The Little Ice Age: How Climate Made History, 1300 to 1850 (2000) by Brian Fagan

There is no bigger topic on the global stage today than climate change. The primary culprit causing today’s climate crisis is hydrocarbon emissions, a process that kicked off a century and a half ago with the Second Industrial Revolution. But there was something about this widely accepted narrative that has always troubled me and it had to do with Boston Harbor. In 1775, General Thomas Gage, governor and commander in chief of British forces in Massachusetts, was surrounded by hostile colonial insurgents. Gage felt compelled to remove his fleet of Royal Navy warships from Boston before the harbor froze over, which it did every year. Yet, a short seventy five years later when Boston was in an uproar over southern slave hunters coming to Boston to hunt down escaped slaves under the new Fugitive Slave Act there is no mention of worries about Boston Harbor freezing over. How could this be? Whatever the cause of the remarkable warming of Boston in the nineteenth century, hydrocarbon emissions certainly wasn’t it.

One plausible explanation is that the frigid Boston weather of the late eighteenth century was the tail end of a half millennium mini ice age that gripped the entire world. “The Little Ice Age: How Climate Made History, 1300 to 1850” (2000) by Brian Fagan tells the story of how shifts in high and low pressure zones in the northern hemisphere dramatically altered ocean currents, which in turn dramatically altered weather patterns across western Europe and beyond. Unlike today’s climate change, which has resulted in monotonic increases in global temperatures for one decade and the next, the Little Ice Age “was an endless zigzag of climatic shifts,” Fagan says, “few lasting more than a quarter century.” These climatic changes have been accurately recorded over centuries in tree rings and ice core samples.

This was a significant and unwelcome change from the warm and stable weather pattern known as the Medieval Warm Period experienced from 900 to 1200, which were four of the warmest and most climatically stable centuries of the past 8,000 years. Fagan says that these centuries were a “climatic golden age,” which is interesting considering that it was even warmer than it is today. Average summer temperatures were two degrees fahrenheit warmer than they are today even after decades of global warming. In fact, the period of time known as the Holocene, the last 12,000 years since the last glacial Ice Age, has been “an endless seesaw of short-term climate change caused by little understood interactions between the atmosphere and the oceans,” Fagan says, a perspective that hardly fills one with confidence in the accuracy of modern climate models.

No natural phenomenon is more important to Fagan’s climate research than the North Atlantic Oscillation (NAO), a seesaw of atmospheric pressure between a persistent high over the Azores and an equally prevalent low over Iceland. The NAO Index is considered “high” when it follows this pattern of low pressure over Iceland and high pressure over Portugal. This high NAO Index condition creates persistent westerly winds blowing in from the Atlantic, which tends to keep winters mild and the agricultural growing season long. When the NAO Index flips to low, with high atmospheric pressure over Iceland and low pressure over Portugal, westerly Atlantic winds weaken, allowing much colder air from the arctic to push down into western and central Europe. Fagan says that these swings from high and low NAO Index are sudden and unpredictable, but most likely are related to sea surface temperatures in the North Atlantic. “We do not know what causes high and low indices,” Fagan writes, “nor can we yet predict the sudden reversals that trigger traumatic extremes.”

The Little Ice Age kicked off around 1315 with an extended period of cold and wet that decimated European agriculture. Harvests of cereal crops and other critical foodstuffs dropped by almost half. The suffering lasted seven years. The cycle ended with the reversal of the NAO in 1322, which traded flooding for bone chilling cold. Western Europe was devastated by bubonic plague in the late 1430s, a disaster that was compounded by exceptionally harsh winters and extended frosts that led to crop failures and food crises.

As bad as all of that was, the coldest and most difficult years of the Little Ice Age occurred in the late sixteenth century, Fagan says. Famine followed famine as severe storm activity increased by almost 400 percent. More than a thousand people in the Bern, Switzerland region alone were accused of conjuring up bad weather and were burned at the stake for witchcraft. In the small German town of Wisenstieg, 63 women were burned in 1563 alone. Meanwhile, in 1588, the infamous Spanish Armada was smashed more by the treacherous weather than any sea battle with the Royal Navy. Extreme weather also likely destroyed the early New World Spanish colony of Santa Elena in present day South Carolina in 1565 and the British colonies at Roanoke in 1587 and Jamestown in 1607.

So what caused the Little Ice Age? Fagan again says “there are no easy answers,” but some obvious explanations, such as anthropogenic causes, can safely be eliminated. More likely, he says, it was slow, natural, and cyclical changes in the eccentricity of the earth’s orbit and in the tilt and orientation of its spin that have changed ocean circulation so profoundly, which in turn dramatically affects the earth’s climate patterns. This change in the “Great Ocean Conveyor Belt,” as it is sometimes called, affects more than just weather. It also affects ocean temperature, which in turn affects global fisheries. For instance, cod fish thrive in a narrow band of ocean temperatures between 39F to 44F. During the Little Ice Age, ocean temperatures shifted dramatically enough to push the great schools of cod fish from the waters of continental Europe all the way to the Great Banks of North America, a shift that Fagan says played an important role in pushing European powers to innovate open ocean ship designs, such as the three mast English “dogger” capable of catching 30 tons of fish with a crew of ten. The Europeans could now sail anywhere around the world confidently, but nothing trumped the value of the cod fish, which Fagan says “endured far longer than the gold of the Indies.”

Meanwhile, agricultural practices improved dramatically across Europe. The Dutch reclaimed a third of their total farmland between 1600 and 1650 using new techniques for drainage, which Fagan says helped create the first modern economy in Europe. New high calorie crops, such as turnips and potatoes, were introduced that broke many countries free from “the tyranny of cereals,” according to Fagan. The potato was first brought back from South America to Europe in 1570. Fagan says that “the wealth generated by the potato would exceed all the gold and silver exported from the Americas.” Today, a single year’s global potato harvest is worth $100 billion. The potato is not only nutritionally rich, it’s also incredibly easy to grow. Ten men can turnover and sow 0.5 hectares with potatoes in a day. A cereal crop of the same area in the same amount of time would take over forty men. That little half hectare can produce over 8 tons of potatoes. Despite its many nutritional advantages, the potato was adopted quite late and reluctantly across several European societies, such as the French, which still resisted the potato as late as 1750 (the backwardness and subsistence cereal-based nature of French agriculture that was highly vulnerable to climatic shocks is a theme of this book). But in Ireland the potato was widely adopted; so much so, Fagan says, that the economy was dangerously reduced to a monoculture, which had devastating effects when the potato blight hit in 1845 and killed up to half the crop. Fagan says that total human losses in the Irish potato famine from 1845 to 1848 (also known as the “An Ghora Mor” or “The Great Hunger”) may never be known, but it’s likely well over one million people died out of a population of 8 million, while another million plus people emigrated. Incredibly, the Irish population didn’t fully recover from the famine until the 1960s.

In addition, new farming techniques, enclosed fields, more extensive manuring, and improved drainage systems all bolstered yields per hectare. These innovations insulated Western Europeans from the worst effects of sudden climate changes associated with the Little Ice Age and flip-flopping NAO. The early eighteenth century was so cold that Iceland was largely icebound and some years it was possible to walk from Denmark to Sweden to Finland on the frozen Baltic Sea. Fagan writes that “Apocalyptic famines” in 1693 (which killed 10 percent of the entire French population) and 1740 were as bad as that of 1315. The author says the compounding implications of poor agricultural practices combined with severe weather was a triggering event of the French Revolution. “The Great Fear was, in the final analysis,” Fagan writes, “the culmination of a subsistence crisis that had brewed for generations, of a chronic food dearth triggered by draconian land policies and sudden climatic shifts that pushed millions of French peasants across the fine line separating survival from deprivation.” The last “truly extensive food dearth in the Western world” came in 1816 with the eruption of Mount Tambora in modern day Indonesia. The intense volcanic eruption blanketed the earth in ash and shortened the growing season from 155 to 100 days in many parts of the northern hemisphere. The effects were so extreme that it generated new policies by governments to provide basic security and social welfare, an outcome which Fagan calls “the greatest legacy of the Tambora eruption.”

The first man-made activity that significantly impacted the climate was not the burning of coal during the Industrial Revolution, but rather the widespread pioneer agriculture and land modification that took place with Manifest Destiny in the United States during the first half of the nineteenth century and similar European colonial exploitations around the world. Fagan says that a standing forest contains as much as 30,000 metric tons of carbon per square kilometer in its trees, while virgin grassland soils contain up to 5,000 metric tons in the same space. When the trees are cut down or the soil is cultivated, much of this carbon enters the atmosphere. Fagan says that the heavy deforestation and farmland reclamation between 1850 to 1870 may have raised the carbon dioxide level in the atmosphere by ten percent. Since then, atmospheric concentrations of carbon dioxide have increased by 30 percent. Other greenhouse gas emissions, such as methane from cattle herding and rice paddy production, have contributed to the problem as well. Methane levels in the atmosphere have roughly doubled since the Industrial Revolution. The upshot has been that global mean surface temperatures have risen between 0.4 to 0.8 degrees celsius since 1860. “It is surely no coincidence that global temperatures have gradually and inexorably risen over the past 150 years,” Fagan says.

Scientists were aware of this unusual persistent warming trend as early as the 1940s, although cold snaps in the 1970s had some folks talking about another impending ice age. In 1988, in what Fagan says was a seminal event, climatologist James Hansen testified before a hearing of the Senate Energy and Natural Resources Committee arguing that promiscuous use of fossil fuels had put the global climate systems on a sustainable trajectory of higher temperatures. The resulting 150-year sustained warming trend is now the longest in over a millennium. Summer temperatures are now equal to the means of the Medieval Warming Period. Meanwhile, the NAO has remained in high mode for decades longer than normal.

In closing, Fagan offers up two simple takeaways from the Little Ice Age. First, climate change often comes in sudden shifts, not gentle, easy stages. Second, climate change has a profound and possibly even decisive influence on human events. Personally, my main takeaways were that ocean currents and atmospheric high pressure systems dominate climatic cycles and that we have very little understanding how it all works.