Summary

The Little Ice Age was a period of relatively cool climate from the beginning of the 15th century until the 19th century. It varied in intensity regionally and temporally. Only during a core period, from the end of the 16th century to the last third of the 17th century, can a cooler phase be identified globally.

The Little Ice Age is part of recent climate history and the subject of research in historical climatology. In today's climate discussion, it is considered the classic example of a natural climate variation characterized by short-term fluctuations.

The Little Ice Age was preceded by a period known as the Medieval Warm Period. The beginning of the Little Ice Age is often given as the middle of the 15th century, from which time onward cooler conditions occurred regionally and temporally in varying degrees. A globally cooler phase cannot be identified until a later period, from the end of the 16th century to the last quarter of the 17th century. Even in this core period of the Little Ice Age, there was still considerable variability: In the Northern Hemisphere, the periods from about 1570 to 1630 and 1675 to 1715 were particularly cold. In the Southern Hemisphere, the core period was from shortly after the beginning until the second half of the 17th century Regionally and temporally weighted differently, temperatures during the Little Ice Age were about 0.1 Kelvin (K) lower worldwide in the period 1400-1800 than during the preceding centuries 1000-1400. Over shorter periods of a few decades, temperatures may have been as much as 0.8 K lower, and in some European regions 1 to 2 K lower.

During the Little Ice Age, very cold, long winters and cool summers with high precipitation frequently occurred. In the middle of the 17th century and also until the middle of the 19th century, glaciers advanced twice in the Alps, destroying homesteads and villages. Glacier growth during the Little Ice Age was the strongest since the long-lasting glaciation of the last ice age.

Various historical accounts and events are associated with the Little Ice Age and used to illustrate it:

The Great Famine in Ireland in 1845-1852, for example, is seen as the last marker of the Little Ice Age. The rise in mean temperatures is distorted by the year without a summer (caused by the eruption of the Tambora volcano on the island of Sumbawa, east of Java, in 1815.

From about 1850, the world became warmer; this is considered the end of the Little Ice Age. Since then, global average ground temperatures have risen by about 1 K and are thus probably warmer (based on a period of 50 years) than they have been for at least 1300 years.

Since the mid-19th century, a significant retreat of glaciers has been observed almost worldwide (see Glacier retreat since 1850).

The Little Ice Age is evidenced in many natural climate archives by a number of proxies (indirect climate data), such as:

Some paintings from that time can also be used as indicators of past climatic conditions. Well known for this are, for example, the depictions of winter landscapes by Pieter Brueghel, Hendrick Avercamps and other Dutch masters from the 16th and 17th centuries. Many of them show scenes depicting frozen canals in the Netherlands. Vivaldi's Winter Concerto with its accompanying sonnet, for example, takes as its theme skating on the Venice Lagoon. From the 19th century on, this period was over, the (average) temperatures have been higher since then, and there were fewer observations that, for example, the aforementioned canals or Venice's lagoon were frozen.

Paintings of the early Manchurian Qing dynasty (from 1644) show snowy landscapes. The collapse of the preceding Ming dynasty was helped by crop failures due to repeated droughts beginning in the 16th century, and especially an extreme drought in 1638-1641. The droughts occurred due to changes in the monsoon during a cold period documented in chronicles, possibly caused by volcanic eruptions. Comparable droughts have occurred again only since the second half of the 20th century.

When the first evidence of the Little Ice Age became apparent, it was assumed to be a worldwide climatic phenomenon. Today, this is partly seen differently. In order to obtain reliable data worldwide, hundreds of scientists have traveled to all continents since the 1990s in several national and international collaborative projects and compiled thousands of observations and proxy data there.

From different climate archives cooler periods could be proven on the northern and southern hemisphere, i.e. on all continents and both polar caps. Periods of significantly cooler climate were, however, distributed unevenly regionally and temporally. At least for a main phase of the Little Ice Age from the end of the 16th to the 19th century one can speak of a Northern Hemisphere phenomenon with an average deviation of summer temperatures of -0.5 K compared to the reference period 1960 to 1991. However, particularly low temperatures did not occur globally simultaneously over a period of more than a few decades. Significantly cooler phases with temperature deviations of more than 0.8 K in summer occurred in the 17th century in Northwest Asia and at the beginning of the 19th century in North Asia. A cold spell in China is documented for the period around 1650 (transition from the Ming to the Qing dynasty). In Greenland, there were particularly cool periods in the 14th, 15th, 17th, and first half of the 19th centuries. In Europe, it was significantly cooler at the time of the late Maundian Minimum, late 17th century, in Eastern Europe by up to 1.2 K. However, cooler average temperatures were also very unevenly distributed in Europe at this time, and a slight warming was also reconstructed in northern Scandinavia.

Increased volcanism, reduced solar activity, and reforestation of agricultural land after a population decline due to disease have been considered as causes of the Little Ice Age. Ocean currents altered by cooling are thought to have played a reinforcing role. In addition to these short-lived influences, there was a cooling trend beginning in the late Atlantic about 6000 years ago and lasting for millennia, caused by gradual changes in the Earth's orbit.

Increased volcanic activity

The Little Ice Age was preceded by a series of powerful volcanic eruptions, Plinian eruptions, which spewed dust and ash as well as gases, including sulfur dioxide (SO2), high into the Earth's atmosphere.

Through studies of today's volcanic eruptions, the processes taking place in the higher atmosphere, the stratosphere, are known. Volcanic solids and gases can remain there for several years and affect the climate. The sulfur dioxide is converted to sulfuric acid (H2SO4) in a photochemical reaction. The acid becomes a cloud of aerosol in the stratosphere, droplets suspended in the air that absorbs solar radiation and reduces insolation. In the shadow of the aerosol cloud, the lower atmosphere, the troposphere, cools.

In a study published in 2011, climate models were used to recreate the response of the global climate to a series of volcanic eruptions from the end of the 13th century onwards, as evidenced by ice cores. It was shown that a resulting rapid and strong cooling persists for many years through feedback processes such as ice-albedo feedback, long after the causative aerosols have disappeared from the atmosphere. Large changes in solar activity are not necessary for such a climate response. By examining the date of death of fossil plants on Baffin Island in the Canadian Arctic, the years from 1275 to 1300 and 1430 to 1455 turned out to be periods of relatively sudden death of vegetation and increased glacier growth evidenced by it.

The end of the Little Ice Age was marked by a series of significant volcanic eruptions. The eruption of the Laki craters in Iceland in 1783 caused the harsh winter of 1783

Reduced solar radiation

The annual output of solar radiation, the energy source of the Earth's climate, varies with solar activity on the order of 0.1%. Phases of lower solar activity are accompanied by lower radiation output and have a cooling effect on the Earth's climate. On the basis of the observation of sunspots, the solar activity can be reconstructed back to the year 1610. For the period before that, the solar activity can be approximated on the basis of the measurement of radioisotopes, which are produced by cosmic radiation penetrating the earth's atmosphere more frequently during periods of weaker solar activity (cosmogenic radioisotopes 14C and 10Be as proxy).

Phases of particularly low solar activity fall within the period of the Little Ice Age. The second half of a particularly cool phase of the Little Ice Age in the Northern Hemisphere, which began before 1600 and lasted until about 1710, coincides with the Maunder Minimum. During this period, from 1645 to 1715, the Sun exhibited a minimum of sunspots, which was accompanied by a somewhat reduced intensity of radiation. Even a slight attenuation can lead to significant cooling phenomena regionally. The Spörermimum, around 1420 to 1550, and the much shorter and less pronounced Dalton Minimum, around 1800, also fall within the Little Ice Age.

Globally, however, according to recent work, the changes in solar activity can only have been accompanied by comparatively small changes in radiant power. Thus, weaker solar activity is unlikely to have been a major cause of the Little Ice Age in the 16th and 17th centuries. Resulting temperature changes are estimated to be less than 0.3 K globally, with a most probable value of about 0.1 K. However, a much stronger regional influence, especially in mid-latitudes of the Northern Hemisphere, for example indirectly via an influence on the winter North Atlantic Oscillation and thus on the climate in Europe, is possible.

Reforestation due to population decline

In 2003, the paleoclimatologist William F. Ruddiman proposed the hypothesis that massive population decline could have led to reforestation. This would have sequestered enough carbon from the air to trigger the Little Ice Age through the resulting reduction in CO2 concentrations (→ Ruddiman hypothesis). Ruddiman specifically suspects the plague epidemics of the late Middle Ages as the trigger. It was also suspected that the massive population decline on the American continents, triggered by diseases introduced by Europeans, exacerbated the previously mentioned causes. After the population in the Americas was decimated by about 95%, large areas of previously fire-cleared farmland were reforested, which is estimated to have sequestered 2 to 5 gigatons of carbon from the atmosphere. This is equivalent to about 4 to 14% of a 7 ppm decline in CO2 concentrations that occurred during the period 1550-1750. The resulting reduced greenhouse effect would have led to the 0.1 K cooler period over the period.

However, the decline in fires in the Americas began as early as 1350, and the greatest decline in burned biomass was located precisely in regions of the Americas with low population density and late contact with Europeans. Found charcoal remains, on the other hand, correlate well with the temporally and spatially inconsistent climate fluctuations of the Little Ice Age. From this, other authors conclude that local climate fluctuations, rather than population decline, were the main cause of reforestation. Overall, there is no high correlation between fires and CO2 concentrations globally during the Holocene. According to other researchers, the decline in CO2 concentrations is rather explained by CO2 uptake in peatlands and deposition of calcium carbonate in shallow waters.

Weaker Gulf Stream

According to studies by Jean Lynch-Stiglitz and her colleagues, the Gulf Stream was about 10% weaker than usual at the time of the Little Ice Age. The basis for the calculation was the 18O

Changes in the orbit of the Earth around the Sun

Beginning about 6000 years ago, there was a long-term cooling trend of slightly more than 0.1 K per millennium until the 19th century - especially in the middle and high latitudes of the Northern Hemisphere. According to climate simulations, this cooling trend is due to changes in the Earth's motion relative to the Sun, primarily a change in the tilt of the Earth's axis. This changes the seasonal and regional distribution of solar radiation reaching the Earth. Such changes in solar radiation can alter snow and ice cover and vegetation in mid- and high northern latitudes, triggering climatic feedbacks such as an ice-albedo feedback that lead to long-term cooling, especially in the north.

hardship, social tensions, persecution of minorities

Weather and climate fluctuations are seen, especially by British and Scandinavian researchers, as a trigger for late medieval agricultural crises in the 14th and 15th centuries in Europe. Individual authors, such as Hubert Lamb, see the crisis in a transitional period from a medieval warm period to a little ice age, which they thus start early. Due to deep and long winters, vegetation periods were reduced. Summers were cold and wet, so that wheat, for example, rotted on the stalks. Food production declined, and famine occurred. Wolfgang Behringer pointed out that during this period, there were frequent famines, malnutrition and epidemics, which ultimately exacerbated social tensions among the population.

Social minorities and marginalized groups were repeatedly blamed for crop failures. Falling yields were often seen as the result of black magic. The period of the Little Ice Age saw both the early modern persecution of witches in Central Europe and the increased persecution of social minorities (especially Jews and smaller Christian denominations such as the Anabaptists). In many witch trials, the defendants were accused, among other things, of damaging weather (e.g., frost in wine-growing areas and hail).

Power political events

The Little Ice Age shaped an epoch of significant historical events in Europe and beyond. The knowledge about the climatic problems would lead to a clearer picture of that time. To what extent these problems not only aggravated the living conditions at that time, but also contributed causally to the major conflicts, historical research will also have to clarify. Wolfgang Behringer suspects, among other things, a connection between the social unrest triggered by the climatic changes and the expansion of the early modern state. The outbreak of the Thirty Years' War and - much later - the French Revolution, for example, provide grounds for consideration of exogenous causes.

After the population in the German lands almost doubled from 1500 to 1618, and when temperatures began to drop steadily from about 1570, a catastrophic situation arose for the people in the country, which manifested itself in despair, mistrust and a doomsday mood. Several bad harvests, hurricanes and harsh winters are known from the period between 1560 and 1610. These grievances prepared an upheaval in society and are considered - among other circumstances - a breeding ground for wars in the first half of the 17th century, such as the Thirty Years' War.

In pre-revolutionary France, there was an increase in population from about 1770, which was not matched by a sufficient increase in food production. The subsequent rise in food prices was compounded by an economic crisis that was exacerbated by misguided policies. The years 1787 and 1788 were therefore marked by the simultaneity of an agricultural, industrial and social crisis.

This situation was compounded in 1788 and 1789 by one of the accumulations of climatic extremes characteristic of the Little Ice Age. In 1788, as a result of an extreme drought and a severe hailstorm, grain yields in France fell by over 20 percent compared with the average of the previous ten years. This caused prices to rise more than a year before the French Revolution. Following the extremely cold winter of 1788

Consequences of advancing pack ice

During the Medieval Warm Period, among other things, the pack ice in the northern Atlantic had retreated northward and some land glaciers had disappeared. This warming allowed the Vikings to settle Iceland (from about 870) and coastal areas of Greenland (from 986).

As a result of the cooling, the pack-ice boundary advanced southward again in the 15th century and from about 1700 until the 19th century, interrupted by a period of particularly low ice extent. The advancing pack ice temporarily isolated Iceland from the outside world, causing a sharp decline in population. Climatic deterioration is considered a possible reason why, in the 16th century, the Scandinavian colony on Greenland, to which about 3,000 people had belonged around 1300, became extinct.

Sources

1. Little Ice Age
2. Kleine Eiszeit
3. ^ Hawkins, Ed (30 January 2020). "2019 years". climate-lab-book.ac.uk. Archived from the original on 2 February 2020. ("The data show that the modern period is very different to what occurred in the past. The often quoted Medieval Warm Period and Little Ice Age are real phenomena, but small compared to the recent changes.")
4. ^ a b c "Climate Change 2001: The Scientific Basis". UNEP/GRID-Arendal. Archived from the original on 29 May 2006. Retrieved 2 August 2007.
5. a b c Raphael Neukom u. a.: Inter-hemispheric temperature variability over the past millennium. In: Nature Climate Change. März 2014, doi:10.1038/NCLIMATE2174.
6. a b Mathew J. Owens, Mike Lockwood, Ed Hawkins, Ilya Usoskin, Gareth S. Jones, Luke Barnard, Andrew Schurer und John Fasullo: The Maunder Minimum and the Little Ice Age: an update from recent reconstructions and climate simulations. In: Journal of Space Weather and Space Climate. Band 7, A33, 2017, doi:10.1051/swsc/2017034.
7. Le mot « âge » ne prend pas de majuscule quand il désigne une période de l'histoire, sauf pour le Moyen Âge : l'âge de la pierre, l'âge du fer, l'âge du bronze, etc.
8. a b c d e Lunkka, Juha Pekka: Maapallon ilmastohistoria, s. 248–249. Gaudeamus, 2008. ISBN 978-952-495-083-1.
9. Alan D. Wanamaker, Paul G. Butler, James D. Scourse, Jan Heinemeier, Jón Eiríksson, Karen Luise Knudsen: Surface changes in the North Atlantic meridional overturning circulation during the last millennium. Nature Communications, tammikuu 2012, nro 3, s. 899. PubMed:22692542. doi:10.1038/ncomms1901. Artikkelin verkkoversio. (englanniksi)