History/Recent/Little Ice Age
The Little Ice Age (LIA) appears to have lasted from about 1218 (782 b2k) to about 1878 (122 b2k).
A "climate interpretation was supported by very low δ’s in the 1690’es, a period described as extremely cold in the Icelandic annals. In 1695 Iceland was completely surrounded by sea ice, and according to other sources the sea ice reached half way to the Faeroe Islands."
In the image at the top, "before present" is used in the context of radiocarbon dating, where the "present" has been fixed at 1950. The apparent decreases in solar activity are called the "Maunder Minimum", "Spörer Minimum", "Wolf Minimum", and "Oort Minimum".
"Northern Hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes."
Precisely "dated records of ice-cap growth from Arctic Canada and Iceland [show] that LIA summer cold and ice growth began abruptly between 1275 and 1300 AD, followed by a substantial intensification 1430-1455 AD. Intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium. [Explosive] volcanism produces abrupt summer cooling at these times, and that cold summers can be maintained by sea-ice/ocean feedbacks long after volcanic aerosols are removed. [The] onset of the LIA can be linked to an unusual 50-year-long episode with four large sulfur-rich explosive eruptions, each with global sulfate loading >60 Tg. The persistence of cold summers is best explained by consequent sea-ice/ocean feedbacks during a hemispheric summer insolation minimum; large changes in solar irradiance are not required."
"As shown in the figure [on the right], there is a paucity of sunspots during 1645-1715 and, to a lesser extent, again during 1800-1840. These intervals of low sunspot numbers are known as the Maunder Sunspot Minimum and Dalton Sunspot Minimum, respectively."
The cycle of the seasons fascinated 17th-century Europeans, but the shifts in the tilt of the earth that causes them were not understood. Winter was especially hard then; Europe was in the middle of a little ice age and it was much colder than today. The Southern Netherlands was also in the midst of a war, and ill-paid soldiers terrorized the peasants. Here, on the right, the landscapist de Momper uses subdued color and tonal unity to suggest the bleakness of a late winter afternoon, complemented by an intricate, stark pattern of barren branches against the sky.
"The Maunder Minimum, which occurred during 1645-1715, was an interval of low sunspot numbers and greatly diminished solar-induced activity like aurorae and solar winds. This period of very low solar activity, and an inferred, earlier solar activity minimum (1450-1550) known as the Spörer Minimum roughly coincided with cooler climates in Europe and Asia known as the Little Ice Age."
The solar cycle has a great influence on space weather, and a significant influence on the Earth's climate since the Sun's luminosity has a direct relationship with magnetic activity. Solar activity minima tend to be correlated with colder temperatures, and longer than average solar cycles tend to be correlated with hotter temperatures. In the 17th century, the solar cycle appeared to have stopped entirely for several decades; few sunspots were observed during this period. During this era, known as the Maunder minimum or Little Ice Age, Europe experienced unusually cold temperatures. Earlier extended minima have been discovered through analysis of tree rings and appear to have coincided with lower-than-average global temperatures.
"MOST current literature on solar activity assumes that the planets do not affect it, and that conditions internal to the Sun are primarily responsible for the solar cycle. Bigg1, however, has shown that the period of Mercury's orbit appears in the sunspot data, and that the influence of Mercury depends on the phases of Venus, Earth, and Jupiter."
"It is shown that starting with the alignment of Venus with Jupiter at perihelion position, these two planets will perfectly align at Jupiter's perihelion after every 23.7 years".
"The tidal forces hypothesis for solar cycles has been proposed by Wood (1972) and others. Table 2 below shows the relative tidal forces of the planets on the sun. Jupiter, Venus, Earth and Mercury are called the "tidal planets" because they are the most significant. According to Wood, the especially good alignments of J-V-E with the sun which occur about every 11 years are the cause of the sunspot cycle. He has shown that the sunspot cycle is synchronous with the alignments, and J. Schove's data for 1500 year of sunspot maxima supports the 11.07 year J-V-E period average."
"Both the 11.86 year Jupiter tropical period (time between perihelion's or closest approaches to the sun and the 9.93 year J-S alignment periods are found in sunspot spectral analysis. Unfortunately direct calculations of the tidal forces of all planets does not support the occurrence of the dominant 11.07 year cycle. Instead, the 11.86 year period of Jupiter's perihelion dominates the results. This has caused problems for several researchers in this field."
"[B]y assuming a harmonic variation having a period of 11.13 years ... the phases of such a variation [in polar diameter minus equatorial diameter of the Sun] coincide to within one-fifth of a year with the phases of the sun-spot fluctuations; that, at times corresponding to minimum of sun-spottedness, the polar diameter is relatively larger; that, at times of maximum sun-spottedness, the equatorial diameter is relatively larger. The amplitude of the variation is extremely small, but its reality would seem to be established. [This] at least renders the existence of such periodic fluctuations in the shape of the sun more probable than their non-existence."
"Solar oblateness, the difference between the equatorial and polar diameters, reflects certain fundamental properties of the Sun. ... the oblateness reflects properties of the Sun's interior, ... [There is] a time varying, excess equatorial brightness [producing] a difference between the equatorial and polar limb darkening functions ... at times when the excess brightness is reduced, the intrinsic visual oblateness can be obtained from the observations without detailed knowledge of the excess brightness. A period of reduced excess brightness occurred in 1973 September." The period of reduced excess equatorial brightness occurred between solar cycle maximum around 1970 and minimum around 1975. Considering excess equatorial brightness and seeking to perform measurements at opportunities of reduced excess equatorial brightness has the effect of reducing solar oblateness from some 86.6 ± 6.6 milli-arcsec to 18.4 ± 12.5 milli-arcsec.
The Babcock Model describes a mechanism which can explain magnetic and sunspot patterns observed on the Sun.
- The start of the 22-year cycle begins with a well-established dipole field component aligned along the solar rotational axis. The field lines tend to be held by the highly conductive solar plasma of the solar surface.
- The solar surface plasma rotation rate is different at different latitudes, and the rotation rate is 20 percent faster at the equator than at the poles (one rotation every 27 days). Consequently, the magnetic field lines are wrapped by 20 percent every 27 days.
- After many rotations, the field lines become highly twisted and bundled, increasing their intensity, and the resulting buoyancy lifts the bundle to the solar surface, forming a bipolar field that appears as two spots, being kinks in the field lines.
- The sunspots result from the strong local magnetic fields in the solar surface that exclude the light-emitting solar plasma and appear as darkened spots on the solar surface.
- The leading spot of the bipolar field has the same polarity as the solar hemisphere, and the trailing spot is of opposite polarity. The leading spot of the bipolar field tends to migrate towards the equator, while the trailing spot of opposite polarity migrates towards the solar pole of the respective hemisphere with a resultant reduction of the solar dipole moment. This process of sunspot formation and migration continues until the solar dipole field reverses (after about 11 years).
- The solar dipole field, through similar processes, reverses again at the end of the 22-year cycle.
- The magnetic field of the spot at the equator sometimes weakens, allowing an influx of coronal plasma that increases the internal pressure and forms a magnetic bubble which may burst and produce an ejection of coronal mass, leaving a coronal hole with open field lines. Such a coronal mass ejections are a source of the high-speed solar wind.
- The fluctuations in the bundled fields convert magnetic field energy into plasma heating, producing emission of electromagnetic radiation as intense ultraviolet (UV) and X-rays.
Solar activity proxies
"Some of the [solar activity] proxies used [to extend the time base back nearly 2000 years] are historical records of naked-eye sunspot sightings, occurrence of aurorae, and 14C variations measured from tree ring analyses. The ratio of isotopic 14C to 12C is a good measure for solar activity. Less 14C is produced in the upper atmosphere when the Sun is active because of the blocking action of the denser solar wind to galactic cosmic rays."
"In 1716, for virtually the first time, the Royal Society and the Académie des Sciences carried articles on the aurora borealis in their journals. Both societies were then a half century old. However, merely 34 years later the Philosophical Transactions had recorded 200 observations of aurorae, and the Mémoires de l'Académie a similar number. The reason for the late and simultaneous debut was the return of the aurora to the latitudes of London and Paris, in or near which most of the societies' members lived."
"The auroral events of the year 1716 most clearly announced that the prolonged solar and auroral calm that we now call the Maunder Minimum [Eddy, 1976a] had ended. But the onset of renewed auroral activity was noted already in the previous solar cycle. In 1707 an aurora was seen in Berlin and recorded in the journal of the Berlin Academy. Curiously, in New England, which is closer to the auroral zone than is London, Paris, or Berlin, the aurora returned suddenly in 1719. Contemporary accounts put the first recorded appearance of an aurora in Italy in the 1720's."
"By the time that Jean Jacques Dorious de Mairan published his landmark treatise on the aurora in 1733, he had accumulated a sufficient record to draw two important conclusions: the auroral occurrence frequency had increased suddenly in 1716 and had remained essentially constant since then, and there were a number of times in the past when auroral occurrences had resumed after long absence [de Mairan, 1733]. He identified 22 such instances in the interval 500 A.D. to 1731 and referred to them as resuptious (reprises)."
The "aurora again went into decline for a period of about 33 years, between 1792 and 1826, at a time when careful, routine observations of it were being made in Europe and America."
"Investigation of secular variations prior to the Maunder Minimum is now possible based on six auroral catalogs that have been published within the last 20 years. The catalogs cover the time period from the fifth century B.C. to the seventeenth century A.D. and combine both oriental and European observations. Features corresponding to the previously recognized Medieval Minimum, Medieval Maximum, and the Spörer Minimum are clearly evident in both oriental and European records. The global synchronicity of anomalies in the auroral occurrence frequency is used to argue that they are caused by changes in the level or state of solar activity.The combined catalogs provide a sufficient number of events in the Middle Ages to resolve aquasi-80-year periodicity in the recorded auroral occurrence frequency. Also in the unusually rich intervals of the Middle Ages, clear quasi-10-year periodicities appear in the recorded occurrence frequency waveform. These are most reasonably interpreted as manifestations of the 11-year solar cycle and indicate that the solar cycle was then operative."
North Sea continental shelves
"The populated 1.0 km² main island (Hauptinsel) to the west and the Düne to the east, which is somewhat smaller at 0.7 km², as well as lower, and surrounded by sand beaches. They were connected until 1720, when the natural connection was destroyed by a storm flood."
witt Kliff (white cliff) was a small chalk rock east of Helgoland until the early 18th century, when it was eroded to below sea level.
Greenland ice cores
To investigate the possibility of climatic cooling, scientists drilled into the Greenland ice caps to obtain core samples. The oxygen isotopes from the ice caps suggested that the Medieval Warm Period had caused a relatively milder climate in Greenland, lasting from roughly 800 to 1200. However, from 1300 or so the climate began to cool. By 1420, we know that the "Little Ice Age" had reached intense levels in Greenland.
"In 1974, [in central Greenland (71°7’N 37°19’W)] thermo-drilling [7.6 cm diameter core] took place at Crête in the coldest area of the inland ice (annual mean surface temperature -32 ̊C). The mean accumulation rate 28 cm of ice per year was marginal for the survival of the annual δ-cycles [image at the right], but a model was developed for the diffusion re-establishing the almost obliterated cycles – we called the technique for “reversed diffusion” [ref. 8.1]. Annual cycle counting showed that the oldest layer in the 404 m long core was deposited in A.D. 534."
"The Crête core was drilled in central Greenland (1974) and reached a depth of 404.64 meters, extending back only about fifteen centuries.
In the diagram at the right β-radiation in dose per hour (dph) and δ measurements along the upper 16 m of the Crête core from 1974 are aligned to depth.
"The seasonal cycles in the δ curve to the right have decreasing amplitude downward, because the diffusion in the porous firn tends toward elimination of all δ-gradients. However, the cycles are distinct enough for exact dating back to 1942. The grey shaded curve shows the specific β-radioactivity profile: There is no trace of fall-out from the nuclear bombs in 1945, but the first hydrogen bombs in 1953-55 caused considerable radioactive fall-out on the inland ice, and so did the test series in 1958-59 and in the early 1960’es."
"The Crête 1984 ice cores consist of 8 short cores drilled in the 1984-85 field season as part of the post-GISP campaigns. Glaciological investigations were carried out in the field at eight core sites (A-H)."
The second diagram at the right "shows the mean acidity of each of the 1440 annual layers in the Crête core identified by the δ-method [...]. Many known, and far more unknown volcanic eruptions in the northern hemisphere are revealed in this record. Observe that the acidity does not directly indicate the magnitude of eruptions. Those in low latitudes do not appear so strongly as similar eruption in the nearby Iceland. Notice in [the diagram] the moderate volcanic activity in the medieval period 850 to 1250 and in the 20’th century, both warm periods, and the intense volcanic activity in “The Little Ice Age” 1350-1700."
Upper Fremont Glacier
Ice core samples were taken from Upper Fremont Glacier in 1990-1991. These ice cores were analyzed for climatic changes as well as alterations of atmospheric chemicals. In 1998 an unbroken ice core sample of 164 m was taken from the glacier and subsequent analysis of the ice showed an abrupt change in the oxygen isotope ratio oxygen-18 to oxygen-16 in conjunction with the end of the Little Ice Age, a period of cooler global temperatures between the years 1550 and 1850. A linkage was established with a similar ice core study on the Quelccaya Ice Cap in Peru. This demonstrated the same changes in the oxygen isotope ratio during the same period.
An ice core has been analyzed, as shown on the right, for mercury over the last 270 years.
The image on the right shows the retreat of the Little Ice Age glacier.
"Lateral and terminal moraines of a valley glacier, Bylot Island, Canada [are shown in the image at the left]. The glacier formed a massive sharp-crested lateral moraine at the maximum of its expansion during the Little Ice Age. The more rounded terminal moraine at the front consists of medial moraines that were created by the junction of tributary glaciers upstream."
Def. "a mound, ridge, or other distinct accumulation of glacial till" is called a moraine.
Def. "a ridge-shaped moraine deposited at the side of a glacier and composed of material eroded from the valley walls by the moving glacier" is called a lateral moraine.
Def. "a ridge-shaped moraine deposited at the [terminus] of a glacier and composed of material eroded from the valley walls by the moving glacier" is called a terminal moraine.
"Good agreement is seen between the 14C (Fig. 8a) and 10Be (Fig. 8b) records, which confirms they are indeed measuring changes of the GCR flux, since their respective transport processes from the atmosphere to archive are completely different. After its formation, 14C is rapidly oxidised to 14CO2 and then enters the carbon cycle and may reach a tree-ring archive. On the other hand, 10Be attaches to aerosols and eventually settles as rain or snow, where it may become embedded in a stable ice-sheet archive. The correlation between high GCR flux and cold North Atlantic temperatures embraces the Little Ice Age, which is seen not as an isolated phenomenon but rather as the most recent of around ten such events during the Holocene. This suggests that the Sun may spend a substantial fraction of time in a magnetically-quiet state."
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- Ice-core evidence of rapid climate shift during the termination of the Little Ice Age - Upper Fremont Glacier study