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Local epidemics"| Regional epidemics Pandemics

Local epidemics"| Regional epidemics Pandemics

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13.1. Intervals of low CO2 concentrations in Antarctic ice cores correlate (within dating uncertainties) with major pandemics that decimated populations in Eurasia and the Americas.

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13.1. Intervals of low CO2 concentrations in Antarctic ice cores correlate (within dating uncertainties) with major pandemics that decimated populations in Eurasia and the Americas.

numbers for Eurasia come from McEvedy and Jones's Atlas of World Population History. In my opinion, the correlation between pandemics, population losses, and dips in CO2 minima looked suggestive enough to be worth pursuing.

The historical record of disease began when a pestilence of unknown origin struck Athens in 430 bc, decimating the Athenian army during the Peloponnesian

War with Sparta. Outbreaks of what may have been malaria occurred in Italy in AD 79 and 125 (the latter called the plague of Orosius). Malaria is not usually fatal today, but these outbreaks killed large numbers of people, perhaps because natural resistance to it had not yet developed. The disease hit especially hard in the countryside, and many farms went out of cultivation as farmers moved into the cities. Still, these outbreaks seem to have been relatively local in scale. A somewhat more extended outbreak, apparently of smallpox, the Antonine Plague, struck the Roman Empire between 160 and 189, killing the Roman emperor Marcus Aurelius. At its peak, some 2,000 people died each day. The symptoms (fever, skin eruptions, and inflammation of the mouth and throat) match those of smallpox. Mortality rates were high enough that farmers were drafted to fill the depleted ranks of the Roman army.

The year 251 saw a renewed pestilence called the plague of Cyprian after one of its early victims. The type of disease is again uncertain, but smallpox and bubonic plague are among the more likely choices. Whatever its origin, it was lethal and lasted for 16 years, becoming nearly pandemic from Egypt to Scotland. Anecdotal information from some regions indicates more deaths than survivors in the wake of this pestilence, with large areas of farmland in Italy reverting to the wild. Once again, people fled from the countryside to the cities, where they may have been more vulnerable. Recurrent outbreaks of bubonic plague continued in the Roman Empire for three centuries, and some (but by no means all) historians infer that the Roman Empire began to be seriously weakened by this ongoing loss of population.

Some historians also claim that the extended sequence of pestilence between the first and fourth centuries ad contributed to the growth of Christianity. As many people grew ill and died, the terrified survivors would have found little consolation in the jealous infighting of the older Roman gods. By contrast, Christianity offered the hope of miracles in this life (healing of the sick and casting out of spirits) and the promise of life after death. As conversions to Christianity accelerated during the plagues, it moved from an outlawed religion of martyrs to the official religion of the empire by the end of the fourth century.

But the pestilence continued during Christian times, culminating in 540-542 with a plague of unprecedented intensity named after Justinian, emperor at that time and destined to be the last of the line. This pandemic, almost certainly bubonic plague, was first recorded in Egypt, swept north into Palestine, Greece, and then the Black Sea and Constantinople, by that time the center of authority for the remnants of the empire. It then moved through the cities of North Africa along the Mediterranean coast and into southern and western Europe. It generally arrived first at coastal seaports and then spread into the interior cities and countryside. Because its lethal effects were felt on several continents, this plague was the first great pandemic.

Most of the plague during this era was probably carried by fleas hitching rides on rats. The fleas bit humans and transmitted the disease, which began with a fever, followed by large swellings (buboes) in the groin or armpits, and then a coma. Any physical movement on the part of those afflicted caused excruciating pain. Shortly after death, black spots appeared on the body. In one sense, at least, bubonic plague had a merciful side: death came quickly, usually within a week. At the height of the plague of Justinian, 5,000 to 10,000 people died each day in Constantinople, too many to be buried by the survivors. Their rotting bodies, filling the cities with the stench of death, were dumped into the empty towers of forts or loaded onto ships that were set adrift on the ocean. This time, not just villages and towns but even some cities ceased to exist, as the social order largely collapsed, and agriculture almost entirely ceased in many regions. Some 25% of the population may have died in this one outbreak.

Lesser but still extremely severe outbreaks of bubonic plague continued in Europe at intervals of 10 to 20 years until ad 590. The reason for the roughly decade-long spacing of outbreaks may be that most survivors had a natural resistance to the disease, and so the plague briefly abated for lack of available victims. After 15 or 20 years passed, many members of the newest generation lacked immunity, and plague would flare up anew. Some 40 percent of the population of Mediterranean Europe may have died in the cumulative outbreaks by 590 (fig. 13.1). For some countries, these losses were not replaced for four or five centuries.

For unknown reasons, the disease began to abate in Europe after 590, with regional epidemics recorded for the next 150 years, even though nearly continuous outbreaks of plague continued to afflict the Muslim-dominated Middle East between 627 and 717. After an outbreak in 746-748, bubonic plague disappeared for some 600 years.

The long Roman-era interval of epidemics that culminated in a major pandemic matches fairly closely the first extended CO2 minimum in the ice-core record (fig. 13.1). The subsequent plague-free interval from 749 to the middle 1300s also correlates reasonably well with the rebound of the CO2 trend (given the dating uncertainties in the latter), and of European and Chinese populations, to higher values. At least at a glance, it seems plausible that pandemics, populations, and CO2 levels may have been linked during this interval.

Another devastating plague pandemic struck in the late 1340s. Originating perhaps in Central Asia, it reached the Near East by 1347 and swept across Europe from the Black Sea to the British Isles and into North Africa by the early 1350s. This plague was transmitted not just by fleas and rats, but also by pneumonic bacilli spread by coughing, sneezing, kissing, and even just breathing. Of an estimated 75 million people living in Europe just before the plague hit, at least 25 million, or one out of three, died within a few years.

Once again, farms, small villages, and even entire towns were abandoned, their inhabitants having died or fled to the cities. Crops again lay unharvested in the fields, and vineyards untended. As before, the cities provided no refuge, with mortality rates as high as 70 percent in the hardest-hit areas, although some regions were spared. Bodies of people from lower-class families were dragged out into the streets and left to rot, and few dared come to funerals held for the wealthy. The Pope was forced to consecrate the Rhone River near the city of Avignon so that bodies dumped there could be said to have received a Christian burial. Ships that had lost their entire crews to plague drifted aimlessly across the Mediterranean and North seas.

Some historians believe that the Black Death changed the feudal structure of medieval England, and perhaps elsewhere. Prior to the plague, poor serfs worked the land of their lords without much hope of improvement in their position. But after plague killed so many people, the resulting shortage of farm workers gave the survivors some bargaining power. For the first time, laborers moved around the countryside looking for higher wages and better situations. A form of tenant farming took hold—not complete freedom, but better than serfdom.

This first plague pandemic was followed by several more virulent outbreaks through the 1390s. By then, an estimated 40-45 percent of the population may have been killed in many parts of Europe. Entire villages simply disappeared, some forever. The impact of these plagues lingers today in phrases we use without giving their origin any thought: "avoiding someone like the plague"; a problem that "plagues us"; or "wishing a plague upon someone."

I find it difficult to imagine the horror of a disease that suddenly arrives from unknown sources by unknown means, kills an average of one out of three of your family members and your neighbors in a year or two, and then abates, at the point when you had begun to give up hope of surviving. Even more cruelly, by the time you have finally begun to feel safe and perhaps guardedly hopeful, the disease returns 15 or 20 years later and claims still another generation of victims. The Black Death pandemic and subsequent plague outbreaks through 1400 line up well with a dramatic CO2 decrease in the Taylor Dome ice-core record, although the better-dated ice-core record from Law Dome shows a much less obvious drop (fig. 13.1).

Plague outbreaks continued in Europe for the next 300 years. Some historians refer to the worst of these outbreaks as pandemics, and thousands of people died in London each week at the height of an outbreak in 1665, just one of many during this interval. And by this point in human history, other diseases had also joined the "army of pestilence" in taking a toll on human populations. Influenza (from pigs) became a major problem by the early 1300s. Smallpox (from cattle) became epidemic in Europe in the 1500s and remained a major killer until the

1800s. Regional epidemics of cholera struck India after 1500, with an unusually lethal outbreak in 1543.

Yet this disease-ridden interval in Europe does not seem to rank as a true pandemic. After the Black Death horror of the mid-1300s, European populations rebounded to preplague levels within a remarkable 150 years and continued to grow from the 1400s through the 1800s (fig. 13.1). Mortality rates must have been considerably smaller than during the Roman or medieval eras.

But a third (and worst) preindustrial pandemic was still to come—the one resulting from European entry into the Americas. Europeans carried many diseases to which they had gained a large measure of immunity, but which decimated Native American populations from Canada to Argentina. Some of the diseases were carried on the persons of the Europeans, at that time mostly a flea-infested, lice-ridden people who abhorred bathing as unhealthy. Diseases also arrived on their pigs, cattle, and other livestock. This wave of invading pestilence, unprecedented in history, included smallpox, influenza, viral hepatitis, diphtheria, measles, mumps, typhus, and whooping cough, and somewhat later, scarlet fever, cholera, and bubonic plague. Even diseases such as mumps and measles that sound trivial today were often fatal for people with no natural immunity.

In recent decades, estimates of the size of the pre-Columbian populations in the Americas have soared. Where once historians thought that 10 to 20 million people lived in the Americas, conservative estimates from reputable sources like W. Denevan (The Native Population of the Americas in 1492) are now in the range of 50 to 60 million people, with more extreme proposals exceeding 100 million. The largest populations were the Aztecs in Mexico, the Inca in Peru and Bolivia, and the surprisingly large populations living in the tropical rain forests of Central America and the Amazon Basin. The much larger population estimates for the Amazon in recent years come from new archeological methods such as low-level airplane overflights that trace out road and village patterns or terraced hillside gardens, followed by detailed studies on the ground.

After the Europeans made contact, up to 90 percent of the native populations died. Entire villages that once lined the valleys of the lower Mississippi River system were abandoned, along with endless cornfields in between. After the forests again took over, the only obvious evidence left of the former existence of these agricultural people was massive earthen mounds used for ceremonial purposes. Most of these mounds were plowed by settlers and flattened to create towns and cities. In the Amazon Basin and other rain forest regions, lush tropical vegetation swallowed up most evidence of former habitation. Many decades later, so little evidence remained of the former occupation of North America that scientists and historians in the 1800s and early 1900s assumed that populations had been relatively small. For the few regions (like Cahokia, Illinois) where massive structures indicative of more advanced civilizations survived, scientists and historians discounted the obvious explanation (that they were of Native American origin) and assumed that European people must have created these structures in an earlier era.

Today, the best estimate is that some 50 million people died just from having come into contact with Europeans. This was the greatest pandemic in all of preindustrial history, and, in proportion to the size of the global population, the worst pandemic of all time. Out of roughly 500 million humans then alive on Earth, 50 million (10%) died in the Americas.

The indigenous populations of the Americas never recovered from this great pandemic. Not until large-scale European settlement after 1750 did the total population in the Americas reach the pre-Columbian level. The overall duration of this third great "American Pandemic"—1500-1750—closely matches the third and largest CO2 drop in the Law Dome ice core (fig. 13.1). In this case, the age of the CO2 minimum in the ice core is firm, and its correlation in time with the pandemic is certain.

Since the 1800s, mortality from diseases has been lower than before, with some exceptions. The last recorded epidemic of bubonic plague occurred in southern France and northern Africa in 1720. The near-disappearance of plague during the 1700s is often credited to improved sanitation, but this explanation is disputed by some medical historians who infer that the species of rat that carried plague-bearing fleas was for some reason displaced by a species that did not. Vaccines for bubonic plague became available only in 1884, but a serious outbreak still occurred in 1910 in Manchuria, and isolated cases occur even now. Gradually, improvements in sanitation and new medicines have suppressed the worst forms of many diseases, although AIDS has killed millions of people despite the best modern medical efforts. In any case, the rebound from low CO2 levels after 1750-1800 seems to correlate reasonably well with the reduced incidence of high-mortality disease.

Historians must weigh and balance many contending explanations for the complex array of developments that determine the course of history. Still, the evidence in hand leads me to a clear conclusion: the major CO2 dips in the ice-core records correlate more persuasively with population drops caused by major pandemics than they do with times of war or famine.

It was tempting to conclude that pandemics must be the primary cause of the CO2 drops. But an old adage in science holds that "correlation does not prove causality." Two trends may be wonderfully correlated in time and yet not related in a cause-and-effect sense. It was still possible that the CO2 values and the disease/ population trends were each responding to some other common factor but were not actually linked in a causal sense at all. I still needed to find a specific, plausible causal mechanism that linked CO2 and pandemics.

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