Climate change deniers often say the climate is always changing and there’s nothing we can do about it. To support their view, they point to the so-called Little Ice Age, a generally cooler period from approximately 1350-1850 AD. The deniers also suggest that a similar decline in temperature will happen sooner or later no matter what humans do. A typical article begins: “Contrary to the conventional wisdom of the day, the real danger facing humanity is not global warming, but more likely the coming of a new Ice Age.” In July 2015 a headline in London’s Daily Mail asked: “Is a mini ICE AGE on the way? Scientists warn the sun will 'go to sleep' in 2030 and could cause temperatures to plummet.”
Such articles are full of errors, according to new research reviewed by Tim Radford of the Climate News Network. Radford says that compared to what is happening now, the new research shows that climate change in the Little Ice Age seems to have been “small-scale, seasonal and insignificant.” In his review dated April 18 and titled Current climate makes Little Ice Age look puny, Radford writes:
The famous Little Ice Age, when Londoners could roast oxen on the frozen River Thames, may not have been so icy after all – and “little” might indeed have been the appropriate description.
The new research reviewed by Radford was published on April 1 in the Astronomy & Geophysics Journal of the Royal Astronomical Society. Frost fairs, sunspots and the Little Ice Age, by Lockwood et al., examines the solar Maunder minimum, the Little Ice Age and the freezing of the Thames River to ascertain the links between these events, if any. Lockwood says the British team of five researchers wanted
to carry out a comprehensive study to see just how reliable the evidence is for a cooler climate, how big an impact it really had, and how strong the evidence for a solar cause really was. climatenewsnetwork.net/...
According to the new research, average temperatures may have fallen by 0.5°C (0.9°F) during the Little Ice Age, but occasionally there were very warm spring and summer months even after a fiercely cold winter. In contrast, during the most recent ice age that ended about 12,000 years ago, average temperatures fell about 8°C (14.4°F) and thick ice sheets covered Scotland. These findings were based on evidence compiled over the years by many scientists using a variety of paleoclimate techniques and a vast number of measurements from ice cores, tree rings, coral growths, and counts of fossil shellfish and insects. In addition, the research team consulted the Central England Temperature records which began in 1659.
To show how cold the Little Ice Age might have been, climate change deniers often describe the frost fairs that were sometimes held when the Thames River froze solid. However, there are records of much earlier events on the frozen river, including two that occurred in 250 AD and 695 AD, and there is a record of fires and sports on the Thames in 1309. Records also show that frost fairs were not always held when the river froze:
In the winter of 923, the river carried loaded horse carts for 13 weeks and in both 1150 and 1410 the same was true for 14 weeks, but no frost fair is mentioned in the records….
between the frost fairs of 1763 and 1789 there were five winters in which the Thames was reported as freezing, yet there is no record of a frost fair being held. academic.oup.com/...
Frost fairs on the Thames were often “bawdy and unruly” events which authorities may have wanted to prevent. This may explain why there are no reports of them in some extremely cold winters. Health may have been another reason. During the very cold winter of 1776, an influenza epidemic killed an estimated 40,000 people in England and was probably the reason for no frost fair when the river froze that year.
The authors of the paper object to the term LIttle Ice Age for two reasons. First, many people mistakenly think the period was similar to a “full” or “proper” ice age, which lasts thousands of years and which Radford says “can be linked to slow changes in the planet’s orbit around the sun.” Second, many people also mistakenly think the Little Ice Age was caused only by lower solar activity such as occurred between 1645 and 1715, a period called the Maunder minimum. The Daily Mail article with its alarming headline about the sun going to sleep refers to the Maunder minimum as “a mini ice age when it hit between 1646 and 1715, even causing London's River Thames to freeze over.“
Two possible causes of the Little Ice Age are discussed in detail in the study: volcanic activity and lower solar activity. Volcanic eruptions sometimes result in lower global temperatures because they inject huge quantities of dust into the atmosphere. The researchers found there was “almost continuous” volcanic activity between 1570 and 1730, when the lowest temperatures were recorded in the Little Ice Age. “The year without summer” (1816) occurred after the huge Tambora eruption in Indonesia in 1815.
Studying the records of solar activity, the researchers found there was no “straightforward connection” between sunspot variations and variations in temperatures. At times, lower temperatures followed some periods of low solar activity, but not at other times. However, the lowest temperatures of the Little Ice Age did occur during the Maunder minimum (1645-1715) when the sun had almost no sunspots. For this reason, many people associate the Little Ice Age with the Maunder minimum.
The new research shows that the Little Ice Age may not have been as cold as some believe, and sunspot activity was not the only factor at work. In addition to volcanic and solar activity, other factors mentioned in the paper include changes in ocean currents and normal climate variability.
Frost fairs, sunspots and the Little Ice Age covers many subjects of interest. For example, it explains how temperatures 420,000 years ago can be deduced from ice cores taken in the Antarctic. Briefly, more deuterium and an isotope of oxygen will be found in polar ice cores if global temperatures were higher when they were deposited, and less if temperatures were lower.
Global temperatures can be inferred from polar ice cores, using the isotopic composition of the water molecules. In particular, the amounts of deuterium (2H) and of the 18O isotope present in the ice are lower if temperatures at lower latitudes at the time of their deposition were depressed. This is because it takes more energy to evaporate the water molecules containing these heavier isotopes from the surface of the ocean.
In addition, when the warm air containing the evaporated water cools as it moves toward the poles, the water molecules containing the heavier isotopes are “more easily lost by precipitation.” As a result, if global temperatures are lower, less deuterium and the oxygen isotope reach the polar regions.
The paper has several charts and graphs. This one published in 1999 shows the variation in global temperatures over 420,000 years.
The paper also makes use of paintings to reveal conditions during the Little Ice Age. One shows the frost fair of 1684 with the Old London Bridge in the distance. It is significant because the bridge slowed the river and thus allowed the ice in very cold winters to thicken enough for a fair. After the bridge was removed in 1825 and more embankments were built, the increased speed prevented much more freezing. As Radford says, during the time of the great frost fairs, the freezing of the river was more probably linked to the Old London Bridge than to solar activity.
In his review Radford quotes the leader of the study, Mike Lockwood, a professor of space environment physics, about the implications of the study for the future. Lockwood says that as we confront current global warming, the Little Ice Age described by the new research cannot be an “excuse for inaction.” Any cooling that results from a decline in solar activity, the professor warns, will be “more than offset” by rising emissions of carbon dioxide.
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UPDATE: Some comments on the diary discuss the causes and effects of the Little Ice Age. Many thanks to all the commenters:
Yamaneko2: “Another possible culprit for the mid-millennium minimum could be afforestation pulling CO2 out of the atmosphere as human populations in certain localities fell. The first demographic disaster would be the Black Death, starting in 1334 in China then proceeding westward until landing in Crimea and Constantinople (and our history books) in the mid-1340s. Over the next decade most of Europe got hit. One result of this would be significant afforestation in Europe as lands recently cleared reverted to forest. Afforestation takes about 50 years, if the experience of forest regrowth in New England is instructive. The next disaster would be the first wave of disease in Mesoamerica during the Spanish conquest. This would be followed by the disastrous decline in Native American populations during the early 1600s as Native-maintained parklands reverted to wild forests.” www.dailykos.com/… However, Keith Pickering replies: “Ice core records show pretty clearly that CO2 levels were quite stable for thousands of years before the industrial revolution.” www.dailykos.com/...
wu ming: “the little ice age was serious business, and killed off a whole lot of people through its after-effects. that we’re in the process of messing up global temps by an even larger margin through carbon emissions is rather terrifying….in particular, temperature and climate change wreak havoc on complex societies based upon the presumption of a stable and predictable climate, both temps and precip. we like to think of ourselves as totally beyond agriculture these days, calling ourselves an industrial economy, or an information economy, but as we saw in the syrian civil war and the arab spring just a few years ago, it doesn’t take much in the way of crop failures to undermine the very foundation of a society.” www.dailykos.com/…
RocketRaccoon: “There were a number of Icelandic volcanoes erupting in the late 15th and early 16th centuries; most of the eruptions were followed in the next year by crop failures in northern Europe and the British Isles.” www.dailykos.com/…
leftlalngler: “And yet that small change in climate had profound impacts on history, see Brian Fagan’s The Little Ice Age ( and also The Long Summer , and Fish on Fridays, and anything else he’s written….)” www.dailykos.com/…
askyron: “my wife did research on the little ice age for a fiction book she wrote. A few of the accounts included birds dying out of the air, and the ocean around the area freezing out a couple of miles. That is much more impressive a freeze than the river freezing.” www.dailykos.com/...
Bobs Telecaster: [global temperatures deduced from ice cores are not] “terribly useful locally, which is the only data geologists can work with. We have two large still-frozen bodies where we can get ice core samples, which is where you get precise data….. The rest we can only infer from in situ fossil pollens or foraminifera, glacial striations, deep sea sedimentary core samples, and other paleoclimatic indicators tied to the place you’re examining. These can’t usually yield that kind of precision, but can tell you enough….” www.dailykos.com/…
environmentalist: “
It has also been my understanding that the Little Ice Age was, for the most part, a regional event. It was limited to the northern hemisphere and in particular to Europe. It was not a world-wide event.” www.dailykos.com/…
PrufPupDog: “The last paragraph is key. Under natural conditions, orbital variations could be driving the earth into a cooler climate; however, human activities (carbon dioxide emissions) more than offset the natural change and drive climate in the opposite direction. That was concluded by Hays, Imbrie and Shackleton in Science way back in 1976.” www.dailykos.com/…