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IAn elephant walked across London’s Thames surface near Blackfriars Bridge on February 1, 1814. The stuntDuring the Frost fairWhen temperatures plunged to -0 degrees Celsius for four days. Londoners held a festival immediately, complete with pop-up stores and a lot more unlicensed alcohol.
It was the last Thames frost fair. They had been taking place at irregular intervals for several centuries, and they were occurring every few decades. One of the most renowned fairs took place during 1683-84’s Great Frost. It saw the birthof Chipperfield’s Circus. However, the river in central London is not frozen since 1814.
The frost fairs are perhaps the most emblematic consequences of the “little ice age”, a period of chilly weather that lasted for several centuries. While Londoners enjoyed the ice, other communities were faced with crop failures and other threats. The story of the little Ice Age is one of societies that had to adapt to changing circumstances or perish.
It’s also a long-standing mystery. Why did the climate change and why did it remain that way for so many centuries? The result of decades of research is finally coming to an end. The emerging story involves volcanoes as well as the oceans, possibly also the sun and possibly genocide.
A question of degree
Like many things in science, the little Ice Age was discovered slowly and incrementally. “This all came about because there were lots of documentary records from around Europe, stating that there were some really cold winters,” says climatologist Paola Moffa-SánchezDurham University. These were reflected in records of grain prices, which rose because of crop failures and ships’ logs saying Greenland was surrounded by sea ice and unreachable.
The term “little ice age” was coined by a Dutch-born geologist named François MatthesWho is the in? A 1939 reportIt was noted that the Sierra Nevada glaciers, California, had regrown at one point in the past few millennia. The term StuckHowever, it took decades for the timeframe to be narrowed.
This was done by British climateologists Hubert LambHe later founded the University of East Anglia’s Climatic Research Unit. In A study published in 1965, Lamb used European temperature records going back mAny centuries to identify a “notably warm climate… around AD1000–1200” that was “followed by a decline of temperature levels till between 1500 and 1700 the coldest phase since the last ice age occurred”. This chilly period was “undoubtedly upsetting for the human economies of those times (and perhaps of any time)” [his italics].
The little ice age has been difficult to quantify for climatologists since then. Most of the records proving the cooling come from Europe. RecordingsIt is not always obvious when it comes from another source.
“It’s not a global phenomenon, in that it wasn’t cool everywhere,” says Alexander Koch at Simon Fraser University in Burnaby, British Columbia, Canada. The period was warmer than normal in some places, such China.
What’s more, “the cooling was not continuous”, says Dagomar Degroot of Georgetown University in Washington DC. “It came in waves… that reached different places at different times at different magnitudes.”
It is difficult to determine the exact date of the little-ice age’s beginning and ending. “The classical definition is between 1400 and 1850,” says Moffa-Sánchez. However, “some people say 1300 to 1850”, pushing the start date back significantly. There is broad agreement that the period 1400-1800 is within the little ice age, she says, but outside that it’s fuzzy. Either way, the 1814 frostfair was close to the end.
The little ice age wasn’t technically an ice era. These are periods during which Earth has permanent Ice at both Poles. We have been living in one for more 2.5m years. The ice sheets have been changing and shrinking over that time. The most recent ice advance, which we colloquially call the ice age but is really a glacial period, occurred from about 115,000 to 11,700 years ago. We have been living in the Holocene, a relatively warm period.
In this context, the little Ice Age is minor. “We’re talking about several 10ths of a degree C,” says Degroot. Degroot says that the coldest part of the last glacial period was, however, About 6C coolerMore than the past 4,000 year. Degroot says that even this minor change made a difference. “On a regional or local scale, the anomalies could be really quite extreme,” he says, and documentary evidence shows that “at least some people were aware that they were living in an anomalous kind of climate”.
Mystery cooling
What was the secret? The story isn’t entirely settled, but researchers are increasingly confident about the initial trigger: volcanoes.
“You have these eruptions that are happening in clusters,” says Degroot. A 2015 studyData from ice cores was used to identify 25 major eruptions over the past 2,500 year. There were between 1200 and 1400 eruptions. huge eruptions of the Samalas volcano in Indonesia, Quilotoa in Ecuador and El Chichón in Mexico.
The stratosphere, the layer above the weather, is where large eruptions can blast sulphate sulfate aerosols. These aerosols reflect some of the sun’s rays back into space, cooling the Earth. Recent events include the 1991 eruption of Mount PinatuboIn the Phillipines, triggered Up to 0.5C of surface cool.
A volcanic eruption typically cools the climate for a few decades. “But if you have big eruptions in clusters, that can set off positive feedbacks in the climate system,” says Degroot. For example, years of lower temperatures can cause Sea ice to expand. Sea ice, which is white, reflects more radiation back into the universe than dark blue water. “That can prolong and exacerbate the cooling,” he adds.
There can also be knock-on effects in the ocean, says Moffa-Sánchez. If the winds change, large rafts can be carried southward from Greenland to the Atlantic by sea ice. Labrador Sea. They interfere with the enormous Atlantic currents that transport warm water from the Tropics to Europe.
This is a complicated story. The initial cooling caused by volcanoes can trigger changes in the Earth’s system that result in more and longer cooling. But it seems to be true. A 2018 modelling studyAlthough it was impossible to explain the little-known ice age without citing volcanic eruptions, that does not mean that other factors are not at work.
A star that is slowly fading
The sun is another possible factor. The amount of energy it produces varies wildly, most notably over the 11-year solar cycles, during which activity changes from a maximum level to a minimum. The effects on Earth are so small they’re hard to detect, but the sun sometimes has more of an impact.
Several times in the past 1,000 years, our star has entered a “Grand minimum”, in which it spends several decades being less active. The Dalton Minimum was the most recent, between 1790-1820. This was preceded the Maunder Minimum between 1645-1715. Before that, there is thought to have been the Spörer Minimum between about 1460 and 1550 and the Wolf Minimum around 1280-1350. Even though such grand minima can cool down the planet, Not more than 0.3CAnd probably even less.
Grand minima probably played a role in some of the chilliest episodes, says Moffa-Sánchez. In her studies of the period, “cold centuries coincided with these really famous solar minima.” She has found evidence that grand minima affect wind patterns, with knock-on effects for ocean currents and heat distribution.
However, it seems unlikelyThe little ice age was caused by grand minima. The timings don’t fit and, in any case, the climate impacts of grand minima are much smaller than those of massive eruptions.
It could be that a solar maximum in late 1300s also played an important role. A studyPublished in December 2021, this study found that this altered wind patterns, interfering the crucial Atlantic warm water current.
The key point is – this isn’t an either-or debate, says Moffa-Sánchez. “It’s a likely combination of all of them.”
There are many reasons why the climate shifts occurred in waves. “It was not that you had this little ice age period where it was always cold,” says Moffa-Sánchez. “You just had several cold centuries throughout this four-century-long period.”
One problem remains. The coldest period of the little ice age was around 1610 and it doesn’t coincide with a grand minimum. Nor was there a particularly big eruption: Peru’s HuaynaputinaIt was taken off 1600, but while the blast was large it wasn’t exceptional.
Instead, the suggestion is that this cold spell was caused by humanity – in a truly horrible way.
The great dying
Christopher Columbus reached Americas in 1492. Over the next decades, Europeans began colonizing them. They fought with Native Americans, often resulting in their deaths. Even more dangerously, they brought diseases. One of the most deadly was smallpox that claimed millions of lives.
This may have had an impact not only on the climate but also as a genocide. Many Indigenous Americans were farmers, who had cleared forests for crops. After they died, the trees grew again, drawing carbon dioxide out the air and cooling down the planet. This is the scenariowas first described by climatologist William RuddimanIn 2003, as part of his “Anthropocene early” hypothesis that humans have been affecting Earth’s climate for millennia, albeit less than we are today.
The idea that climate cooling is caused by mass deaths in Indigenous Americans has received a lot of attention. Support tentativeFrom modelling studies. It has been. controversialBecause of the uncertainty surrounding key numbers.
Koch and his coworkers published an article in 2019. Updated analysis. They went through the argument one by one and attempted to quantify everything, including the number of people who died and the extent to which reforestation occurred. They concluded that the European arrival had caused 56m deaths by 1600. This horrendous toll led to trees growing again on 56m ha of land, removing 27.4bn tonnes of carbon dioxide.
“It’s a really interesting theory,” says Degroot. However, he remains sceptical because we don’t know how land use was changing in other parts of the world, especially Africa.
Resilience
While the question of whether human society contributed to the little ice agee remains up for discussion, what’s clear is that the little ice age affected human society.
Norse settlers, for example, made Greenland their home in 985. They stayed there until the early 1400s, when they left. It has been suggested that the little-known ice age played a significant role in this. However, A March studyThe sediments in the region were examined and showed no evidence of cooling. However, it did show signs of cooling. A drying trendThis would have meant that there was less grass for livestock to graze.
Such stories may be true, but it’s crucial to remember that people were not passive victims, says Degroot. “You don’t just see people who are completely at the whim of changing climatic conditions, you see people changing adaptively.”
Degroot points out the Arctic, which saw remarkable activity despite an increase in sea-ice. Between 1611-1619, European Whalers Operated off the coast of SvalbardBecause of a shortage, vegetable oil and whale oils were used as a substitute.
The Dutch Republic considered the period between 1560-1620 to be part of the “period” a golden ageDespite or because of the cold winters. Degroot says that the republic did not rely on local agriculture so crop failures were less of an issue. Instead, the republic’s economy was driven by merchant ships, whose operators devised ingenious ways to cope with the cold – and the Dutch thrived while their neighbours struggled.
“It so rarely is what you’d expect,” says Degroot. Understanding how past societies dealt with climate shifts such the little Ice Age will help us all as the climate crisis gets more severe. “Hopefully, we can learn from them, figure out what they did right, what they did wrong.”
We need to learn quickly, as the little ice age was only a taster. Back then, the average global temperature cooled by a fraction of a degree, but we’ve already Warm it up to 1.1CThese are the set to Keep your temperature above 1.5CIn the coming decades.
