentary deposits that might have preserved a record of that kind. Indirect tests are possible, yet Fagan seems strangely indifferent to them. One would be to determine whether historically documented, famine-driven diasporas have generated similar advances in human culture. The great El Niño-induced famine of the late 19th century, which killed between 30 and 50 million people in a region from Sudan to China and sent millions more wandering, is the prime example here, yet frustratingly Fagan leaves its impact unanalysed.
Despite Fagan’s assertion, few of the key innovations that occurred in the ancient world, as humans progressed from being hunter-gatherers to citizens of great cities, can be tied in a detailed way to the climate record. His theory has overtones of older paradigms, in particular the idea that Northern Europe’s great advances were due to its difficult climate, while the cosseted inhabitants of the tropics lacked the stimulus to create truly great civilisations and thus became ripe for colonisation. Jared Diamond’s idea that natural advantage (such as an abundance of domesticable species and a fertile land) rather than climatic challenge explains why certain societies ‘succeed’ in becoming more complex seems to me more likely to be correct.
Looking at the data Fagan presents, I’m inclined to believe that rather than making them stronger, a deteriorating climate usually kills off civilisations, for he documents a great number of societies that have imploded or disintegrated as climate conditions have worsened, while few if any are convincingly demonstrated to have grown more complex. A climate record of unparalleled resolution has been recovered from sediments preserved in Lake Titicaca and the nearby Quelccaya icecap, both of which correlate well with the collapse of the cities of the Tiwanaku Valley. Agriculture was always a risky proposition at some four thousand metres above sea level on the Bolivian Altiplano, where frost, snow and drought all menace. Yet for around six hundred years prior to 1100 AD, fifty thousand people inhabited a spectacular stone city in a region surrounded by fertile fields. Both lake sediments and the icecap reveal that rainfall decreased abruptly around 1100 AD when the higher (and thus potentially drier) fields were abandoned, as was the grand city itself. Rainfall didn’t return to its previous levels until the mid-15th century, by which time the Incas had taken over.
While The Long Summer presents a good deal of fine science in an adroit manner, it contains a number of annoying inaccuracies. Gunung Tambora, for example, is not in east Java, nor is eastern Brazil Bolivia (as an important map on page 239 indicates). Combined with an occasional tendency to gloss complex matters, these minor errors leave larger doubts in the reader’s mind. None of the questionable glosses is central to Fagan’s hypothesis, but some are fascinating nonetheless. Were a mere two hundred drinkers enough to consume the 1150 litres of beer produced daily in the ancient Egyptian city of Nekhen? They would have had to down nearly six litres (ten and a half pints) of beer per person per day, a volume that would surely challenge even contemporary Australians. If there is an explanation for this fascinating statistic, Fagan doesn’t provide it. Yet I’m convinced that he is right to implicate climate change in the collapse of some cultures, and in the light of his second great idea (about the ‘rising vulnerability’ of human civilisations to climate change) this is a very important point.
To many readers, Fagan’s concept of rising human vulnerability may at first seem absurd: food shortages hardly enter into the thinking of most citizens of the developed world, and if they do, most people would assume that by accumulating food surpluses and evolving efficient transport systems, contemporary societies have to some extent ‘drought-proofed’ themselves. Fagan begins his ruminations on the topic by recalling a sleepless night spent aboard a yacht in a Force 9 gale in the Bay of Biscay. As he lay hove to, ‘surviving easily but otherwise helpless’, supertankers smashed effortlessly through the waves on their way south to the Cape of Good Hope. In that stormy region, 25-metre-high waves are not unknown – ‘walls of water so steep and powerful that they have cracked supertanker hulls like eggshells’ – and in such conditions, Fagan tells us, ‘our small boat’s chances would be better than the tanker’s,’ with the massive waves passing ‘underneath us with less effect than these nine-metre ones’. ‘Survival,’ he concludes, ‘is often a matter of scale.’
Most hunter-gatherers, he notes, live in very small-scale societies and at low population densities, and while they feel the effects of minor climatic perturbations they are, like Fagan’s yacht, well equipped to deal with them by moving on in their uncrowded landscapes, or if their primary food source has failed, by switching to less favoured foodstuffs. Having worked with hunter-gatherers in Australasia, I’m not entirely convinced that they are free to wander at will in response to drought, for tribal boundaries are fiercely protected. Yet links with trading partners and distant kin often allowed Australian Aborigines to find refuge in drought, so perhaps the basic premise is correct. Agriculturalists, on the other hand, by virtue of their high population densities and specialised lifestyles, have lost much of this flexibility. ‘We humans are like spiders,’ Fagan says, ‘acting within invisible webs that we have woven.’ And from these, agriculturalists cannot escape, even if they wanted to: their landscapes are too crowded, the secondary foods they might have relied on have often gone, and in any case they lack the complex skills required to live a hunter-gatherer’s life.
Perturbations to two major climate systems seem to have contributed many of the most horrendous swings in climate over the past 10,000 years. One is the Gulf Stream, which can perhaps be characterised as the Achilles’ heel of the ocean’s circulation system. Its flow is a hundred times greater than that of the Amazon, and it brings warm, salty water into the North Atlantic, the influence of which keeps Europe far warmer than it would otherwise be. The Gulf Stream has ceased flowing, or diminished in flow, several times in recent prehistory – most spectacularly perhaps between 11,500 and 10,600 years ago, causing winter temperatures in the Netherlands to plunge regularly below –20 °C and summer temperatures to average just 13° or 14°. It failed again between 8200 and 7800 years ago, and between 4200 and 3900 years ago its flow seems to have greatly diminished. On the two earlier occasions the disruption was caused by vast influxes of fresh water into the North Atlantic: first by the draining of Lake Agassiz (which was centred on Canada’s Lake Winnipeg), whose waters burst through an ice dam separating them from the St Lawrence River; and then by the melting of the remains of the ice dam, again releasing vast amounts of frigid fresh water. The Gulf Stream stops flowing under such conditions because the cold fresh water sits on top of the warm salty water, shutting off the down-welling of the salty water and thus disrupting the worldwide circulation of oceanic water. One very real concern of some of the world’s leading climatologists is that the Gulf Stream may again falter, perhaps as a result of increased rainfall over the North Atlantic, or the melting of the Greenland icecap.
The second great disturber of climatic equilibrium is known as ENSO, the El Niño/ Southern Oscillation. The oscillation results from the sloshing of warm water across the Pacific Ocean. In most years, strong easterly winds blow across the Pacific, causing a build-up of warm surface water on its western shore, around Indonesia and tropical Australia. The warm air can hold a lot of moisture, which brings abundant rainfall to the south-western Pacific. Off the coast of South America, however, the lack of warm surface water allows for the upwelling of cold, nutrient-rich currents. But every few years the winds weaken, allowing the warm water to flow back ‘downhill’ towards South America. Then the anchovies and abundant marine life of the eastern Pacific die, and drought can afflict huge regions of the planet.
Climatologists call the graph tracking the Earth’s rising temperature the ‘hockey stick’, because it has a long handle and a sharply upturned end. The handle represents the relatively stable ‘long summer’ of humanity, the upturned end the sharp rise in temperature predicted to occur over the next hundred years as a result of our emission of greenhouse gases. While the science of predicting rising temperatures from increased greenhouse gases is well understood, predicting what that will do to rainfall and climatic patterns is not easy. One thing that everyone agrees on, however, is that a warmer atmosphere is a more energetic atmosphere, so all sorts of climatic phenomena, from hurricanes to ENSO, can be expected to increase in intensity. If we do nothing to stem our emissions of greenhouse gases, we can expect a rise in global temperatures of up to 6 °C by 2100, making the world warmer than it has been at any time in the last six million years. Fagan says of our present situation:
If we’ve become a supertanker among human societies, it’s an oddly inattentive one. Only a tiny fraction of the people on board are engaged with tending the engines . . . those on the bridge have no charts or weather forecasts and cannot even agree that they are needed . . . Few of those in command believe the gathering clouds have any relation to their fate or are concerned that there are lifeboats for only one in ten passengers. And no one dares to whisper in the helmsman’s ear that he might consider turning the wheel.
The bottom line is that we are all passengers on this ship of fools, whose difficult past should act as a dire warning of what’s to come.
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