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Scientists discover ‘surprising’ cause of Europe’s little ice age in late medieval era


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  • Location: Wonson, Throwleigh 845' ASL
  • Weather Preferences: winter
  • Location: Wonson, Throwleigh 845' ASL

    Following an era known as the medieval warm period, temperatures in Europe in the early 15th century fell sharply in what has become known as the little ice age

    This remarkable cold period brought increased glaciation in mountains, expansion of some areas of sea ice, crop failures, famines and disease across Europe.

    Undependable summers were followed by harsh winters, during which rivers and canals routinely froze over. In the UK, the first River Thames “frost fair” was held in 1608, and was an almost annual occurrence until the last one in 1814.

    The little ice age was not believed to have been due to a global period of glaciation, but its exact cause has remained uncertain.

    There are numerous explanations, including heightened levels of volcanic activity, reduced solar activity, the impact of the black death reducing the human population, and the impact of European diseases on South American populations, which in turn affected deforestation and reforestation rates.

    But scientists at the University of Massachusetts now believe they have found a new key factor in why temperatures plunged to their coldest in 10,000 years.

    “Surprisingly, the cooling appears to have been triggered by an unusually warm episode,” the researchers said.

    The discovery came after Lead author Francois Lapointe, a postdoctoral researcher and lecturer in geosciences at the University of Massachusetts, and Raymond Bradley, distinguished professor in geosciences, also at the University of Massachusetts, came across new data suggesting a rapid change in sea temperatures.

    Their previous work, which built a 3,000-year reconstruction of North Atlantic sea surface temperatures, revealed a sudden change from very warm conditions in the late 1300s to unprecedented cold conditions in the early 1400s, only 20 years later.

    Using various sources to obtain detailed marine records, Dr Lapointe and Professor Bradley discovered there had been an abnormally strong northward transfer of warm water in the late 1300s which peaked around 1380.

    As a result, the waters south of Greenland and the Nordic Seas became much warmer than usual.

    “No one has recognised this before,” said Dr Lapointe.

    The researchers said that usually there is always a transfer of warm water from the tropics to the arctic.

    It’s a well-recognised process called the Atlantic Meridional Overturning Circulation (AMOC), which is like a planetary conveyor belt.

    When it is functioning normally, warm water from the tropics flows north along the coast of Northern Europe, and when it reaches higher latitudes and meets colder arctic waters, it loses heat and becomes denser, causing the water to sink at the bottom of the ocean.

    This deep-water formation then flows south along the coast of North America and continues on to circulate around the world.

    But in the late 1300s, the AMOC strengthened significantly, which meant that far more warm water than usual was moving north, which in turn caused rapid arctic ice loss.

    Over the course of a few decades in the late 1300s and 1400s, vast amounts of ice were flushed out into the North Atlantic. This additional ice not only cooled the North Atlantic waters, but also diluted their saltiness, ultimately causing AMOC to collapse. It is this collapse of the conveyor belt which triggered substantial cooling, the researchers said.

    Furthermore, a similar process could now be underway.

    Between the 1960s and 1980s, we have also seen a rapid strengthening of AMOC, which has been linked with persistently high pressure in the atmosphere over Greenland.

    Dr Lapointe and Professor Bradley believe the same atmospheric situation occurred just prior to the little ice age – but what could have set off that persistent high-pressure event in the 1380s? The answer, Dr Lapointe suggested, can be found in trees.

    The researchers compared their findings to a new record of solar activity revealed by radiocarbon isotopes preserved in tree rings, and discovered that unusually high solar activity was recorded in the late 1300s.

    They said such solar activity tends to lead to high atmospheric pressure over Greenland.

    At the same time, fewer volcanic eruptions were happening on earth, which means that there was less ash in the air. A “cleaner” atmosphere meant that the planet was more responsive to changes in solar output.

    “Hence the effect of high solar activity on the atmospheric circulation in the North-Atlantic was particularly strong,” said Dr Lapointe.

    On the question of whether a second little ice age could now emerge, Dr Lapointe and Professor Bradley said there is now much less arctic sea ice due to the climate crisis, so an event like that in the early 1400s, involving sea ice transport, is unlikely.

    “However, we do have to keep an eye on the build-up of freshwater in the Beaufort Sea (north of Alaska) which has increased by 40 per cent in the past two decades,“ said Dr Lapointe.

    ”Its export to the subpolar North Atlantic could have a strong impact on oceanic circulation. Also, persistent periods of high pressure over Greenland in summer have been much more frequent over the past decade and are linked with record-breaking ice melt.

    “Climate models do not capture these events reliably and so we may be underestimating future ice loss from the ice sheet, with more freshwater entering the North Atlantic, potentially leading to a weakening or collapse of the AMOC.”

    The authors said there is now ”an urgent need“ for further research to address these uncertainties.

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    Posted
  • Location: Wonson, Throwleigh 845' ASL
  • Weather Preferences: winter
  • Location: Wonson, Throwleigh 845' ASL

    Further to the above, the relationship between increased Volcanic activity and the Little Ice age.

    Four huge volcanic eruptions triggered a 'Little Ice Age' that cooled earth for hundreds of years until the late 19th century, say scientists.

    The period of cooling led to famous events such as people ice skating on the River Thames.

    A study at the University of Colorado analysed sediment cores, vegetation and ice, and revealed that four massive tropical volcanic eruptions between 1275 and 1300AD triggered the period of cooling.

    Scientist Gifford collects vegetation samples on Baffin Island. The scientists analysed sediment, vegetation and ice samples to make their conclusions

    The scientists also used powerful computer climate modelling to confirm their results.

    ‘This is the first time anyone has clearly identified the specific onset of the cold times marking the start of the Little Ice Age,’ says lead author Gifford Miller of the University of Colorado at Boulder.

     

    ‘We also have provided an understandable climate feedback system that explains how this cold period could be sustained for a long period of time.'

    'If the climate system is hit again and again by cold conditions over a relatively short period -in this case, from volcanic eruptions - there appears to be a cumulative cooling effect.’

    A chromolithograph Chrismas card from 1865 showing the frozen Thames: Scientists now believe that the prolonged period of cooling was caused by four tropical volcanic eruptions

    ‘Our simulations showed that the volcanic eruptions may have had a profound cooling effect,’ says NCAR scientist Bette Otto-Bliesner

    ‘Our simulations showed that the volcanic eruptions may have had a profound cooling effect,’ says NCAR scientist Bette Otto-Bliesner, a co-author of the study.

    ‘The eruptions could have triggered a chain reaction, affecting sea ice and ocean currents in a way that lowered temperatures for centuries.’

    The study appears this week in Geophysical Research Letters.

    Scientific estimates regarding the onset of the Little Ice Age range from the 13th century to the 16th century.

    Although the cooling temperatures may have affected places as far away as South America and China, they were particularly evident in northern Europe.

    Advancing glaciers in mountain valleys destroyed towns, and paintings from the period depict people ice-skating on the River Thames in London and canals in the Netherlands, places that were ice-free before and after the Little Ice Age.

    ‘The dominant way scientists have defined the Little Ice Age is by the expansion of big valley glaciers in the Alps and in Norway,’ says Miller, a fellow at CU’s Institute of Arctic and Alpine Research.

    ‘But the time in which European glaciers advanced far enough to demolish villages would have been long after the onset of the cold period.’

    Miller and his colleagues radiocarbon-dated roughly 150 samples of dead plant material with roots intact, collected from beneath receding margins of ice caps on Baffin Island in the Canadian Arctic.

    They found a large cluster of ‘kill dates’ between 1275 and 1300 A.D., indicating the plants had been frozen and engulfed by ice during a relatively sudden event.

    The team saw a second spike in plant kill dates at about 1450 A.D., indicating the quick onset of a second major cooling event.

    Tthe researchers also analysed sediment cores from a glacial lake linked to the 367-square-mile Langjökull ice cap in the central highlands of Iceland that reaches nearly a mile high.

    The annual layers in the cores -- which can be reliably dated by using deposits from known historic volcanic eruptions on Iceland going back more than 1,000 years -- suddenly became thicker in the late 13th century and again in the 15th century due to increased erosion caused by the expansion of the ice cap as the climate cooled.

    ‘That showed us the signal we got from Baffin Island was not just a local signal, it was a North Atlantic signal,’ Miller says.

    ‘This gave us a great deal more confidence that there was a major perturbation to the Northern Hemisphere climate near the end of the 13th century.’

    The team used the Community Climate System Model to simulate the effects of volcanic cooling on Arctic sea ice extent and mass. T

    The model, which simulated various sea ice conditions from about 1150 to 1700 A.D., showed several large, closely spaced eruptions could have cooled the Northern Hemisphere enough to trigger the expansion of Arctic sea ice.

    The model showed that sustained cooling from volcanoes would have sent some of the expanding Arctic sea ice down along the eastern coast of Greenland until it eventually melted in the North Atlantic.

    Since sea ice contains almost no salt, when it melted the surface water became less dense, preventing it from mixing with deeper North Atlantic water.

    This weakened heat going back to the Arctic and created a self-sustaining cycle that sustained the sea ice long after the effects of the volcanic aerosols subsided, according to the simulations.

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    Posted
  • Location: Marion County Oregon
  • Location: Marion County Oregon

    Don't forget all those cow farts.    We need cow butt mufflers big time!  Warm is cold and cold is warm. Only in today's world. 

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    Posted
  • Location: Manchester Deansgate.
  • Weather Preferences: Heavy disruptive snowfall.
  • Location: Manchester Deansgate.

    wonder if the Icelandic eruption caused Dec 2010?

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    Posted
  • Location: Beccles, Suffolk.
  • Weather Preferences: Thunder, snow, heat, sunshine...
  • Location: Beccles, Suffolk.

    Nyet! I think it was the fact that it came after 2009! I'll get my coat!

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    Posted
  • Location: Douglas Isle of Man
  • Weather Preferences: Warm summer days with calm seas to swim in, cold frosty snowy winters
  • Location: Douglas Isle of Man

    Interesting articles... what's the source? Are there any hyperlinks you can share to the full science behind these hypothesis? 

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