The Little Ice Age; was it big enough to be global?

This Weather topic submitted by Andrew Daley ( on 5/8/98.

"Our years are turned upside down; our summers are no summers; our harvests are no harvests"
-John King, 1595

Though it may appear to be, the earth and its surroundings are far from perfectly stable and constant. We humans find it quite easy to understand daily and seasonal Weather fluctuations as being perfectly normal. But when longer-term fluctuations, cycles, and changes in our Climate are considered, it becomes harder and harder for us to imagine these things about the earth that seem so infinitely static to us as, in truth, dynamically inconstant and defined by change. The planet's crust is steadily being stretched and bunched up like a baggy sweater; our Earth wobbles on its axis like a top and deviates on its course around an inconsistent sun. These are hard things for us to imagine considering that we view these changes is such a minutely small increment; that is to say, merely a lifetime.
Nevertheless, small blips in the Progression of the Climate can appear to (as an the Elizabethan preacher quoted above believed in 1595) make everything 'turn upside down'. This is certainly the case to a number of people who lived through what has been called by some the most recent "dramatic shift in Climate", The Little Ice Age of 1550-1700. During this 'reign of cold', the global average temperature dropped between 1 and 2 degrees Celsius for a span of several hundred years. Ice sheets advanced over farms, villages, valleys...Greenland (Seabrook A1). The Baltic Sea and the Thames River froze regularly. Crops failed; famine and disease defined Europe (Schaefer 35). Sea Ice surrounded Iceland occasionally during this time to the extent that, from the highest point of the island, one could not see the ocean (Lamb 15). Glaciers around the globe advanced during this time, and have only beginning to recede in the 20th century. According to some "the rates of famine and mortality increased all over the world" as a result of the Little Ice Age (Schaefer 35).
Centuries of personal accounts, harvest records, and scientific data exist that tell of the effects of this period of cold (Appleby, Pfister, Vries). But, almost all of this information is European in origin. Whether or not the better-termed European Little Ice Age was in fact a global phenomenon is an important question. Beyond any doubt, the period of cold in the 16th, 17th and 18th centuries had drastic affects on many Europeans, but the question remains to whether the rest of the world's population (which is by far the majority of the people) experienced similar disruptions. In this paper, I seek to explain the physical and human consequences of this climatic event (spanning regions and continents) in order to determine if it was a global phenomenon, and discuss the possible causes of the Little Ice Age.

Ice Ages and Glaciers
What is an 'ice age' necessarily? And what is a 'little' one for that matter? The defining characteristic of an 'ice age' is the uniform, global advance of glaciers and sea ice. How is this so? The advance of glaciers and sea ice are primarily the result of a decrease in climatic temperature. This is true because of the very nature of what makes a glacier form. Glaciers are the accumulation of years of snow that had fallen in winter months, yet did not melt in the summer. As more and more layers are deposited, the snow is compressed, changes into ice, and is compacted more and more densely with each succeeding year. At a critical depth, approximately 18 meters, the ice sheet begins to move as a result of its own weight and gravity. Although ice within a glacier is always moving (like a conveyor belt), if the amount of annual accumulating snowfall which feeds the glacier equals the amount of ice that melts, then the glacier will sustain its present frontal 'terminus' position. But, "glaciers periodically retreat or advance, depending on the amount of snow accumulation or ice melting they experience" (Cheshire 3). The extent of these retreats and advances depends on (1) the type of glacier (expansive ice sheet glacier, mountain glacier, valley glacier, tidewater glacier, etc.), (2) precipitation, and/or (3) temperature. The question is, then, is there a general advance of glaciers around the world during the time of the Little Ice Age?

Glaciers and Greenland
The period before the Little Ice Age was in fact preceded by a several hundred-year period with generally warmer-than-average temperature conditions. During this time, Greenland (which was actually green during this warm period) was settled near the end of the 10th century. From 1000-3000 CE, the colony flourished: a cathedral was built, a monastery and a nunnery existed, and more than 3,000 colonist lived on 300 farms. But as the Little Ice Age approached, Weather continually degenerated for the colonists. Harvests failed, settlements to the north were abandoned as the permafrost level rose and glaciers spread south. In fact, today archeological studies of the Greenland colony date graves based on how shallow the coffin was buried because of the increased permafrost level over time.
Personal accounts, like those of a trader in 1751, tell the story of glacial advance: "The ice increases every year, which is mostly recognizable from the fact that tracks where the Greenlanders used to go hunting are now quite overridden and covered by ice, and, as far as may be concluded from their simple chronometry, the change that has taken place in a score of years is very considerable" (Grove 266). Due to the high latitude of their settlements, the people of Greenland were hard hit by glacial advance of "ice which has laid itself over the entire hinterland" that buried many northern settlements (ibid).
Of the Research done after the 19th century in Greenland glacial sheets (203 in all) the Study of their movement 'strongly suggests' that the dominant determinant of their movement is temperature. That is to say, glacial advances and retreats in Greenland over the past hundred years reflect shifts in lower and higher than average temperatures during this time. It is possible to assume, therefore, that this is also the case with the major glacial advance during the Little Ice Age. The next question, then, is what about the other regions of the world? Were there coinciding advances? And if there were, are they the result of temperature or some other factor?

Glaciers in the Southern Hemisphere during the Little Ice Age
In actuality, very little is known about many of the glaciers in Africa and South America, presently and historically. "These are amongst the least known of the world's glaciers. All -or nearly all- of them have retreated in the course of this century, but information about the timing of their fluctuations in earlier centuries is sparse" (Grove 264). With lack of information on glaciers during the 16th, 17th and 18th centuries even a problem in Europe, it is even more difficult in the Southern Hemisphere (or anywhere else other than Europe, for that matter) to be precise about the fluctuations in glacial frontiers over the past four to five hundred years. As can be seen in the following graph of Switzerland glacier, very few Sources (individually represented as hash marks) show up until the 1800's. Frontal positions can only be determined on broad, possible imprecise terms for the majority of glaciers of the world.
In spite of this, moraines (elliptical shaped debris deposits left during a glacial recession) of a significant number of glaciers in southern Patagonia, South America, point to a general advance culminating in the 17th, 18th, and 19th centuries, and then followed by a 20th century recession. As early as 1895, in fact, it was observed that "the present glaciers (of South America) clearly indicate not only that until a short time ago they were of much greater extent but also that they are now losing volume and receding at a great rate" (Hauthol, 1895 in Grove 273). For example, on the western edge of the Cordon Limite in southern Patagonia, the Ada glacier was observed in 1858 to reach down to 1,797 meters; by 1882 the front had risen to 1,929 meters and in 1980, it had risen further to 2,500 meters above sea-level (Groeber 168).
As well, observations of the snow-line in the Andes since European arrival show an overall retreating tendency in the snowline (See diagram).xxxx
In New Zealand, where much more Research of the glaciers on its two islands has taken place, extensive advances also preceded a twentieth century retreat in earlier centuries. An interesting and dynamic example of the general behavior of New Zealand glaciers is that of the Franz Josef glacier, whose impressive retreat (with occasional advances, like a 200 meter one in 1985) in the past century has been credited, with much debate and controversy, to increased temperature since the time of the Little Ice Age. Although information about the glaciers of the Southern Hemisphere during the 16th through 18th century is very scarce, it is certainly true that they have generally been on a recession since the 19th century, as the following pictures of the Franz Josef demonstrate. xxx

Glaciers in the Himalayas
Glaciers of Asia, as those in the Southern Hemisphere, are scarcely known, thus making conclusions about their movement in the past quite difficult to determine. In fact, of the first three IAHS/Unesco volumes published on the fluctuations of glaciers, "the first contained only European material, and even the third had data from only one Himalayan glacier" in spite of the fact that the area covered by ice in the Himalayas is thirty-three times greater than that of Europe's ice cover and is the largest ice covered region outside of the Arctic and Antarctic (Grove 199).
Evidence does exist, though, to support the belief that mountain glaciers there were greater during the European Ice Age than present. For example, there exist many Hindu temples near the glacial source of the Ganges River, which plays an important role in the Hindu religion. But these temples are now over 30km from the actual source of the Ganges that leads many to wonder that the glacier was much closer when these temples were initially built (Grove 207-209). More concrete evidence (tree ring studies and observations of Chinese glaciers in the 20th century) leads many to believe that temperatures throughout Asia were lower from the 14th century until the middle 19th century than present.
When looking at the areas of the Earth that is prone to glaciers, it is generally safe to say that around the world, many of the glaciers are presently holding recessed positions when compared to where they were during the Little Ice Age. Still, it is still not totally certain that this correlation is due to falling, then rising temperatures. One cannot forget the fact that glaciers like the Franz Josef in New Zealand may be contracting more due to a change in precipitin patterns over the past one hundred years that is totally independent of climatic changes elsewhere in the globe. There still remains sufficient evidence, nevertheless, that the European Little Ice Age was at least climatically important (albeit devastating) to places and people situated at polar extremes and mountainous regions where glacial and permafrost encroachment offers little or no alternative, as in the case of the Greenland Colony.

The factors of Climate change can be divided upon a scale of time and space. That is to say, in order to figure out what factors are most responsible for any particular Climate change, one must be sure to keep in mind the size the affected area (local, regional, global, extra-global) and the time over which the change occurred. In regards to the Little Ice Age, then, one must look for climatic influences that operate within a two to three hundred year cycle of this Age and were global in nature. But, to be sure not to close our scope too much, let us begin with the external variables, and ultimate (initial) determinants of climatic change on earth: the sun and the earth's relation to it.
The basic reason why the earth has Weather is because the energy it receives from the sun is not absorbed equally. winds, currents, and storms occur because of the transfer of the sun's energy from one place to another and/or from one form to another. Changes in the Weather pattern (i.e. Climate) can at length be a result of a change in the energy transfer relationship between the sun and the earth's atmosphere, land, and oceans. These external changes can be caused by fluctuations in the output of the sun, earth-sun geometry, and atmospheric chemistry. They differ from internal processes of the earth that involve feedbacks from one part of the climatic system to another, such as surface albedo and the atmosphere-ocean relationship (Adams 1-10).

Wavering sun
It is known that the sun's output and the earth's relationship to the sun are quite complicated to quantify. To begin with, the sun regularly fluctuates in intensity by about a fourth of a percent during an eleven-year cycle. But also, studies of other stars have shown that they can regularly go through extended quiet periods where a star's intensity fell by up to five percent for a number of years. These quiet periods are measured by observing the reduction in sun spot activity of a star. Of thirteen stars routinely measured since 1966, four have exhibited this extended 'flat' period throughout the Study (Gribbin 19). Not to mention the fact that our sun is constantly getting hotter, and thus affecting earth's Climate, it also has quite the potential (based on studies of other similar stars) to fluctuate its intensity over years, decades, and even centuries. It is believed that these fluctuations are a function of the sun's rotation. More specifically, "the rotation speed of the sun is inversely correlated with sunspot numbers" because an increased rotation "inhibits transport of the magnetic field from the Deep interior to the surface and could cause a reduction of solar wind" (Grove 366-367).
Support for sun fluctuations as the source of the Little Ice Age comes from a recorded decrease in sunspots during part of the Little Ice Age. As early as the 1880's, a German astronomer, Gustav Sporer, began wondering why it was that very few sunspots were seen in parts of the 17th and 18th century, even though there were "so many observers of the sun, as were then perpetually peeping in upon (it) with their telescopes in England, France, Germany and Italy" (Eddy 1976, in Grove 366). The prolonged absence of sunspots between 1645 and 1715 came to be known as the Mauder minimum. During this period, based on drawing of early astronomers, the sun's rotation was faster during the Little Ice Age than present, which accounts for the low numbers of sunspots. Still, the Mauder Minimum does not occur through the whole period of the Little Ice Age, thus making a definitive correlation problematic.

Earth-sun Geometry
As well, Earth's orbit around the sun is far from perfectly static. Rather, as Serbian astronomer Milutin Milankovitch hypothesized in the 20's and 30's, the earth's rotation around the sun and its tilt are subtly influenced by the gravitational forces of other planets and celestial bodies. The subtle changes, though, can "result in different distributions and intensities of sunlight, which then lead to dramatic variations in Climate over tens of thousands of years" (Alley 80). These dramatic variations are, in fact, the 100,000 year glacial-interglacial cycle (due to the eccentricity of earth's orbit), and the shorter-term 20,000 and 40,000 year cycles (due to the earth's angle of tilt and then the precision of this tilt, respectively). As a side note, we are presently on the tailend of an interglacial period; Milankovitch cycles, though, are on a much too large of time scale to explain the relatively short period of the Little Ice Age. The rest of climatic change variables can be grouped as internal changes on Earth. The four possible factors are volcanism, Greenhouse gases, surface albedo, and the ocean-atmosphere relationship.

It is well known that volcanic injection of micro-particles and gases into the stratosphere reduce the amount of solar energy that reaches the surface of the Earth. Successive volcanoes (or even one) can temporarily dust the sky of the entire Earth and thus affect the Climate of the Earth on a variety of time-scales. For example, the eruption of Mt. Agung in 1963 had a marked effect on the Climate of the American high Arctic as well as in the tropical troposphere, where temperature decreased almost one degree Celsius from August 1964 to August 1965. But other equally large eruptions, like Bezymyannyy in 1956, have not been followed by a similar decline in temperature, most likely due to difference like the location and chemical make-up of the eruption, which make simply equating more eruptions with lower temperatures a bit troublesome. Consequently, "there seems little doubt that volcanic activity influences Climate but the extent of this influence is controversial" (Grove 368).
Nevertheless, an ice-core from Crete, Greenland shows a rather provocative correlation between increased volcanic activity and lower than average temperatures over the past fourteen hundred years. In the following graph, lower-than-average acidic levels of the Greenland core (e), which refers to decreased amounts of sulfate in the atmosphere due to volcanic activity, matches almost perfectly with the warm periods of this era. (See graph). "The quietist period volcanically was from CE 1100 to 1250, that is in the medieval warm period. The most active period volcanically came between CE 1250 and 1500 and between CE 1550 and 1700, suggesting that it had an important role in the causation of the Little Ice Age" (Grove 376).

Surface Albedo
A very important amplifier to any glacial-like advance is the reflective effect of ice and snow. An increase in snow and ice reflects back larger amounts of solar energy, thus making surface temperatures even colder and therefore resulting in the possibility for even more snow and ice: a classic feedback situation. Given the fact that the amount of snow and ice can easily be increased or decreased given minor changes in temperature due to, for example, small changes in solar output or volcanism, surface albedo can become an intense resonator to further decreases in surface temperature (Adams 7).

Ocean-Atmosphere conveyor system
One of the most interesting and plausible factors for the Little Ice Age is the relationship between the ocean and the atmosphere. Both are huge sinks for energy and compounds; any change in their relationship "must have effects on the prevailing Climate" (Lamb 1). Possibly the most famous region for the ocean-atmosphere relationship is in the North Atlantic, where the tropical Gulf Stream brings warm currents and air far north to meet the cold Arctic waters off the coasts of Greenland, Iceland, and Norway. It is well known that the shutting off or slowing down of the Gulf Stream in the North Atlantic has amplified affects on the Climate of Europe because it is responsible for keeping the water and air around Europe (which is very far north) much warmer than its Latitude would imply.
Warm, tropical water is brought so far north because the movements of surface winds and surface currents follow each other. Air and Water are both fluid and therefore they tend to follow similar courses. " The general world map of ocean currents is very similar to the pattern of the prevailing winds that drive them. And when the wind-flow pattern is distorted by great meandering of the steering current aloft, ...the ocean current system must tend to be distorted as well" (Lamb 3). For example, an atmospheric low, which is by definition is cyclonic, will push air away from the air mass' center due to the correolis effect. These outward tending winds will also force ocean currents to diverge from the center as well. The opposite is true of an atmospheric high, where anti-cyclonic winds and currents will both diverge towards the center of the air mass.
This fact becomes extremely important with an air mass over the Atlantic because
an atmospheric low will make waters diverge towards the out rim of the Atlantic Basin, while an atmospheric high will cause water currents to converge towards the middle. It is well known that it is the divergent tendencies of the North Atlantic that keep the Gulf Stream powered and if an atmospheric high were to replace the usual atmospheric low over the North Atlantic, the currents would converge, thus greatly weakening the Gulf Stream. In fact, reconstruction of average pressure Maps from 1790 to 1829 by Hubert Lamb and Johnson reveal that there was far less cyclonic wind stress south of Iceland then during the 20th Century (Grove 360). It is therefore possible to assume that the deteriorating Climate of the Little Ice Age in Europe can be partly explained by the slowing of the Gulf Stream.
The question is then, did this happen elsewhere in one of our seven oceans? Surely this is not an isolated relationship, right? In reality, many feel that it is, for the following reasons.
The North Atlantic is quite unique, in regards to the ocean-atmosphere connection, for a number of reasons. Firstly, in comparison to the Pacific, it is far more saline. The enriched salinity of Atlantic surface water enable it be become dense enough, when cooled, to sink to the ocean floor. By contrast, the fresher waters of the Pacific, no matter how much they are cooled in relation to the Deep water, will never be dense enough to sink more than to an intermediate level. The sinking of Gulf Stream waters in the north Atlantic causes more warm water from the tropics to be 'pulled' north like a conveyor.
This warm water brought north brings vast amounts of energy to the Arctic maters and atmosphere. Wallace Broecker, Dorothy Peteet, and David Rind estimate the byproduct of this Deep water formation to be about 5* 1021 calories of heat that is released to the atmosphere: "an amount corresponding to ~30% of the solar heat reaching the surface of the Atlantic Ocean in the region north of 35° N" (Broecker 24).
Obviously, the salinity of the Atlantic is quite important to the transfer of energy (5* 1021 calories of heat) to the region around Europe. If the salinity were changed, then, the Deep-water formation of the Gulf Stream would be shut off or diminished. A number of possible hypothesis exist that account for this. For example, there is evidence that the water exchange between the Atlantic and Pacific in the Bering Strait was much greater 300 years ago than present (Lamb 5). Also, the salinity of the Atlantic ocean, as Adams and Maslin suggest, "a pulse of fresh river water (could) dilute the dense, salty Gulf Stream and float on top, forming a temporary lid..."(Adams5). Either of these two scenarios, in conjunction with the anti-cyclonic winds of the time could have lowered (1) the salinity of the Atlantic, (2) made Deep water production impossible, (3) and caused arctic ice to form further south. In the winter, with a lack of warm water in the North Atlantic the temperatures in Europe would be much more Severe Weather. And in the summer, ice formation would (4) make the air reaching Europe cooler and dryer because of an albedo effect and therefore (5) diminish glacial melting in the latitude and altitude extremes, causing glacial advance.
But, this scope of ocean-atmosphere effects on Climate (i.e., just the north Atlantic) does not fully explain why there were glacial advances, due to decreased temperature, throughout the world during the Little Ice Age. As Broecker points out, "we may be dealing with a regional change in Climate involving primarily the area under the climatic influence of the northern Atlantic Ocean." To explain global cooling, one must consider the evidence for diminished sunspots and increased volcanism during this time. As well, Broecker adds, "Evidence for such an oscillation (like the Deep water circulation in the North Atlantic) has been found elsewhere, that is, in the cordillera of South America and in New Zealand...(T)he situation may well be more complicated" (Broecker 24). Unfortunately, there is little historical data on ocean temperature in any other region other than the North Atlantic. But as Broecker points out, if the reasons why the Little Ice Age had global implications are to be found, the North Atlantic conveyor belt may only explain Climate change in the area around Europe. One must not drunkenly 'look under the street light', as the saying goes, when what is being looked for is in fact on the other, unlit curve.
The global implications of the Little Ice Age are still debatable, but it is rather safe to say that for a variety of reasons, the world was cooler for a period of time. And although the Little Ice Age devastated those who were sustaining themselves at a latitude and altitude extreme, it is important to keep in mind that this 'ice age' was a tiny blip in the climatic fluctuations of earth. By far, other climatic fluctuations in even the Holocene, like Younger Drias which last over 800 years, have been far more intense and last much longer. Determining the reasons for the Little Ice Age is quite a challenge. Ult

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