Frozen Earth: The Once and Future Story of Ice Ages (35 page)

Other proxies confirm the sunspot observations.
When the sun’s activity is high, the strength of its magnetic field is also high, and cosmic rays (high-energy particles that originate outside the solar system and permeate interstellar space) are deflected away from the Earth in greater numbers than usual.
This happens because cosmic ray particles carry an electric charge, and when electrically charged particles enter a magnetic field, their direction of travel is changed—they curve away from their original path.
Normally, a combination of the sun’s and the Earth’s magnetic fields deflect away most cosmic rays, but some especially energetic ones are only minimally diverted and penetrate through to the atmosphere.
When this happens, they smash into nitrogen and oxygen atoms and make radioactive isotopes such as carbon-14.
The amount of carbon-14 formed is thus a fairly sensitive measure of solar activity—the stronger than normal magnetic field that characterizes times of high solar activity deflects more cosmic ray particles away from the Earth, resulting in lower carbon-14 production.
Tracing how carbon-14 has changed in the atmosphere, which can be done by measuring the isotope in ice cores or tree rings, is therefore another way to gauge the sun’s activity.
The carbon-14 data corroborate the sunspot
record and indicate that solar activity was generally high during the Medieval Warm Period, and low during the Little Ice Age.

As solar activity decreased near the beginning of the Little Ice Age, the signs of a deteriorating climate in the North Atlantic region are abundantly clear both from scattered historical records and archeological evidence.
In the islands of the Canadian arctic, the Inuit people began to migrate south.
By the 1340s, sailors traveling between Iceland and Greenland had to follow longer, more southerly routes in order to avoid ice and treacherous weather.
The Norse settlements in Greenland went into decline and were eventually abandoned as an already unforgiving environment became even harsher.
Skeletons from graves at some of the Greenland settlements show that by 1500, near the end of the settlement period, even the average size of the few people still living there had decreased significantly.
In the worsening weather, farming became increasingly difficult, and their diets correspondingly less varied and nutritious.
In the lowlying coastal areas of Germany, Denmark, and Holland, fierce storms obliterated large tracts of agricultural land in the thirteenth and fourteenth centuries, and by most estimates claimed more than a hundred thousand lives.
And in the Alps, glaciers began to encroach on farms and pastures that had been established during earlier, warmer times.

In spite of these undeniable facts, there is still much debate about the degree to which historical events such as economic decline, famine, the “Black Death” (plague), and changes in political fortune were due to the deteriorating climate as opposed to other factors.
Perhaps climate is just a “forcing factor,” in the same way that the sun’s activity or the Earth’s orbital parameters are forcing factors for climate itself, not wholly responsible, but important enough to tip the balance in one direction or another.
However, some historical events of the Little Ice Age are so widespread throughout Europe that an external factor such as climate seems likely to be the predominant cause.

An example is the disaster that struck across Europe during the early years of the fourteenth century.
The relative prosperity and benign
weather of earlier times had resulted in an expanding population.
Much marginal land had been occupied and farmed.
Then a series of cold, wet years struck.
Grain rotted in the fields, or sometimes couldn’t be planted at all.
The cost of food rose rapidly.
Livestock and people began to succumb to famine and disease, and even the rich had difficulty getting enough to eat.
Social unrest was rampant; gangs of desperately hungry peasants roamed the countryside searching for food, and in some places there were reports of cannibalism.
By the 1320s, land and even whole villages had been abandoned throughout Europe, and population fell precipitously, in places by more than half.
This was indeed abrupt change; it occurred within a human lifetime, at a time when life expectancy was half what it is today.
A few decades later, the first of a series of waves of bubonic plague, the infamous Black Death, hit an already reeling Europe.
Huge segments of the population, especially in crowded urban areas, succumbed to the disease.
The first half of the fourteenth century is also the period that historians identify with the dismantling of the feudal system that had prevailed throughout Europe.
Can all of this be ascribed to climate?
Certainly, the poor harvests of the early 1300s, and the fungus and other diseases that affected crops, can be attributed directly to a series of very wet and generally cold years.
People and livestock, weakened by shortages of food, were especially susceptible to disease.
The Little Ice Age was in its early stages, but already, it seems, it was having a profound effect on society.

The impact of the changing climate was not just felt on land either.
At the time of the Little Ice Age, cod was an important source of protein throughout the North Atlantic region, especially for coastal populations.
Abundant, large, and nutritious, it was in great demand, in part because the Catholic Church allowed its adherents to eat fish, but not red meat, on Fridays.
It was also a permitted food throughout Lent.
It was easily preserved; salted cod is light, has a high food value, and can be kept for long periods without refrigeration.
Long before the Little Ice Age, Norse explorers had carried salt cod as their principal food on sea voyages.
It became an essential and very valuable commodity, and as a result
the cod fishing industry was large and extremely competitive.
As the Little Ice Age began, fish seemed to be there for the taking, not subject to the same season-to-season vagaries of the weather that affected crops and livestock.
But that optimistic outlook was soon to change.

Cod have a limited tolerance for temperatures outside a narrow range of about four to seven degrees Celsius.
Below two degrees they suffer kidney failure.
Because of this, their geographical range, especially at the cold northern extremes, is particularly sensitive to changes in water temperature.
Unfortunately, existing records are not detailed enough to trace exactly how cod populations shifted during the Little Ice Age.
However, several general trends are clear.
As the northernmost Atlantic progressively became ice-filled due to the colder weather, the cod moved south.
Catches around Greenland decreased, as did those near Iceland.
Fishing off the coast of Norway also became more difficult.
The fish didn’t completely disappear from any of these localities, but their numbers dwindled, and it became harder and harder for the Basque, English, and Dutch fishing boats that regularly visited these waters to fill their holds with cod.
As a result, and in spite of the generally stormier weather, they began to search farther afield.
When their explorations first led them to the coast of North America is not known—then as now, fishermen didn’t want to give away their secrets.
But in 1497, the Italian explorer Giovanni Caboto, known to the English as John Cabot, sailed along the eastern coast of Canada and reported waters teeming with cod.
In places, they were abundant enough to literally scoop out of the sea with baskets.
Cabot noted that the sea was also full of Basque fishing boats.
This was only a few years after Christopher Columbus “discovered” North America; the fishermen had certainly been there long before.
Just as the warmth of the Medieval Warm Period had allowed the Vikings to sail westward to North America, so the cod populations, responding to the cold of the Little Ice Age, led Europeans across the Atlantic to the New World.

Although the Little Ice Age was, on average, significantly colder than the immediately preceding and following periods, it was by no
means a single, uninterrupted interval of cold.
There were reprieves, sometimes fairly long ones.
There seem to have been significant spikes upward in temperature in the early 1500s and again in the early 1700s, each followed by a return to much colder times.
There are hints that cod migrations, political crises, and the frequency of famines were all affected by these fluctuations.
In an especially cold period through the mid and late 1600s, cod essentially disappeared from the water around the Faeroe Islands, where they had previously been abundant.
About the same time, residents of the Orkney Islands off the north coast of Scotland were several times startled by the improbable appearance on their shores of Inuit people in kayaks, presumably forced south and east by enlarging ice packs to the north.
Poor harvests and harsh weather, together with the promise of better life elsewhere, initiated emigration from Scotland that would continue for centuries.
Perhaps one of the greatest difficulties faced by people of the time was unpredictability.
While it might be possible to adapt agriculture and housing to consistently lower temperatures, it was very difficult to cope with wild swings between very cold and very warm.
And weather records, which are quite complete for much of Europe and parts of North America from the early 1600s on, show that climate extremes were often juxtaposed.
The coldest winter in central England between 1659 and 1979 was the winter of 1683–84; one of the warmest was just two years later in 1685–86.

Not all of the news from the Little Ice Age was bad.
Countries such as Holland benefited from the shift of fish stocks southward into the North Sea.
In response to coastal flooding, exacerbated by the violent storms of the sixteenth and seventeenth centuries, the Dutch also became experts in the technology of reclaiming lowlying land from the sea.
Subsistence farming, always risky at the best of times, declined during the Little Ice Age, and more specialized agriculture sprang up, especially in Britain.
Growing cash crops for the city was usually a better way to survive than trying to be self-sufficient.
Even glass windows are believed by some to be a response to the cold temperatures of the
Little Ice Age—they helped keep the cold out but still provided a view of the outside world.
And while no one has yet suggested any connection between climate and the American Revolution, it is quite likely that the chronic shortages of bread and grain in France in the late 1700s, which were due at least partly to the bitter winters, unpredictable climate shifts, and generally bad weather of the time, fed the underlying discontent that led to the French Revolution.

The Little Ice Age even influenced art.
Snowy winter scenes suddenly appear abundantly in sixteenth-and seventeenth-century European paintings.
Skaters glide on canals and lakes that have not been frozen in living memory (figure 26).
In 1970, Hans Neuberger, a meteorologist at Pennsylvania State University, analyzed more than twelve thousand paintings from American and European museums, all dating between 1400 and 1967.
He classified them by region and date, and looked at them with a meteorologist’s eye.
Neuberger was particularly interested in depictions of the sky, and while not every painting was amenable to this kind of examination, many were—even if they only showed a glimpse of the sky from a window.
While artists surely take some license with their subjects, Neuberger’s analysis uncovered some clearly defined trends—for example, none of the British paintings he studied showed a completely clear sky, while some 12 percent of those from Mediterranean countries did.
Half of the British paintings showed the sky completely overcast, a higher fraction than any of the other regions he studied.
His data show an increase in cloudiness between 1400 and 1550, and then an abrupt further increase—more than 50 percent—especially in the abundance of low, scudding clouds.
Cloudiness peaks during the seventeenth century but remains high throughout the Little Ice Age.
Neuberger also pointed out that most paintings from the last few hundred years of the Little Ice Age—on average its coldest period—are very dark compared to both earlier and later art.
This could just be a popular stylistic device, but Neuberger suggests that it might also be a reflection of the generally cloudy, low-illumination conditions that prevailed.

Figure 26.
Painting by Sir Henry Raeburn of the Reverend Robert Walker skating on Duddingston Loch, near Edinburgh, Scotland, toward the end of the Little Ice Age.
Duddingston Loch rarely freezes in winter now.
Reproduced with permission of the National Gallery of Scotland.

And in 2003, Henri Grissino-Mayer, a tree-ring expert at the University of Tennessee, and Lloyd Burckle, at Columbia University, suggested yet another possible connection between the arts and the Little Ice Age: they proposed that climate may be partly responsible for the exquisite sound of Stradivarius violins.
By examining tree rings,
Grissino-Mayer found that growth in European high-altitude forests slowed because of the cold of the Little Ice Age.
He also discovered that between 1625 and 1720, the trees showed exceptionally narrow growth rings, producing dense and strong wood—properties that may have enhanced the quality of the instruments made by the renowned Italian craftsman.
Stradivarius produced his most famous violins between 1700 and 1720.